suspension bump travel

INTRODUCTION TO SUSPENSION

Why do cars have suspension?

The object of a suspension system is to isolate the body and its occupants from the irregularities of the road surface. Ideally the body should ride level and without vertical motion’ however bumpy the road surface. Another important feature of suspension is that it should keep the tires on the ground all the time. If there were no suspension the tires would tend to lift off the ground every time they passed over a bump at the same time, the shock as the wheels left the ground’ and then came down again, would be transmitted directly to the passengers.

What does a suspension?

Ideally the suspension should allow the wheels to move up and down so that they follow the undulations in the road’ while the body rides level. The first requirement therefore is that the wheels should be able to move vertically relative to the body. Every suspension has this wheel travel, which must be accommodated by some means.

How is the wheel movement accommodated?

Springs are normally used (Figure 1.1). As the tire strikes a bump in the road, so a vertical force is applied to the spring’ which is compressed or deflected. Therefore the wheel moves vertically relative to the body, and the tire maintains contact with the road surface. However, some of this force is transmitted through the spring to the body, which also tends to rise. If the springs are very ‘soft’ (i.e. have relatively low spring rates) the body rises little, but if the springs are very stiff the body rises quite a bit, depending on the severity of the bump. For a good ride, therefore, the springs should be soft.

Do soft springs have any disadvantages?

Although soft springs give a good ride in most circumstances, they allow the body to roll a lot during cornering. In practice, spring rates are a compromise between the requirements of ride and handling.

Why does a car roll?

When a car turns a corner, centrifugal force acts on the body and tends to push it outwards. However, this force is resisted by the tires, which grip the road; as a result, the body rolls about its suspension (Figure 1.2).

What is the disadvantage of roll?

When the car rolls excessively it is more difficult for the driver to control its direction. Also, when the car emerges from the corner and the body rolls back to the upright position, it will roll past the upright position if roll is excessive, and will take some time to right itself. Excessive roll can also make the wheels adopt unfavorable angles, depending on the type of suspension fitted.

Are any other components needed?

In its simplest form the suspension consists purely of the springs and their anchorages. However, when a spring is deflected it attempts to return to its normal position immediately, and if left to itself it goes past the normal position and then back again. It would take a number of these oscillations absorb the stored energy, and only then would the spring return to the normal position.

How is spring oscillation controlled?

Dampers are used to cut down these oscillations so that, after going past the normal position once, the spring soon returns to normal.

SPRINGING REQUIREMENTS

What are the basic requirements of a spring?

Ideally a spring should be arranged so that it is ‘soft’ enough to give a good ride; yet it should be able to absorb all the energy resulting from road shocks without using up all the wheel travel, and it should be stiff enough to prevent excessive roll on corners.

Are all these possible?

Suspension is a compromise between conflicting requirements, but it is possible to gain a good level of performance in all respects, although this can be expensive. First, however, it is necessary to appreciate how these parameters are measured, and how the important figures are calculated.

How is the ‘softness’ of a spring measured?

Every spring has a rate, which is an indication of how much the spring is deflected by load. This is normally indicated as load per unit deflection, given in Newton ’s per millimeter (or pounds-force per inch). However, when it comes to ride, the weight being carried has to be taken into account as well as the spring rate. For example, if a small mass is applied to a spring there is hardly any deflection, whereas a big mass applied to the same spring will give a big deflection, lithe mass is then bounced on the spring, the small mass moves very little, very quickly, whereas the big mass moves up and down quite a long way, but slowly. The amount the mass deflects the spring is called the static deflection, and the rate at which the mass bounces up and down is the natural frequency or periodicity of the spring-mass system.

How is the static deflection found?

The static deflection, D mm, is simply the mass carried divided by the spring rate, i.e. D = mass/spring rate.

How is the natural frequency found?

This is a bit more involved, in that the natural frequency = 30/ cycles/mm, where D is the static deflection, in meters.

What are typical values?

Values vary according to the type of car. For a small saloon the static deflection is often 110-140 mm, and the equivalent natural frequency between 90 and 80 cycles/mm. For a medium-size saloon, the figures might be 130-180 mm, between 85 and 70 cycles/mm; for a large saloon, 180-280 mm, between 70 and 55 cycles/mm. With some very advanced suspensions, figures of over 280 mm or under 55 cycles/mm are obtained.

Do these figures vary with load?

The actual figures for a car vary according to the load carried. When the car is in the kerb condition the frequencies will normally be higher than when it is fully laden, with four people and their luggage in the car. Also, there is normally little difference in the amount of weight carried by the front springs, laden or unladen, but a big difference at the back.

Typical figures for a medium-size saloon are

At the front the difference is small enough to be ignored, but at the rear it makes the ride firmer unladen than when fully laden. Ideally the frequency should remain constant, irrespective of loading, and at a satisfactorily low level.

Can a constant frequency be obtained?

A constant frequency can be obtained only if the spring rate increases in proportion as the load it carries increases. Of course the balance can also be improved by arranging for the increase in weight to be applied equally to the front and rear springs. In practice this is very difficult to arrange.

How is the stiffness of the spring measured in roll?

Basically, the stiffer the spring, the less the car will roll, although the spacing of the springs and the roll-centre height also affect the amount the car rolls. The roll stifThess, which is the measure of the way in which the springs resist roll, is given by:

Roll stiffness = C w x t x 0.08729 N m/deg

for independent suspensions, where C w is the spring rate at the wheel, known as the wheel rate, and t is the track of the car. For beam-axle suspensions:

Roll stiffness = Cs x s 2 x 0.08729 N m/deg

where C s is the spring rate, and s is the spring base, i.e. distance between the effective positions of the left- and right-hand springs.

In simple terms, this means that an increase in either the spring rate or the spring base (or track) will increase resistance to roll, and that more can be gained by increasing the spring base (or track) than by increasing the spring rate.

How can the spring base be increased?

With a beam axle, the spring base is the distance between the springs (Figure 3.1), and the practical width is determined by the necessity of giving clearance around the wheels and brakes.

In practice, this means that the spring base is about 70-80 percent of the track, and that the wheel rate in roll is only about 50-70 per cent of the wheel rate in bump. There is little that can be done to increase the spring base with beam axles.

Is independent suspension better, then?

A better balance between ride and roll stiffness can be obtained with independent suspension, because the wheel rate in bump is the same as it is in roll. So, assuming that the linkages are equally good and that the roll centre of the independent suspension is not very low (see later), independent suspension has this one definite advantage.

Can roll stiffness be increased in any other way?

The addition of an anti-roll bar increases roll stiffness and reduces roll. An anti-roll bar is a horizontal, transverse torsion bar, normally mounted in two rubber bushes on the body. The ends are turned round to form levers, and are attached to the suspension member or axle, either directly or through drop-links. When the front wheels strike an undulation in the road so that both springs are deflected, the anti-roll bar merely rotates, so it is not deflected and exerts no force on the body. However, when the car goes round a corner, and rolls, one lever goes upwards and the other downwards, so the anti-roll bar is twisted. The bar resists, and tries to twist the car body back to the vertical position. Generally, then, the .addition of an anti-roll bar reduces roll but does not affect the ride. The stiffness of an anti-roll bar is usually referred to as its spring rate in roll.

Does the anti-roll bar have any side effects?

Quite often only one wheel hits a bump, and in this case the anti-roll bar does alter the spring rate. What happens is that the anti-roll bar twists as the wheel is raised but, since the other wheel does not move, the bar twists over its whole length (in roll, the bar is twisted from both ends, as it were, so its effective length is half the actual length). This situation, called single-wheel bump, has a higher bump rate than when both wheels move upwards together. For example, if the spring rate of the anti-roll bar is 7 N/mm and the wheel rate of the spring is 20 N/mm, then on single- wheel bump the rate is 20 + 7/2 = 23.5 N/mm. If the proportions are of this order, the passenger will hardly notice the difference. However, if the spring rate is very low and the anti- roll bar is very stiff, a single-wheel bump will tend to rock the car, inducing what is called a roll-rock condition, which can be uncomfortable.

Can the resistance to roll be altered in any other way?

Although the roll stiffness depends purely on the spring rate in roll, the anti-roll bar and the spring base, the resistance to roll also depends on the roll centre. But in essence the higher the roll centre, the less the vehicle rolls. Why does a high rod centre reduce roll?

When a vehicle corners, the centrifugal force acts through the centre of gravity, and it is this that makes the vehicle roll. However, if we consider the front of the car (i.e. the front wheels, and the amount of the car they carry), then the body or portion of the body must roll about some point, and that is the roll centre (Figure 3.2). The force making the vehicle roll is called the tilting moment, which is the tilting force times its effective height. The effective height is the distance, h, from the centre of gravity of the vehicle to the roll centre. Therefore, to reduce roll, h should be kept to the minimum. If the two were at the same height, the car would not roll at all. It is for this reason that the centre of gravity of a racing car is as low as possible.

Apart from the problems with roll, are there any other limitations on how soft the springing can be?

Even if roll could be kept to the minimum by the use of unusual suspension geometry and anti-roll bars, there are limitations on how soft the springing can be. The main limitation is the need to absorb all the energy applied to the spring by road shocks without the spring ‘crashing through’. For example, let us assume that a spring has 76 mm of movement from the normal laden condition to full bump, and that the spring rate is 18 N/mm. Therefore, to compress the spring fully (or make it crash through), 1350 N must be applied by a bump in the road; the force will depend on the severity of the bump and the speed of the car, but loads of 890-1100 N can be applied quite often. Now, consider a car with a same amount of wheel travel, and a very soft suspension, with spring rates of only 10 N/mm. A force of 760 N would take up all the wheel travel (10 N/mm x 76 mm = 760 N; so if a force of 890 N were applied, not only would the springs be fully compressed, but a force 130 N would be applied to the body. That would jolt the car, and also create quite a noise.

Why cannot the wheel travel be increased?

More wheel travel can be incorporated to alleviate this problem, but there are a number of problems. First, the wheel arches have to be made taller to allow clearance for the wheels, and this can reduce passenger or luggage space. Secondly, the springs and dampers have to be longer, and there may be little room for them (especially in low cars). Thirdly, it is difficult to arrange for the suspension to give suitable wheel control for large suspension travel.

How much wheel travel can be provided?

It is normal for there to be about 75-100 mm from normal laden to full bump; up to

150 mm is practical, especially on big cars.

How else can ‘crash-through ‘be avoided?

The use of springs with progressive rates and self-leveling systems can allow the use of softer springs without the need for a lot of wheel travel. A spring with a progressive rate is one in which the rate increases as the spring is deflected. In the normal laden condition the rate might be 14 N/mm, after 25 mm of extra compression it might be 18 N/mm, and at fill bump after 75 mm of compression it might be 25 N/mm. Thus, although the rate at the normal laden condition might be lower than in our original example, the load needed to compress the spring fully would be slightly higher.

What does a leveling system do?

A leveling system allows a car to ride at the same height irrespective of its loading. Usually it is hydraulic, and as the load increases (as people get in, or as luggage is put in the boot) and the rear of the car goes down, so the hydraulic system pumps the hydraulic struts up, raising the rear of the car to the original height. Equally, when someone gets out and the car rises a little on its suspension, the system removes fluid so that the car falls to its correct level.

What is the advantage of self-leveling?

The suspension has to be designed to suit the car when the driver is alone, when there are two, three or four people in it, and when there is some luggage in the boot as well. With a normal suspension, every time someone gets in, the springs are compressed a little. So when the driver is alone, there might be 1 15 mm bump travel, gradually reducing to about 75 mm when the car is laden normally, and perhaps only 50 mm when fully laden. There must also be some rebound travel to allow the wheel to fall down below the normal position, for instance when the wheel goes over a pothole. Therefore, there might be 150 mm wheel travel (normally 75 mm bump and 75 mm rebound) but filly laden, when the bump travel is most needed, there would be only 0 mm travel. Now, with self-leveling there might still be 150 mm of wheel travel, but there would always be 88 mm bump travel and 62 mm rebound travel, for example. Not only does the car look better, because it always rides level, but there is effectively more suspension travel available, so softer springs can be used.

Is the amount of rebound travel important?

It is essential that the suspension has sufficient rebound travel, too little being a common fault with many earlier cars. In the first place, if the wheel is able to fall sufficiently to keep in contact with the road when it encounters a depression in the road surface, the ride is much more comfortable and there are less shock loads than if the wheel is hanging in mid-air for part of the time. But rebound travel is extremely important on cornering: when a car corners the body rolls, so as far as the suspension is concerned it is as if the inner wheel goes on rebound, and the outer wheel on bump. If there is insufficient rebound travel, the inside wheel will become airborne at reasonably high cornering speeds, thus reducing the cornering power. To keep some load on the inner wheel when cornering, at least 62 mm of rebound travel is needed.

What is the ideal suspension?

An ideal suspension would have very low frequencies in order to give a good ride, but would have the aid of progressive-rate springs so that the frequency remained constant irrespective of load. There would also be self-leveling, and the linkage would be designed to give high roll centers so that there would be little roll and anti-roll bars would not be needed. To go further, the suspension would need to be designed so that every bump or ripple in the road was detected before it was reached; a signal would then make the wheel move to allow for the bump, so that the tire maintained contact with the road surface at all times, with the car riding level.

Why are dampers needed?

Whenever the tire passes over a bump of any magnitude the springs are deflected. The amount of deflection depends on the size of the bump, and the speed and weight of the car. When the spring stops deflecting, it has a store of force equivalent to the spring rate and the deflection: with an 18 N/mm spring, and a deflection of 25 mm, the energy is 18 x 25 = 450 N. This energy than pushes the wheel downwards, and if there were no damping the car would continue to oscillate up and down on its springs for a long time. To prevent this continuous oscillation, dampers are fitted.

How does the damper cut out these oscillations?

The damper offers a resistance to any motion of the suspension. Therefore when the spring is deflected both the damper and the spring resist deflection; on rebound the damper again resists deflection, but this time it opposes the force exerted by the spring.

Should the damper exert the same force on bump and rebound?

Since the damper opposes the spring action only on rebound, the force it exerts should be greater then than on bump. In any case, if the damper exerts a large force on bump it just makes the ride harsher. Ideally, therefore, the damping force should be small on bump and large on rebound.

Should the damping force vary with speed?

On bump, the speed at which the suspension is deflected depends on the conditions, and can vary quite a lot. Therefore the resistance should increase as the speed increases. The rate at which the suspension extends on rebound remains constant, and depends on the natural frequency of the suspension, so the damping should exert a constant force. This will be achieved if the damping force is proportional to speed.

What would be ideal damping?

On a car, damping is a compromise between ride and handling. For a comfortable ride, damping should be very light on bump; on rebound it should be light enough to allow the car to traverse small bumps without any harshness, but stiff enough to control the amount of oscillations after each bump so that the car does not wallow. For handling, the car should have the minimum number of oscillations, so that the car does not float. However, if the dampers are very stiff they will apply very high initial forces when a car is turned into a corner, and this can also upset the cornering.

What form do dampers take?

On the earliest cars there were no dampers, and interleaf friction and friction at the suspension anchorages provided the only form of damping. However, since the springs were very stiff, and hardly deflected at all, the absence of damping was not too obvious. Later, when some attempts were made to make suspension softer, it was found that damping was needed, and friction dampers were introduced. These took the form of a number of friction discs clamped together and connected by levers to the suspension so that, as the wheels moved up and down, the friction faces rubbed against one another. These were not very consistent in operation, and gave identical damping on bump and rebound-which is not ideal, of course. The energy was converted into heat as the discs rubbed together; even in hydraulic dampers the energy is dissipated in the form of heat.

How does a hydraulic damper work?

The basic principle is that a piston moves up and down with the suspension, and as it does so forces fluid through a hole or a number of small holes. Because the holes have a small area, there is a substantial resistance to the movement of the piston. Obviously, the basic ‘hardness’ of the dampers depends on the area of the holes.

ANTI- ROLL BARS

Are anti-roll bars fitted to many cars?

A large number of modern saloon, estate and sports cars are fitted with anti-roll bars, both to reduce roll and to give the desired road holding characteristics. On racing cars, different diameter anti-roll bars are used for different circuits, and the links are arranged so that the length of the effective lever can be altered.

How does an anti-roll bar alter the handling characteristics?

The anti-roll bar reduces roll by increasing the spring rate in roll only-the roll rate or roll stiffness. Therefore, if an anti-roll bar is added to a suspension at one end only it alters the front-rear roll stiffness ratio, and this alters the handling characteristics. As a general rule, if an anti-roll bar is added only to the front suspension the car will under steer more, and if one is added only to the back the car will over steer more.

What characteristics are best, and where does the anti-roll bar come in?

For normal use, it is desirable that a car should under steer (but not excessively), since this is a much more stable condition, especially near the straight-ahead position. The trend in the 1960s was to use anti-roll bars only at the front to obtain the desired under steer, but more recently the trend has been to fit anti-roll bars at front and rear, although with a much stiffer bar at the front. Under steer is still the aim, but with less roll and less under steer than on some of the cars of the late 1950s and early 1960s.

What is the roll centre?

The roll centre is the point about which the car rolls when it corners. There is a roll centre at the front and one at the rear, and a line joining the two points is the roll axis- the axis about which the car rolls.

What fixes the height of the roll centre?

With a beam axle it is the links providing lateral location that determine the height of the roll centre. Thus with leaf springs, the roll centre is at the height of the spring anchorages; with a Panhard rod, at the point where the rod is connected to the axle; with the Watts linkage, at the fixing of the link to the axle. See Figure 9.5.

How much can these heights be varied?

The roll-centre height with a Panhard rod can be altered quite a lot, depending on how much room there is under the body. The Watts linkage gives a roll centre within a few inches of the height of the axle, since it cannot be installed very low or very high. With the conventional four-link arrangement the roll centre is above the axle height, although it is possible to fit the splayed links or the A-bracket below the axle, in which case the roll centre can be quite low.

How high should the roll centre be?

The height of the roll centre is dictated by the characteristics required, the distance between the springs on the axle-the spring base-and the characteristics of the front suspension. In most cases, though, the roll centre needs to be fairly high.

What difference does the height of the roll centre make?

The higher the roll centre, the less the car rolls; if the roll centre is above the centre of gravity of the car, the car will roll inwards on corners! Very high roll centers can give some undesirable characteristics but, since the effective spring base at the rear is almost always quite a lot less than at the front, a higher roll centre at the rear is needed to give good handling characteristics.

Are there any other important points about roll-centre heights?

When the car rolls, or goes down on the springs, it is important that the height of the roll centre should not vary too much. Apart from the four-link suspension, the roll centers of all these suspensions remain substantially constant when the car rolls or pitches. The variation in height with the four-link system is not normally sufficient to create problems, however.

What is roll steering?

Roll steering occurs when the vehicle rolls; as a result of the roll, the wheels are moved so that they are not parallel with the body longitudinally. Semi-trailing links, some combinations of double-link suspension with radius rods, and some linkages for beam axles give roll steering.

Let us consider a beam axle, located by a pair of radius rods, parallel to the car, but inclined upwards from the axle to the body. Now, when the car goes over a bump, and the axle moves upwards relative to the body, the radius rods will move to the horizontal. This lengthens the wheelbase, which is not critical in itself. However, when the vehicle rolls, one wheel will go up and the other down relative to the body. As a result, on the side where the wheel has gone up the wheelbase will have been lengthened, while on the side where the wheel has gone down the wheelbase will have shortened slightly. Therefore the axle will have turned relative to the body, steering it- hence roll steering. In this case, if we are looking at a rear axle, the wheels will be steering outwards relative to the corner, giving roll oversteer. If the rods were inclined upwards in the normal condition, then roll undersreer would result. At the front, roll steering usually results from geometrical inaccuracies in the steering linkage, so that as the car rolls the steering arm is pulled inwards or pushed outwards by the tie-rod. If there is any roil steering in the linkage it should be roll under steer, since this is inherently safe, but roll steering should be avoided if possible.

APPENDIX: SUSPENSION FORMULAE

b is the width of the spring blade (m), L is the distance between the eyes of the spring when laden (m), t is the thickness of the blade (m), n is the number of blades, and E is the modulus of elasticity, which (modified to allow for internal friction) is 159 x 106 kN/m 2 .

For a torsion bar, the spring rate is given as the twisting moment per angular deflection. When a lever is added, this can be converted into a rate for the vertical deflection of the end of the lever.

Spring rate (torsion bar, for deflection at end of lever)

G is the modulus of rigidity, which is 78.5 x 106 kN/m 2 in this case, d is the diameter of the torsion bar (m), l is the effective length of the torsion bar (m), i.e. half the length of the bar for an anti-roll bar, and e is the length of the lever (m). Spring rate (coil spring)

G is the modulus of rigidity, which is 81.5 x 106 in this case, d is the wire diameter (m), n is the number of free coils, and D is the mean coil diameter (m).

To find the number of free coils it is necessary to subtract the number of dead coils from the total number of coils. The dead coils are those that provide the abutment and so cannot be deflected, usually 1.5 to 2 coils.

Roll stiffness (independent suspension)

= C w x t 2 x 0.8729 N/deg

C w is the spring rate at the wheel, i.e. wheel rate (N/mm), and t is the vehicle track (m).

Roll stiffness (beam axle)

= C s x s 2 x 0.8729 N/deg

C s is the actual spring rate (N/mm), and s is the spring track (m).

The wheel rate is not the same as the spring rare, and depends on the effective leverage, or the separation of the springs relative to the track. Thus if the distance from the centre-line of the car to the spring on a beam axle is a, and the distance from the centre-line of the car to the centre-line of the wheel (i.e. half the track) is b, as shown in (Figure A.l (a)), then:

Wheel rate C w = C s x (a 2 /b 2 )  N/mm

With independent suspension the formula is similar, except that b is the length of the suspension arm and a is the distance from its pivot to the axis of the spring (Figure A.l (b)). With double-wishbone suspension the formula is modified to take into account the effects of the other wishbone on the geometry. The formula becomes:

Wheel rate C w = (C s x a 2 x c 2 ) /(b 2 x d 2 )  N/mm

where a,b,c and d are as shown in Figure A.2.

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Suspension Travel and Motion Ratio: Explained

• Motorsport Tuning Guides

If you’re into motorsport or have a passion for cars, you’ve likely heard the term “suspension travel” before. But what does it actually mean, and how does it affect your car’s performance? In this article, we’ll delve into suspension travel and its relationship with motion ratio, which is crucial for a proper understanding of suspension setups.

Understanding Suspension Travel

Factors affecting suspension travel, suspension travel in different applications, compression vs. rebound travel, understanding motion ratio, the importance of wheel rate, q: what is suspension travel, q: how does suspension travel affect a car’s performance, q: what is motion ratio, q: what is wheel rate.

Simply put, suspension travel refers to how far a component of the suspension can move over the full extent of its movement range. In most cases, we’re interested in the vertical wheel travel, which is the distance that the wheel can travel from full droop to full compression. However, suspension travel can also refer to any other part of the suspension we might be interested in.

There are many factors that go into deciding how much suspension travel we need. Two of the most important and interrelated ones are the required stiffness of the suspension we’re working with and the roughness of the surface that the vehicle is running on. These factors will be discussed in detail later in the course.

The required suspension travel varies greatly depending on the application. For instance, a stadium truck running on rough terrain needs a large amount of vertical wheel travel to absorb the energy of a landing and reduce the forces involved. On the other hand, a high downforce single-seater running on a smooth surface requires less travel to keep things like camber, caster, and toe within suitable limits as the car negotiates the circuit.

Another important aspect of suspension travel is how much of the travel is available in compression versus rebound. A sensible starting point is to allow for approximately 2/3 of the available travel in compression and 1/3 in rebound. Having the majority of our suspension travel available on compression allows the suspension to absorb undulations in the road surface, while the rebound travel is there to keep the tires in contact with the road as the chassis heaves, rolls, and pitches.

Motion ratio is closely related to suspension travel and describes how much one component moves relative to the other when they’re linked together. We’re interested in the motion ratio between a number of different elements, but the most common is between the wheel and spring and damper assembly. In almost all cases, this ratio will not be 1:1, and the value of the motion ratio will generally vary as the suspension moves through its travel.

When comparing spring rates between different cars, it’s important to understand that the motion ratio between the wheel and the spring isn’t identical. We care about the effective spring rate at the wheel, which is generally referred to as the wheel rate. By using the motion ratio, we can calculate the wheel rate so we can make more relevant comparisons between cars with different suspension systems.

A: Suspension travel refers to how far a component of the suspension can move over the full extent of its movement range.

A: Suspension travel affects a car’s performance by absorbing energy, reducing forces, and keeping the tires in contact with the road.

A: Motion ratio describes how much one component moves relative to the other when they’re linked together.

A: Wheel rate is the effective spring rate at the wheel, which takes into account the motion ratio between the wheel and the spring.

In conclusion, suspension travel and motion ratio are crucial aspects of suspension design and tuning that can greatly affect a car’s performance. The required suspension travel varies depending on the application, and a proper understanding of motion ratio is necessary for comparing spring rates between different cars. By optimizing suspension travel and motion ratio, you can improve your car’s handling and performance on the road or track.

• Suspension Travel: What Is It and How Does It Affect Your Car’s Performance? – https://www.autosimple.com/suspension-travel-what-is-it-and-how-does-it-affect-your-cars-performance/
• The Importance of Motion Ratio in Suspension Design – https://www.nolimitmotorsport.com/blog/the-importance-of-motion-ratio-in-suspension-design/
• How to Calculate Wheel Rate: A Simple Guide for Racing Suspension – https://www.speedwaymotors.com/the-toolbox/how-to-calculate-wheel-rate/31488

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A Guide to Bump Stops for Off-road Suspensions

As you research the web looking for bump stops for your off-road vehicle , it might be helpful to take a look at bump stops in general before you decide which product is right for you.

This short guide describes in some detail what a bump stop is, what it does, and outlines for you the reasons for using off-road bump stops . Additionally, we’ll explain the different kinds of bump stops that are available on the market today, along with a few unbiased recommendations.

• What is a Bump Stop?
• What is the purpose of a Bump Stop?
• How do Bump Stops Work?
• How do You Install a Bump Stop?
• What Size Bump Stop Do I Need?
• What Bump Stops are Used Off-road?

Whether you call them bump stops , jounce bumpers or axle snubbers, it all means the same thing. We’re talking about a small-but-ever-important component that works together with your suspension and, in some cases, is part of the suspension on your car.

In the case of trucks and SUVs, most bump stops are mounted to the frame just above the lower control arm of an independent front suspension or somewhere between the frame and the axle tube on the rear. Bump stops can also be found inside the shock absorber or on the shock shaft.

Depending on the design, a bump stop could be made of various materials. Factory bump stops are usually made of rubber or microcellular foam. Many aftermarket bump-stop manufacturers choose polyurethane for its durability and its capability to be used for injection-molded products.

Some bump stops are designed for trucks that go off-road. Two of the best are Hydraulic bump stops and Timbren Active Off-Road Bumpstops . Hydraulic bump stops use fluid, typically lightweight shock oil, to absorb suspension energy. Active Off-Road Bumpstops are made of natural rubber, designed to absorb the harsh jounce when the suspension bottoms out.

What is the Purpose of a Bump Stop?

The main purpose of a bump stop is to serve as a cushion when the suspension finally bottoms out. That way, there’s always a bit of protection to prevent metal from hitting metal or, in some cases, prevent the frame from traveling too far. In either case, bump stops help avoid damage to the suspension or the chassis, as well as preserving the integrity of the shock absorbers.

Ride quality

The most common type of bump stop used on production vehicles is made from rubber. These are simple to employ and low in cost. A common aftermarket step-up from rubber stops is urethane. But neither style of bump stop offers great ride quality. A better alternative to factory bump stops is Timbren’s Active Off-Road Bumpstops which provide a soft, comfortable bounce when the vehicle bottoms out.

If you’re planning to leave the pavement and cut to the off-road trail, you’re quickly going to find that factory bump stops are woefully inadequate for the task. Not only is the ride quality poor, but the loss of vehicle control can be rather dangerous. The best way to regain control of your off-road vehicle requires the use of bump stops designed specifically for rough terrain .

A modern suspension system has hundreds of different parts working together. There are, however, seven main sections to every suspension system:

• Wheels/Tires
• Shock absorbers
• Rods/Linkages
• Joints/Bearings
• Steering System

One of the tiniest components of the entire suspension system is the bump stop. If you understand the purpose of a bump stop, then you know how they work. Factory bump stops limit the travel of the springs and protect the axle and frame to a certain extent by preventing the metal frame from smashing down on the metal axle (as in a straight-axle setup).

Various types of bump stops

There are basically three types of bump stops:

• Factory bump stops
• Shock-absorber bump stops
• Off-road bump stops

All 3 types minimize the damage caused when the suspension bottoms out.

Off-road bump stops take it one step further by helping to maintain better ride quality on rough terrain, as well as giving the driver more control over the vehicle. Nitrogen bump stops and Active Off-Road Bumpstops are both designed to absorb the constant stress of bottoming out by allowing a better cushion between frame and axle.

There’s no real trick to installing a bump stop if it’s the kind that replaces the one from the factory. Most OEM bump stops are bolted on to the frame, so the after-market replacement required will be similar to the original. Just remove the old and bolt on the new right in the same spot.

Active Off-Road Bumpstops fit several off-road vehicles on both front and rear. Most of them are bolt-on kits, i.e., they bolt on using the existing holes in the frame. If the factory bump stop is removed by prying it out of a cup, you replace it by simply pressing the Active Off-Road Bumpstop assembly up into the same cup.

Installing Hydraulic Bumpstops will require a much higher skill set than that of the average person along with special tools for cutting, welding, grinding and painting metal. Each kit includes metal brackets designed to make the installation a little easier.

So, how do you install a bump stop? The easiest way possible! Having said that, the particular set of bump stops that meet your needs may cost more than the average, not to mention the price.

Of the many types of bump stops on the market today, the only style that gives you any choice in size are the hydraulic kind (sometimes called air-bumps). Hydraulic bump stops usually come in 2.0”- and 2.5”-cylinder sizes, including 2" 3" and 4" stroke lengths, adjusted using internal spacers. The cylinder diameter is decided by the weight of the vehicle and how it is used. The stroke length is determined by your suspension travel and where the bump stops are mounted.

2.0 Bump Stops work best for solid axle vehicles 5,000 lbs. or under used for extreme off-roading like rock crawling. For vehicles with relatively low ride heights, we recommend 2” or 3" stroke bump stops if you are tight for space. For vehicles with ride heights above 6-7", we suggest the full 4" bump stops.

2.5 Bump Stops can absorb significantly more energy than the 2.0 size, so they are better suited for solid axle vehicles over 5,000 lbs. or in highly leveraged a-arm/trailing arm applications. Mud trucks and desert racers with large amounts of suspension travel should run 4" travel bump stops, while vehicles with a-arms or low ride heights should use 2" or 3" travel bump stops.

There are basically 3 types of off-road bump stops:

• Active Off-Road Bumpstops (Timbren)
• Wheeler Superbumps
• TeraFlex Speedbump bump stops
• Hydraulic bump stops (Bilstein or King)

If price is no object, hydraulic bump stops are the way to go. They’re filled with shock oil and nitrogen and are adjustable allowing you to fine-tune them to your particular needs. You’re going to need a custom shop that specializes in made-to-measure installation because these bump stops work best in conjunction with your existing shocks. Two of the most popular brands are Bilstein and King. Average price: $700.00 - $1,000.00 US (pair).

TeraFlex Speedbumps use the same principle of a factory bump stop but look and act much like a hydraulic bump stop. Installation requires some customization. Average price: $300.00 - $400.00 (pair).

Wheeler Superbumps resemble factory bump stops but are much taller and provide better ride quality. Average price: $150.00 (pair).

Active Off-Road Bumpstops (Timbren Industries) are made of natural rubber and come in many shapes and sizes. Depending on what you drive, there is a custom kit that will fit your off-road vehicle. If you can remove a bump stop, you can install Active Off-Road Bumpstops on your chariot. Average cost: $225.00 US (pair).

If you’ve taken the time to read through this guide, you now know what a bump stop is, and more specifically, the purpose of an off-road bump stop.

Be sure and visit our Active Off-Road Bumpstops information page to see if they’re the right alternative for you.

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• Setting up VPP
• Getting started
• Creating vehicles
• Configuring vehicles
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• Extending VPP
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• Vehicle Toolkit
• Vehicle Joint
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• Other blocks
• Creating add-on components
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• Creating custom blocks
• VehicleBehaviour reference
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• Miscelaneous topics explained
• How suspensions work
• Configuring realistic vehicles
• Vehicle rigging notes
• Source Code vs. SDK
• Vehicle Suspension
• VPWheelCollider
• VPAntiRollBar
• VPAdvancedDamper
• VPProgressiveSuspension
• VPDynamicSuspension

Vehicle Suspension #

Suspension in vehicles may be configured in several ways with several components.

VPWheelCollider #

The base suspension properties are specified in the VPWheelCollider component for each individual wheel.

See VPWheelCollider Suspension for details.

VPAntiRollBar #

Anti-roll bars (also "stabilizer bars" or "sway bars") connect the two wheels of the same axle allowing a limited degree of freedom between their suspensions. When one of the wheels is pushed upwards, the stabilizer bar transfers a portion of that compression force to the other wheel, so its suspension compress as well. This reduces the body lean in turns at that axle.

Several working modes are provided:

• Stiffness: configures the stiffness ratio of the bar.
• Spring rate: configures the spring rate of the bar. The spring is applied based on the difference of travel between both suspensions.
• Legacy: applies an anti-roll rate based on the difference of compression ratio between both suspensions.

Here's an example of the effect of the anti-roll bar in the front axle. It shifts the weight of the vehicle to the rear axle so it gains traction in corners. Without front anti-roll bar the rear inner wheel just lifts up:

VPAdvancedDamper #

Provides realistic damper properties: bump, rebound, fast/slow bump, fast/slow rebound. Using this component overrides the base Damper Rate value in the affected VPWheelColliders.

VPAdvancedDamper is applied before other suspension components that modify the suspension damper rates. For example, if both VPAdvancedDamper and VPProgressiveSuspension are applied to the same wheel, then both will produce the expected effect. First VPAdvancedDamper defines the damper rate, and then VPProgressiveSuspension may increase it based on the state of the suspension.

Terminology #

• Bump : Refers to an upward movement or compression of the suspension caused by hitting a bump or obstacle on the road or trail.
• Rebound : The opposite of compression. It refers to the extension or return of the suspension back to its original position after being compressed by a bump or impact.
• Fast Bump : Refers to the response of the suspension to quick or sudden bumps or impacts.
• Slow Bump : Refers to the response of the suspension to slower or more gradual bumps or impacts.
• Fast Rebound : Refers to the speed at which the suspension extends or returns to its original position after being compressed by a fast bump or impact. A faster rebound allows the suspension to recover quickly and maintain traction on rough terrain.
• Slow Rebound : Refers to the speed at which the suspension extends or returns to its original position after being compressed by a slow bump or impact. A slower rebound provides more stability and control, especially on smoother surfaces.

Properties #

Defines the parameters to use:

• Bump And Rebound Only : Same bump and rebound rates for all contact speeds.
• Slow and Fast Rates : Separate fast and slow rates for bump and rebound.

Given an initial damper rate, this utility populates the fast/slow bump and rebound values with pre-calculated coherent values:

• Bump = 2/3 * Initial
• Rebound = 3/2 * Initial
• Low Speed Bump = 2/3 * Initial
• High Speed Bump = 1/3 * Initial
• Low Speed Rebound = 3/2 * Initial
• High Speed Rebound = 3/4 * Initial

VPProgressiveSuspension #

Increases the spring rate, and optionally the damper rate, along all or part of the suspension travel. This may be used to implement leaf springs , or bump stops at the ending segment of the suspension travel.

Shape of the proportionality curve applied when applying spring and damper increments:

• 0.5 = linear
• < 0.5 = slow increment at the beginning, then fast increment near the end.
• > 0.5 = fast increment at the beginning, then slow increment towards the end.
• Base spring rate in the VPWheelCollider: 50000 N/m
• Min Compression: 0.5
• Max Spring Rate Offset: 10000 N/m
• Linearity Factor: 0.5 (linear)

The suspension spring rate remains at 50000 N/m between compression 0% (no compressed) and 50% (half of the suspension travel length). When the suspension continues compressing beyond 50% then the spring rate offset is applied proportionally:

• Compression 0%: spring rate = 50000
• Compression 25%: spring rate = 50000
• Compression 50%: spring rate = 50000
• Compression 75%: spring rate = 55000
• Compression 100%: spring rate = 60000

VPDynamicSuspension #

Automatically adjust the suspension of one or several axles based on the current load, so the suspension remains at a given compression value.

The base spring rates defined in the VPWheelColliders will be used to determine the proportion of load supported by each wheel in the affected axle(s). Then, this component overrides the spring rates with the values based on its configuration.

VPDynamicSuspension is applied before other suspension components that modify the suspension spring rates. For example, if both VPDynamicSuspension and VPAntiRollBar are applied to the same wheel, then both will produce the expected effect. First VPDynamicSuspension defines the spring rate, and then VPAntiRollBar may increase or reduce it based on the state of the suspension.

Interval in seconds to recalculate the spring rate when the vehicle is stopped.

For example, in real trucks this is typically done each second, so the suspension keeps adapting when the truck is being loaded or unloaded.

Interval in seconds to recalculate the spring rate when the vehicle is moving.

For example, in real trucks this is typically done each 60 seconds, so the suspension keeps adapting to minor changes in load and conditions (i.e. fuel conditions, weight shifting on slopes, etc).

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Bump Stops 101: What Every Off-Roader Needs to Know

Bump stops are an essential part of any off-roading setup. But what exactly are they and why are they important for your off-roading adventures?

What are Bump Stops?

Bump stops are basically your off-road shock absorbers’ best friends. They are these little rubber or polyurethane blocks or pads strategically placed in your suspension system to cushion the impact when your vehicle hits its maximum suspension travel. Think of them as the protective cushions that prevent your suspension from bottoming out and getting damaged when you’re taking on rugged terrain.

Where are They Found?

You’ll typically find bump stops mounted near your vehicle’s suspension components, such as directly on the frame or axle. They’re positioned to engage with other parts of your suspension system, like the control arms or leaf springs, to provide that extra cushioning and prevent any harsh impact or damage.

What’s Their Purpose?

When you’re out on the trails in your custom-built Jeep or truck , the suspension is working overtime to absorb all those shocks from bumps, rocks, and uneven terrain. However, sometimes your suspension might reach its limit, especially when you’re hitting big obstacles or taking on steep inclines and declines.

That’s where bump stops come into play. They act as a buffer, absorbing the impact and preventing your suspension from bottoming out. By limiting suspension travel, bump stops help maintain stability and control over your vehicle, ensuring a smoother and safer off-road ride.

Other Bump Stop FYIs

Choosing the right bump stops.

When it comes to bump stops, one size doesn’t fit all. Depending on your vehicle’s make, model, and suspension setup, you’ll need to choose the right bump stops to match your off-roading needs. Whether you’re into rock crawling, desert racing, or overlanding, there are bump stops out there designed to meet your specific requirements.

Regular Maintenance

Like any other part of your off-road rig, bump stops need some TLC too. Make sure to inspect them regularly for signs of wear and tear, and replace them if necessary. Keeping your bump stops in top condition ensures optimal performance and protection for your suspension system.

Adjustability

Some bump stops come with adjustable features, allowing you to fine-tune your suspension setup for different off-roading conditions. Whether you need more cushioning for those hardcore trails or a firmer ride for high-speed runs, adjustable bump stops give you the flexibility to tune your suspension just right.

Other than bump stops, there are plenty of other vehicle components you need to get checked out when gearing up for a trail ride. Bring your rig to the Dixie 4 Wheel Drive auto shop and we’ll give it the right service and maintenance to ensure it can take on whatever the terrain throws at it.

We’re also the guys to talk to if you’re looking to do some Jeep or truck modifications . Leave it to us to bring your dream custom ride to reality.

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What Are Bump Stops?

If you are an expert in cars, you must be familiar with all the definitions of lowering springs, shocks and struts, as well as leveling kits. Without a doubt, all of them contribute to a good suspension system, from top to bottom. However, bump stop, a crucial part of the system, is not that famous. In fact, not many drivers know about this vital car component, which is quite a surprise. So if you are also wondering what bump stops are, you have come to the right place. In this article, our car experts will answer all your questions. From the definition of bump stops to their functions, we will cover them all. In short, anything you need to know about this important yet overlooked suspension part will be right here. 

The Definition of Bump Stop

Bump stops are car parts that limit the suspension travel. This part is a progressive rate spring, which is created to have a soft contact, followed by an increase in stiffness to avoid hard contact. In order to slow down the speed, it will be the first to make contact before any other suspension parts make contact with objections that might damage them and your car.

The aim of this car part is to improve the quality of the ride, as well as save car parts. In the case of a crash or a shock, a bump stop will stop the suspension travel and prevent any further damage to the shock.

The Benefit of Bump Stop

Normally, if car owners slam down your automobiles to its limits, or hit the rocky trails hard, the suspension can be bottomed out. And believe it or not, this is an issue with various factors. And without a doubt, it is very uncomfortable for both you and your passengers. No one wants to ride in a car that keeps damaging your back and axles. Not to mention, this issue can also destroy your suspension system. For that reason, the bump stops are created. In other words, this car part is the final line of defense we all need to protect against this kind of issue. 

How Bump Stops Work

The aim of bump stops.

We all agree that lowering kits are really fun, until something is damaged or someone gets hurt. And that is why the bump stops are invented. This car part is created with the purpose of improving the ride, as well as to protect the suspension of the automobile. With bump stops, you can soften the blow. With polyurethane bump stops or high-quality pairs of rubber, the impact becomes much lighter. 

How Does it Work

Car designers made bump stops with various designs and placed them in various locations. Some of them like Axle Snubbers ( also known as Prothane Bump Stops) are placed between axle and frame, while others are in line with the piston rods of the shocks. With the first location, the bump stops will absorb the impact first, then comes the axle. This design aims to protect the axle before slamming into the frame. With the second location, the bump stop will absorb the impact damage, adding another level of sustainability when the shock reaches its limit. 

In short, the snubbers as well as bump stops help reduce the damage and protect all car parts before the suspension reaches the limit. 

Brand of Bump Stops

Now that you know how important it is to the car, it is time to pick the best one for you. And this is why we should come to the brand that you can trust.

Belltech Bump Stop

When it comes to bump stops brands, the first thing to pop in mind is Belltech. With suspension protection as well as the quality of riding, Belltech is the brand that disappoints no one. Let’s take the Belltech Bump Stop Kit as an example. It is the perfect kit due to a wide range of sizes, as well as the ability to match the lowered ride’s new amount of suspension travel. Another plus point of this brand is that they use high-quality polyurethane, which is very sustainable. 

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Last but not least, it features integrated threaded studs. This is made for an easy bolt-on installation.

Daystar Stinger Bump Stops

Daystar Stinger Bump Stops is the next brand we need to mention. Not only is it a famous brand but it also focuses on adaptation. The bump stops from this company can work with any off-road situation with a turnable design. Compared with conventional bump stops, they have the benefits in strength. With three styles of easily-swappable EVS foam inserts, customers have different choices. One is a firmer, harder suspension protection, while the other is softer and more progressive stop. Last but certainly not least, the mixture of these foam densities, is the last product of this brand. It can match all the needs of your particular terrain.    

In Conclusion

Bump stops are one of the most essential car components, so always spend time to check and purchase the best one for you. Through online research, you can easily find information on all the top and suitable brands as well as styles. Not to mention, users can see which stops are recommended for your ride’s new height.

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Hydraulic bump stops, or air-bumps as they are sometimes called, are a critical component of any performance suspension system. Not only do they help protect the vehicle and suspension components from hard bottom-outs, they play a critical role in end-stroke damping.

As you can see from the above cut-away, hydraulic bump stops are far more than a simple air-cylinder, they have a full piston with compression and rebound shims just like a performance shock absorber.

How Does a Hydraulic Bump Stop Work?

Hydraulic bump stops are filled with shock oil and nitrogen pressure. During the first stage of the bump stop stroke, the shaft and piston compress the nitrogen pressure which acts like a spring with an exponentially increasing spring rate. This allows the first 1/3 of the stroke to be relatively soft with the middle 1/3 being significantly stiffer. The last 1/3 of the stroke (depending on oil level) is the second stage where the shock piston is forced through the shock oil and that is where the majority of the energy is absorbed. Of course, once compressed, that energy wants to be released so rebound valving is used to help prevent hard unloading of the bump stop.

While some customers are deterred by the cost of hydraulic bump stops, especially when compared to cheap rubber bumps, you definitely do get what you pay for. King Hydraulic Bump Stops are priced a bit higher than most other brands but making a bump stop that withstands high forces repeatedly for the duration of a long desert race requires high quality materials machined to very tight tolerances.

Bump Stop Brands and Styles

Just about every performance off-road shock manufacturer makes their own hydraulic bump stop and, just like with their shocks, they all do things slightly different to try and set themselves apart.

King and ADS both build their bump stops like they build their shocks with full size pistons, compression and rebound shims, and high pressure seals. While we used their larger 2.5 size bumps stops for our displays, when compared in matching sizes to other brands, their components are still significantly beefier. Both King and ADS bump stops are top mounted and fit using precision machined mounting sleeves instead of traditional pinch-style cans.

Fox hydraulic bumps stops are extremely popular due to their affordability and while their components are smaller and designed for mass manufacturing like their shocks, we've had very good luck with them over the years and would highly recommend them to customers on a budget.

Bilstein bump stops are practically identical to those made by Fox other than a rebound spring put in place of the shaft spacer. The spring is designed to help dampen the unloading forces of the bump stop and prevent that annoying clicking sound cause by the bump stop fully extending.

SPC Performance (Light Racing) calls their hydraulic bump stop a Jounce Shock due to its unique design. Unlike a traditional piston style bump stop, the Jounce Shock dampens both compression and rebound movement by forcing oil though externally adjustable needle valves instead of valving shims. This design makes the Jounce shock extremely compact, allowing it to fit in spaces that a traditional bump stop could not. One downfall to the Jounce Shock is that the way that it is made makes it extremely difficult to open and service without damaging it.

What Size Bump Stop Do I Need?

Hydraulic bump stops are typically available in 2.0" and 2.5" body sizes with 2", 3", and 4" stroke lengths which can also be shortened with the use of internal spacers. Just like when measuring for performance shocks , the cylinder diameter is decided by the weight of the vehicle and how it is used and the stroke length is determined by your suspension travel and where your bump stops will be mounted.

2.0 Bump Stops work best for solid axle vehicles 5,000 lbs. or under used for rock crawling, trail running, and mild desert runs. For vehicles with low (4-5" up travel) ride heights, we recommend 3" stroke bump stops if you can fit them or 2" stroke bumps if you are tight for space. For vehicles with ride heights above 6-7", we suggest full 4" bump stops.

2.5 Bump Stops can absorb significantly more energy than the 2.0 size so they are better suited for solid axle vehicles over 5,000 lbs. or in highly leveraged a-arm/trailing arm applications. Mud trucks and desert racers with large amounts of suspension travel should run 4" travel bump stops, while vehicles with a-arms or low ride heights should use 2" or 3" travel bump stops.

King hydraulic bump stop dimension courtesy of Filthy Motorsports :

Tuning Hydraulic Bump Stops

Bump stops are tuned by adjusting their internal nitrogen pressure using a nitrogen fill kit which includes a pressure regulator , connection hose , and an air chuck . Getting them set up correctly is a trial and error process and we find it works best to start with a pressure that is too high (350-400 psi) and slowly work your way down. With the bump stop pressurized, roll the o-ring on the shaft all the way up before going out for your first test run. You will notice that as your bump stops cycle, they will push the o-rings down to show you how much they have moved. Ultimately, when you are driving 95% all out, you want the bump stops to cycle almost all the way leaving about 1/4" left as insurance for those times when you hit something harder than you had expected.

Assemble a nitrogen fill kit with these parts from Amazon. Put together your own Nitrogen Fill Kit with a pressure regulator , connection hose , and an air chuck or no-loss air chuck . The only other item needed is a nitrogen tank that is available at any local welding supply shop.

As an Amazon Associate, we earn a small commission on purchases which does not affect your pricing.

More Shock Guides:

Shock Rebuild Instructions - Detailed step-by-step instructions for rebuilding high-performance shocks. Shock Rebuilding Tools - A list of tools needed to service high-performance shocks and coilovers. Shock Valving Guide - A guide to high-performance shock valving and valving shim configurations. Shock Tuning Guide - A guide to how high-performance shocks are tuned and valved to work well. Shock Valving Shim Stack Examples - A list of common, basic valving shim stack configurations for high-performance shocks. Coilover Spring Rate Calculator - A calculator to help you determine a good starting point for coilover spring rates. 4-Link Suspension Guide - A quick overview of the most important elements of 4-link geometry. Shock Rebuild Parts - A link to Filthy Motorsports' shock parts page. How To Measure For Coilovers - Order the right size shocks and coilovers by following these detailed instructions. Coilover Install and Setup Guide - Proper coilover installation, setup, and fine tuning instructions. Coilover Spring Re-Calculation Guide - How to easily correct coilover spring rates to achieve your desired ride height. ORI STX Struts Guide - An introduction to ORI STX Struts, how they work and how to tune them. Hydraulic Bump Stop Guide - A detailed overview of hydraulic bump stops and jounce shocks for off-road use.-->

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Bump / Roll Steer – Suspension KPI

Bump steer is a measure of the suspension toe angle change with suspension vertical travel.  Bump steer, given in Deg/m, is a measure of the toe angle change in degrees versus suspension travel in metres.  Roll steer is calculated in the same way as bump steer except the wheel travel is generated by applying a roll angle to the vehicle body.

Positive bump steer gives a toe in tendency with suspension bump and negative bump steer gives a toe out tendency with suspension bump.  As suspension systems are typically tuned to have a level of understeer, front axles typically have negative bump steer (toe out, understeer tendency on the front axle) and rear axles typically have positive bump steer (toe in, understeer tendency on the rear axle).

A common perception among tuners is that all bump steer is bad and zero bump steer is the idea scenario.  In reality it is a key tuning lever to deliver a predictable handling balance on a vehicle.  All  production cars have a combination of suspension understeer from compliance steer and/or bump steer.  A suspension system with no understeer will feel very responsive, maybe even too responsive for non-professional drivers.  Having a level of understeer in a suspension system delivers more intuitive handling and also improves high speed stability (reduces vehicle nervousness at high speed).

Typically production cars have front bump steer in the -2 to -10 Deg/m range and rear bump steer between 0 and 4 Deg/m.  The linearity of the bump steer curve is also important to ensure linear vehicle response during cornering.  A typical front suspension bump steer curve is shown below from  RACE .  The on-centre bump steer is -2.5 Deg/m.  The curve also has excellent linearity for wheel travel between 50mm rebound and 50mm bump.

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Informational Guide

What Are Bump Stops?

We explain, what are bump stops used for, and show you how to install some on your vehicle.

What are bump stops and why should they matter? If you care about the quality of your ride, you will want to know about this suspension component, which is just as important as shocks and struts .

In this article, we will answer - what are bump stops used for, and show you how to install some on your vehicle.

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The bump stop limits suspension travel, and it prevents other components from making contact with damaging items.

When used with shocks, the bump stop prevents travel before bottoming out, preventing wear to the shock. The bump stop can also be placed on the frame located above the axle to keep the metal of the frame from hitting other metal components.

Think of the bump stop as a shock absorber or cushion. Some bump stops are made with rubber, while others use a urethane construction. Either one is air-infused to produce plenty of support.

Why Are Bump Stops Important? (Are They Needed?)

What are bump stops for? With the right bump stops in place, the ride quality is improved. There will be less bottoming out, which ensures that vital automotive parts don’t become damaged.

Additionally, if you spend a lot of time off-road, you will want to protect your car’s suspension. With the uneven and rough terrain, the bump stops add more security. That’s why many users aim to figure out - what are bump stops on a Jeep?

As a rock crawler, you want less jarring, which is precisely what a bump stop achieves. The bump stops also ensure you have better control over your vehicle, instead of letting the suspension bounce and sway dictate where you are driving.

Types of Bump Stops: Hydraulic Vs. Rubber Explained

Rubber & urethane bump stops.

The first bump stops were made from rubber but are still widely sold today. These are the most affordable option but are less durable than other materials.

Urethane bump stops are more durable and lighter. Plus, they are flexible even when temperatures are low and compress well.

Nitrogen Bump Stops

These are often referred to as hydraulic bump stops or air bumps. They look like smaller shock absorbers, but one end is left free-floating. You can find a variety of sizes and strokes.

These oil-filled bump stops are charged with nitrogen and come with an adjustable shim pack. This is the type you will find when searching - what are bump stops for Jeep JK models?

Signs Of A Faulty Bump Stops: When to Replace

Because the bump stops regularly suffer from high impacts and are exposed to many materials, they will deteriorate over time. At the first sign of wear, you want to replace the bump stop for safety reasons.

Most often, the bump stops produce noise and vibration when wearing out. This condition is caused by the metal components of your suspension bumping together. It might also lead to changes in the ride, such as suspension sag, body roll, and swaying trailers.

You can also inspect the bump stops regularly to look for signs of wear. You might consider adding a visual inspection to your regular tune-up .

People Also Ask (FAQs)

Do bump stops affect ride quality.

The bump stop acts as a guide for the spring. With a high-quality bump stop in place, you experience a smoother, more controlled ride.

Does cutting bump stops lower car?

While the bump stop doesn’t change your height because it doesn’t support any weight, cutting it will create a harsher ride.

Can you drive without bump stops?

For many people, the bump stops are never touched; they are simply for precautionary reasons. Unless you are driving off-road or you are a stunt-driver wannabe, you could drive without bump stops and probably never notice a difference.

How much does it cost to replace a bump stop?

Bump stop kits cost between $25 to $500, depending on your vehicle and the quality. If you perform the installation yourself, you won’t need to pay a mechanic.

Are bump stops universal?

You can find many universal bump stops that will work on a variety of vehicle types.

Are jounce bumpers and bump stoppers the same thing?

The jounce bumper is a form of bump stopper, except it comes with three-stage compression that simulates variable rate mechanical springs.

What are rear bump stops? These vital suspension parts improve the ride quality, especially when heading off-road or across uneven terrain. With our guide, you know when to replace the bump stops and how to install this valuable component.

Gear-obsessed editors choose every product we review. We may earn commission if you buy from a link. How we test gear.

Does the Specialized’s New Stumpjumper and Its Genie Shock Change Trail Bikes Forever?

The 15th generation of the iconic Stumpjumper mountain bike is the best trail bike you can buy today.

The Takeaway: The 15th generation of the Stumpjumper is Specialized at its very best. It is a superb, highly refined bike featuring unique ride-enhancing technology in the deceptively simple Genie shock. This bike does everything it is supposed to do and does it extremely well. The Stumpjumper is the new benchmark trail bike.

Features and Details

Models and prices, ride impressions, notes from the field, q&a with chance farro.

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Specialized’s Stumpjumper is iconic. As the first production mountain bike , the Stumpjumper started a revolution in cycling when it debuted in 1981. As mountain biking developed and progressed over the decades, the Stumpjumper changed along with it. Specialized reinvented the Stumpjumper many times with different materials, new wheel sizes, disc brakes, and front and rear suspension to meet mountain bikers’ riding wants and needs.

Today, we see the launch of the latest generation of Stumpjumper, featuring an interesting new shock technology called Genie. By Specialized’s count, this new bike is the fifteenth generation of the full-suspension Stumpjumper platform (hence, it is dubbed Stumpjumper 15). The new bike is the best and most capable Stumpjumper the Morgan Hill, California-based brand ever produced.

And the Stumpjumper 15 is, so far, the best trail bike you can purchase in 2024.

What is Genie?

It’s not immediately apparent, but something interesting is happening inside the new Stumpjumper’s shock. As Specialized states in the bike’s press kit, “Compared to other air shocks on the market, Genie allows for a lower spring rate earlier in the stroke, with a higher ramp later in the ending stroke.”

It attains this with a custom two-stage air spring developed in-house at Specialized. While Fox manufactures the shock, Specialized has patents pending on this system. This allows Specialized to potentially have the Genie spring built into any brand’s air shock.

Specialized isn’t the first to tinker with a multi-stage air spring. Trek’s DRCV (dual rate control valve) from more than a decade ago was a two-stage air spring built into some shocks and even a few forks. But the DRCV air spring volume was initially smaller before switching to a larger-volume air spring partway through the stroke: Genie is exactly the opposite.

For the first 70 percent of the shock’s travel, the Genie air spring consists of the volume inside the main air chamber plus the air sleeve volume surrounding the shock body. This air sleeve is also referred to as the XV (eXtra Volume) sleeve.

At 70 percent travel, a ring on the air piston blocks off the ports that allow the main air chamber to communicate with the sleeve’s air chamber, reducing air volume to only what remains in the eyelet.

And…that’s really it. The Genie’s air spring volume is extra-extra-large for this first 70 percent of travel but reduces to that of a standard air shock for the last 30-percent.

It’s hardly even more complex with just a few more parts than a standard air shock. But while it’s a somewhat basic idea executed rather simply, Specialized is making some very grand claims about Genie’s benefits.

The short version is Specialized claims Genie offers the best of both shock worlds: The sensitivity of a coil spring but with the ease of setup, progression, low weight, and air volume tuning options of an air spring. The long version is found in a 15-page white paper that lays out—in great detail—how Specialized says Genie is better-er than any other shock.

The white paper states that, compared to a standard air shock, the Genie’s benefits include:

• 11.3 percent less bottom-out event time. (Defined as “The sum of all time spent with the shock fully bottomed out while riding.”)
• 57 percent less traction loss time. (Defined as “The sum of all times the rear wheel is slipping with respect to the front.”)
• 27 percent less traction loss intensity. (Defined as “The difference in the front and rear wheel speed when a slip occurs.”)
• 10.5 percent less chassis pitching. (Defined as “The speed at which the front triangle is bucked back and forth.”)
• 11 percent less uncomfortable vibration exposure. (Defined as “The amount of vibrations reaching the rider, specifically focusing on the range of frequencies that have been proven uncomfortable for humans to experience.”)

Another benefit of the Genie’s two-stage air spring is that it provides riders with a second tuning tool not available with a standard air shock. Not only is the end-of-stroke progression adjustable with volume spacers like most air shocks, but riders can also independently tune the air sleeve volume, influencing the feel of the spring in the initial stages of travel.

This adjustment allows riders to make the suspension initially supple or poppy without influencing the progression at the end of the travel. Likewise, riders can make the end-of-stroke progression soft and linear or ramp aggressively without altering how the suspension feels at the beginning of its travel.

For more insight into the Genie shock, see my Q&A with Chance Farro, Specialized’s Suspension R&D Manager, below.

For this generation, Specialized not only made a new bike, but the brand also reoriented its trail bike lineup. The outgoing Stumpjumper line consisted of two bikes: the Stumpjumper with 130mm rear travel (with a single pivot/flex stay design) mated to a 140mm fork and the Stumpjumper Evo with 150mm rear travel (using a four-bar Horst Link design) and a 160mm fork.

The new Stumpjumper 15 has 145mm of rear travel via Specialized’s signature four-bar Horst Link system, mated to a 150mm fork. This model supplants the 130/140mm Stumpjumper and the 150/160mm SJ Evo.

“The goal was to take the best attributes of Stumpjumper (snappy and nimble) and Stumpjumper Evo (capable and adjustable) into one platform that catered to a wider range of riding styles and terrain,” said Todd Cannatelli, Specialized’s mountain program manager.

I asked Cannatelli how Specialized settled on the 145/150mm combo. He responded, “The rear travel number can be a bit deceiving [on Genie-equipped bikes] as we are using more travel than a standard shock for a given force in many instances. The total travel of the bike is 145mm, but that number is not an apples-to-apples comparison to a bike without Genie.” Cannatelli added, “We of course tested with different fork travels, but we ultimately felt the bike was the most balanced with the Genie shock and a 150mm fork.”

Despite featuring less travel front and rear, the SJ 15’s geometry changes little from the outgoing Stumpjumper Evo (more geo details below).

For riders who crave a lighter trail bike—like the old 130mm Stumpjumper—I suggest checking out the new Epic 8 Evo. For riders craving the more gravity-oriented vibe of the old Evo, Specialized offers one Evo-ish model—the SJ 15 with a 160mm fork and a burlier build (see the models and prices section below for more info).

Cannatelli said the new Stumpjumper 15 frame is about 15 grams lighter than the old Evo (so, it’s closer to the Evo than the weight of the outgoing 120mm Stumpy) while maintaining the same stiffness and strength properties as the Evo frame.

Unlike many Specialized models, the S-Works Stumpjumper 15 is not a wholly different frame. It gets the same FACT 11m carbon designation as the less-expensive models, but the S-Works model uses a carbon link that saves a handful of grams.

Specialized claims the complete, ready-to-build SJ 15 frame with Genie shock in size S4 weighs 3,007 grams (6.6 pounds), which is quite light for a trail bike frame. The carbon link on the S-Works frame saves about 60 grams (0.13 pounds).

My second-from-top Pro model in the S3 size weighed a hair over 30 pounds without pedals, which isn’t bad for a modern trail bike with an SRAM Transmission and Maven brakes .

One of the most obvious visual changes is the elimination of the “sidearm” of the old frames that bridged the top tube and seat tube. This results in a cleaner and more traditional-looking frame. The seat tube was also reshaped—it now has a more abrupt and lower kink that increases the length available for seat post insertion. This should allow many riders to use a longer-travel dropper post.

Specialized also graced the new SJ with its latest execution of SWAT in-frame storage. Like the new Epic 8, the Stumpjumper gets a flush-mount, more waterproof door with a finger-friendly release lever.

Most models and sizes run 29-inch wheels front and rear. For riders who want to run an MX setup (see exception below), Specialized sells an aftermarket link ($75) that corrects geometry and kinematics to match the bike with dual 29-inch wheels.

All sizes of the Ohlins Coil model come from the factory with a 27.5-inch rear wheel and conversion link installed. If you buy one of these MX bikes and want to swap to a larger rear wheel, Specialized also sells the 29er link for $75.

The wheel size story for the two smallest sizes—S1 and S2—is somewhat different. These sizes are “only compatible with a 27.5 [inch] rear wheel so we could optimize the rear center and geometry for shorter riders to maintain the ride quality we wanted,” said Cannatelli.

As for kinematics, Specialized made a few refinements compared to the outgoing Evo. Some of them relate to optimizing suspension performance around the Genie shock (see the Q&A section below for a bit more on this), but it also decreased anti-squat slightly compared to the old Evo.

Putting a bow on the details, the SJ 15 runs a 34.9mm seatpost, BSA bottom bracket, ISCG ’05 tabs, and a UDH (universal derailleur hanger). Also note that this frame is only compatible with electronic drivetrains: If you prefer to ride battery-free, you’ll likely need to wait until the inevitible aluminum frame Stumpy 15 appears.

The new SJ also gets protected by Specialized’s new “lifetime, no-questions-asked, bearing replacement policy.” So feel free to ride through all the streams and blast it with a pressure washer.

I won’t get much into the weeds with specific numbers because most of them are in the geometry tables (one for SJ15 with a 150mm fork and one for the Ohlins Coil model with a 160mm fork) I’ve pasted here. However, although it runs slightly less travel front and rear, the SJ 15’s geometry is almost identical to that of the outgoing SJ Evo.

All SJ 15 bikes and frames ship with an accessory drop-in upper headset cup. This alternate cup provides +/- 1.0 degrees head tube angle adjustment (the geometry table shows the bikes as shipped with the middle cup installed).

Meanwhile, flip chips in the chainstay links offer +/- seven millimeters of bottom bracket height adjustment and +/- 0.5 degrees head and seat angle adjustment (bikes ship in the high mode). All told the head angle ranges from 63 degrees (slack cup and low BB setting) to 65.5 degrees (steep cup and high BB setting).

The seat angle is size-specific, but the geometry chart for the bike with a 150mm fork listed above is incorrect. When I questioned why the S3 was steeper than both the S2 and S4, Cannatelli confirmed it was an error on Specialized’s part and sent over the correct effective seat angles, along with the saddle height those angles are taken from (Lower saddle heights result in a steeper effective angle, while taller yields a slacker effective angle).

The correct seat angles are:

S1 - 78 degrees at 645mm saddle height (center of bottom bracket to the top of saddle) S2 - 77°, 690mm S3 - 77°, 735mm S4 - 76.5°, 780mm S5 - 76.5°, 825mm S6 - 76.5°, 870mm

There are four chainstay lengths for the six frame sizes. The S1 gets 430mm stays, while the S2 runs 432mm. Sizes S3 and S4 share 435mm stays, while the S5 and S6 share 445mm stays.

Note that geometry is largely the same whether the bike runs a 27.5- or 29-inch rear wheel, so long as the frame is fitted with Specialized’s wheel-size specific upper suspension link.

The new Stumpjumper arrives in five complete variants priced from $5,500 to $12,000. Specialized also offers the Stumpjumper 15 as an S-Works frameset.

S-Works Stumpjumper 15 - $12,000 Stumpjumper 15 Pro - $9,000 Stumpjumper 15 Öhlins Coil - $8,500 Stumpjumper 15 Expert - $6,500 Stumpjumper 15 Comp- $5,500 S-Works Stumpjumper 15 Frameset - $3,500

While the outgoing Stumpjumper was offered in both carbon and aluminum frames, the new generation, at launch, only comes in carbon. However, there are strong hints that an aluminum frame might arrive later this year.

Specialized Stumpjumper 15 Models and Prices

Four of the five complete bikes run a 150mm Fox 36 fork (the smallest S1 size uses a 140mm fork) with the Fox Float Genie shock. All Genie shocks have a climb switch and three-position open mode damping adjustment. These models also feature 29-inch wheels front and rear, SRAM Maven brakes (200mm rotors front and rear for most sizes; the two smallest sizes run a 180mm rear), SRAM Eagle Transmission drivetrain (the least expensive Comp model gets the new, OE only, S1000 Transmission rear derailleur), rims with 30mm internal width, and a Specialized Butcher front tire with the sticky T9 compound mated to an Eliminator rear tire with faster rolling T7 compound.

The remaining variant is for riders who want something more gravity-oriented. The Stumpjumper 15 Ohlins Coil features an Ohlins TX 22 M coil shock with a 160mm Ohlins RXF38 M.2 29 fork. This model also has a 27.5-inch rear wheel wrapped with a heavier-duty Grid Gravity casing tire, TRP DH-R Evo brakes with 220mm front and 203mm rear rotor, plus a 35mm long Deity stem. This model is not offered in the S1 size; it is only in sizes S2 to S6.

I found Genie’s performance impressive. It is extremely—and remarkably—sensitive. And it is supple exactly when you want it, yet with superb support and plenty of bottom-out progression.

All the potential drawbacks I fretted about—Would it feel too soft? Would it wallow and feel like it sits in the middle of the travel? Would it feel like the suspension hits a wall when the sleeve volume gets cut off?—never materialized. Props to Specialized, Genie is sorted. And the resulting performance of the new Stumpjumper is superb.

But Genie’s performance isn’t in your face. Overall, the bike doesn’t feel radically different from a well-executed and properly set up suspension bike. But you will notice that the rear suspension has all the benefits of really plush suspension without the drawbacks.

While the Genie effect may be subtle, it feels like Specialized comes closer than any other brand in realizing the suspension feel and performance that we’ve chased since, well, since suspension bikes were invented. And that’s essentially the ride of a coil-over shock initially with the performance of an air shock in the later stages of the travel.

It’s not just that the Genie is only great at smoothing chunder and sucking up big bucks, either. It works great everywhere: More traction, more control, a more stable chassis, and a smoother ride. It simply works. And it’s not fiddly, complex, or heavy either.

Plus the Genie doesn’t require proprietary mounting bullshit or a weird frame design. It hardly looks different than any other shock. It’s hard for me to think of a technology I’ve found so impressive on the trail yet has so little extra baggage.

However, based on a quick spin around the parking lot, many riders' first impressions will be that the Genie shock is too squishy and linear. Therefore, riders will assume it to be wallowy and bottom easily on the trail. The danger is these riders may feel that the suspension is “too soft” and try to air it up or reduce air volumes to make it feel more like a traditional air shock.

But don’t—leave the stock volume spacers in place, set the shock at 30 percent sag (16.5mm on the shaft), and ride a favorite trail. You’ll be surprised at how supportive and bottom-out-resistant the “too soft” shock is on the trail.

Many of the claimed benefits of Genie are the same as those of Cane Creek’s Tigon hybrid coil/air shock (about $1,000 with spring and hardware). In Specialized’s favor, though, the Genie is realized in a much lighter, more tunable, and sleeker package. Plus, it is custom-tuned specifically for the Stumpjumper. But if you can fit a Tigon on your bike, you should experience at least some of the performance benefits of the Genie-equipped Stumpjumper 15.

Between the lower anti-squat and the softer spring of the Genie, I expected the Stumpjumper’s pedaling performance to go out the window, and I imagined using the shock’s climb switch often. But that wasn’t the case at all. I was quite impressed with how efficiently the new SJ pedaled and how little bob I experienced. Much like its performance over bumps, this bike is settled and quiet when pedaling.

However, it is not an especially fast climbing bike, and it doesn't feel particularly swift on flatter trails (I suspect at least some of this is due to the sticky rubber front tire). The Stumpjumper pedals along well enough, but it doesn't have the crisp acceleration of a Pivot Switchblade , for example.

While the Genie shock is the Stumpjumper 15’s biggest story, there is much more to this bike. To be clear, this is not a great bike because it has Genie; it is a great bike, and it has Genie.

The chassis is superb. It feels robust and well-tuned, stout but not overly stiff. The geometry works well for a wide range of trails. The geometry (and shock) have enough adjustment options to fine-tune the bike for many types of riding—even occasional visits to the bike park. (However, the SJ 15 would not be my first choice if I knew I would be riding in a bike park a lot.)

Notably, the Stumpjumper 15 is a better daily driver than the old (and very good) SJ Evo. The old Evo’s vibe is enduro-adjacent and needs a bit of speed and steepness to feel its best. The new SJ has almost the same capability on the most challenging trails but feels faster and more agile when riding less extreme terrain, which makes the new bike more entertaining to ride across a wider range of trails.

If you find the new Stumpjumper is not quite enough bike for your steep and challenging terrain, it can be easily optimized for rowdy trails with its geometry adjustments. Riders can use a 27.5-inch rear wheel and drop in a new air spring to bump fork travel to 160mm. But if that’s what you need for your daily driver, buy the SJ 15 Ohlins coil model—it’s basically an improved version of the old Evo.

And since the new Stumpjumper has no weird standards, this bike will be easy to live with for a long time. Even if the future reveals some huge flaw with the Genie shock (I don’t see that happening, but who knows?) it has standard dimensions and mounting eyelets. So, owners can easily source a different shock for this frame.

I’m annoyed at Specialized because the Stumpjumper 15 is so well executed that it’s giving me nothing to complain about. All I got is that the textured finish honestly looks like there was an error when the painter tried to apply the clear coat.

Is the new Stumpjumper 15 with Genie the best trail bike available today? I don’t think one needs to try hard to make that case. This bike is dialed. But there are many great trail bikes on the market from brands big and small. I could list a dozen or more other trail bikes I’d happily ride. However, if you forced me to pick a single bike today, I’d go with the new Stumpy.

Random observations and reports from my time testing the bike.

• The Pro model I tested features a textured finish that I’m unsure about. It looks like the painters messed up the clear coat or the frame is covered in dried drink mix. No joke: One of my riding buddies asked if a soda can exploded and sprayed the bike. When covered with a clear frame protector, it looks like hell, with bubbles everywhere.

• I’m, again, going to mention the super long saddle clamp bolts employed by Bike Yoke. It’s extra concerning in this case because Specialized’s saddles are quite low profile, and the top of the bolts sit mere millimeters under the saddle shell. I’d suggest everyone (carefully) find shorter bolts or chop the stock bolts. I love the function of the Revive dropper, but Bike Yoke needs to refine its saddle clamp.

• The headtube angle adjustment system consists of just a drop-in upper headset cup and requires no tools to change. It’s extremely easy to swap—easy enough to be done trailside if you’re so inclined.

• Swapping the air sleeve and eyelet volume spacers can be done with the shock installed in the bike. However, I found the air sleeve very difficult to slide off the first time I tried—I needed to remove the shock from the bike to get a good enough grip to dislodge it. However, I successfully removed the sleeve with the shock mounted in subsequent attempts. Accessing the eyelet volume spacer may require a strap wrench.

• The Roval Traverse wheelset on my Pro test bike is very good. I’ve had a pair in for long-term testing before I received this test bike, and they’ve been trouble-free. I like their blend of lateral stiffness and vertical compliance. They also appear to be very good at warding off flats: I’ve rimmed out multiple times on both wheelsets with no flats (so far).

• The Traverse rims on my Pro test bike are laced to Industry Nine’s 1/1 one hubs (lighter than i9’s top-of-the-line Hydra but with slower but still speedy four-degree engagement). A US-made machined i9 stem complements the hubs. Both are nice little premium touches.

• Specialized launched the Mimic saddle padding in 2018 as a product specifically designed for women’s anatomy. Specialized has since found that all riders, no matter their anatomy, find the padding comfy and specify Mimic saddles more broadly. The Stumpjumper 15 Pro model I tested has Specialized’s Bridge saddle with Mimic, and damn, is it comfortable.

• SRAM’s Maven brakes are heavy and ultra-powerful. Are they too much brake for this bike? I’m sure some riders will think so. But while the SJ would be marginally lighter with a less powerful brake, I loved having the easy-to-modulate power and consistency of the Maven.

Specialized’s Suspension R&D Manager

This interview was edited for clarity.

Matt Phillips : I'm going to start with: Briefly explain Genie.

Chance Ferro : I guess the brief answer is what actually the technology is: A dual stage air spring. On the positive side, we have one large volume that we then cut into two chambers, basically creating a secondary spring ramp.

Matt : What are the benefits to the rider?

Chance : It started with playing with really [air] large volume, and really, the benefits were basically taking progression out of the spring, flattening out the spring curve, getting more usable travel, and kind of exploring that side of things. But then, of course, running into bottoming issues and lack of support and all that that you have with less progressive bikes and springs.

And then that’s where the Genie technology comes in to allow us to have the big volume, but then also get the progression and spring ramp back that we needed.

Matt : And what is the benefit to that big volume?

Chance : So the big volume provides more suspension used per bump, giving us more traction, more better bump compliance. It's a softer spring in that earlier part of the stroke that just tracks better. [It] acts like a longer travel bike in those zones, just overall smoother ride.

Matt : Okay, so all air springs are progressive. So how is Genie different than a standard air spring?

Chance : The Genie air spring is basically both linear and progressive, I guess you could say. And it's broken into different portions of the travel. From that sag point to 70%, we’re very, very linear.

It is kind of flat [like] a coil spring. It's not very progressive. And that’s what the big volume gives us, and that's kind of where we're getting those benefits and traction and all that.

And then at about 70% of the stroke, we create uber progression. It's even more progressive than your typical air spring at that moment where we need it. It’s giving us a Jekyll and Hyde kind of air spring.

Matt : Why is this approach better than using damping or kinematics to achieve a similar end result?

Chance : We’re using kinematics as well to kind of, like, blend it. So it definitely plays in with the bike. The bike is less progressive as well.

It’s pretty easy to make a less progressive bike or shock. But what was hard to do is create that Jekyll and Hyde feel. So we could either have progression or no progression. We couldn't have both with kinematics. All the kinematics are kind of on a swooping trend. Like, you’re gonna either kind of have a progressive setup or a linear setup. We couldn’t have one that aggressively changes. So that’s where this technology allowed us to do that.

Matt : It seems like Cane Creek's Tigon shock is touting many of the same benefits as Genie. What are your thoughts on this shock and why not just specify it on the new Stumpy?

Chance : Yeah, I’d say the Tigon's actually a really close reference to what Genie is doing. The idea of this secondary spring ramp using air springs is a similar idea, for sure.

Obviously, the big difference just being they’re using a coil, we're using complete air. I’d say, for what we're doing, [the Tigon is] quite heavy. It’s even heavier than your standard coil shock. So especially for a Stumpjumper, you know, it’s really important for us to have a lightweight shock.

So that’s probably one of the biggest differences. There’s also tunability. We love air springs for that. And then I will say, when you go to a shorter travel shock, coils actually become kind of challenging for some reasons.

On a short travel bike, you end up actually running a pretty stiff coil spring. So on short travel bikes, you can almost have a coil shock that’s too progressive, if that makes sense. So the combination of, say, like, a coil shock [with a secondary air spring] could be overkill. So, with, with what we’re doing, we're able to kind of maintain that sag and then still flatten out that spring curve with the big volume and then get the ramp so it plays well with kind of short to mid travel bikes.

Matt : Is Genie compatible with different wheel travels. Would it work on a 130mm travel Epic Evo or a 170mm travel Enduro?

Chance : Oh, for sure. Yeah. We’re definitely looking at things on our end. We’re excited about the technology.

We developed it for Stumpjumper in this mid-travel range. And we’re exploring where else it can go. We see a lot of potential for lots of different wheel travels, for sure.

Matt : How many extra parts in a Genie compared to a standard Float shock?

Chance : So we’ve added one sleeve, and then beyond that, it’s a piston band that lives on the main piston. That and a couple seals.

It might not be more than five parts with O-rings included, and most of those parts are: they’re kind of a reuse. There's already a seal head there, and we just modified it and made it work for us. So it’s a pretty surprisingly simple shock in that way.

Matt : The Genie is not a reservoir shock. Should riders have any concerns about heat fade?

Chance : Yeah, that was something that we wanted to check off. It’s a conversation even in our office. And so we actually did a study on heat fade between a lot of different rezi [resevoir] shocks and this inline shock.

And we did find that the [Genie] shock gets about 10% hotter. But when we actually measure the effect of the fade, it was actually no difference. So, essentially, if the [Genie’s] max temp was 180 degrees, the other shocks were at 170. But on the dyno, they didn’t fade any different based on that ten-degree difference.

So we feel really confident this thing will hold up against big rezi shocks and all that.

Matt : Is the suspension setup procedure any different when you get your new Genie-equipped Stumpjumper versus one fitted with a standard Float shock?

Chance : No. If you didn’t know this was a unique shock, you’d set up exactly the same way. Set your sag about 30%, and it’ll work great.

Matt : All right, so the Genie offers ability to independently tune initial spring feel and then end of stroke progression. How should riders use these tools to help dial in their shock based on rider weight, experience, and terrain.

Chance : I think it’s really more the latter. The kind of terrain they’re riding and the experience they want.

I don’t see people needing to change too much: The spring scales really well. It’s actually one of the benefits of this shock. The secondary ramp, it scales in accordance to the spring rate that you put in there. So heavy riders and light riders will have the same ratio of mainspring to the secondary ramp, which is not the case with hydraulic bottom outs or bumpers and things like that, where that secondary spring is kind of, you know, always set. So that's one benefit in terms of how you'd set it up for your riding style and terrain.

That’s where it gets pretty fun. We have a lot of cool adjustments. We now have two chambers that we can dial in the volumes of. The [outer air chamber volume] bands will affect the middle part of the stroke, and then the eyelet independently affects the end of the stroke. So really depends on what you want.

If you want, like, say, the most plush feel, you’re at a bike park or something, or really rough trails, you can take all the volume spacers out of that outer sleeve, and it’ll just feel really, really plush. That's the really big volume.

But you can still be a really aggressive rider with that setting. You can even then put the larger [volume] spacer in the eyelet. We've even seen some of our most aggressive riders loving that setup.

You can put that [outer] sleeve completely full and get a more poppy, snappy feel. It really does change the perceivable travel bike has.

Matt : Sort of related: What rider weight range is the stock tune designed for.

Chance : I’d say it’s no different than pretty much all of our bikes. From like 125 to 300 pounds. And a lot of that really is like dialing in the rebound range, making sure that we have a rebound setting that works well. The spring will scale even beyond that.

Matt : Are there different tunes for different rider weights or different size bikes?

Chance : Nope, they all come with the same tune. In the past we have done some size specific tuning. It was always on the rebound side just to make sure we can fit that in. But we were able to get a really nice broad range rebound adjustment so we're able to kind of fit it all in.

Matt : Shock service and service intervals: Are these any different with the Genie versus a standard Float?

Chance : Nope, it’s 100% the same. The procedure is slightly different, but if you know how to do an air spring service, it’s going to be a shoe in.

And yeah, as far as like who can service it? The same people that can service a normal shock. If you do it at home, you can do that. Shops and Fox will service them as well.

Matt : Is Genie suited to a suspension fork?

Chance That’s a great question. That's something that we're looking at right now. So I’d say it probably is.

Matt : Okay, cool. Will you offer Genie as an upgrade to other Specialized models? Like previous generation Stumpjumpers?

Chance : Like I said, we are still looking at it for other models and things like that. As far as aftermarket stuff, there’s no plans currently, but I think maybe some of the product managers and things, they’re looking at that because they’ve got a lot of questions. If there’s a demand for it, there’s potential for sure.

Matt : And what about riders who might not have a Specialized bike? And like, hey, I’d really like Genie on my bike. Is that, is it too bad: Gotta buy Specialized?

Chance : That's the current setup. But I mean, I would love to see if someone wanted to pull this off and put on something else. I'd be flattered.

Matt : All right, so this is kind of my final question. It’s got a bit of a long preamble. Stay with me here.

I feel like, as an industry, we’re still trying to educate riders on how to set sag properly and how to dial in rebound.

I’ve ridden Genie and I think the effects are there, but they’re pretty nuanced and subtle. And I think it'll take a somewhat savvy rider who's attuned to the finer points of suspension to really feel those differences on the trail. And it’s not something you’ll feel on a parking lot test ride.

Do you at all worry that Genie’s performance differences and benefits might be lost on some riders?

Chance : I don't think so.

If you’re looking at the tuning aspect of it, I think that's something that we're not really pushing. The tunability. I think the tunability we look at kind of like the head angle adjust on Stumpjumpers and all that. It's there for the really discerning riders that want to get into that level. But we basically wanted the shock to be as good as it could be out of the box.

So, like, the way it comes is our preferred tune. It’s really the point of view of the bike, and we feel it just basically is a holistic, great ride as a whole bike. So I don’t think you really need to get into the nuances to appreciate it and just basically have the best Stumpjumper we can have.

A gear editor for his entire career, Matt’s journey to becoming a leading cycling tech journalist started in 1995, and he’s been at it ever since; likely riding more cycling equipment than anyone on the planet along the way. Previous to his time with Bicycling , Matt worked in bike shops as a service manager, mechanic, and sales person. Based in Durango, Colorado, he enjoys riding and testing any and all kinds of bikes, so you’re just as likely to see him on a road bike dressed in Lycra at a Tuesday night worlds ride as you are to find him dressed in a full face helmet and pads riding a bike park on an enduro bike. He doesn’t race often, but he’s game for anything; having entered road races, criteriums, trials competitions, dual slalom, downhill races, enduros, stage races, short track, time trials, and gran fondos. Next up on his to-do list: a multi day bikepacking trip, and an e-bike race. 

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California Bay Area Suspension Help

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Hi All... Not sure if this is the right forum for this post, but I'm looking for either someone with a garage willing to help me out, or a reputable/honest garage in the Bay Area (East Bay - Oakland, Walnut Creek, etc) to replace some front suspension components on my '83 240D. I'd do it myself, but I left most of my tools in Michigan. I was planning to do the replacements before I moved, but didn't have time. The car is in great condition, so I expect it will be a pretty straight-forward job. The rubber is all dried on most of the joints, so I want to replace it before failure. I have most (if not all) of the necessary components already, so if you're going to recommend a shop, it'd be helpful if you could tell me if they let you bring-your-own parts. While I'm at it, a good AC shop recommendation would be great. Thanks in advance! Craig  

This sounds like it would make a good Craigslist ad. Dkr.  

Hi Craig - If you need tools, harbor freight is on contra costa blvd in Pleasant Hill and you can get a decent set of whatever you need for as reasonable as it gets. Beats paying someone to do it. There is an indy Benz guy on Mt. Diablo off California Blvd in Walnut Creek, but I have no experience there and don't know how expensive it is.  

the guy in Lafayette is Jerry Figueroa, he works at Lafayette Motors, 3470 Golden Gate Way, Tel. (925) 284-4852 He quoted me a very reasonable price (about 1/2 of other shops in the area) to replace my ball joints, I still haven't found the money to do them yet but I visited him at him shop and he seems very knowledgeable. Call him about bringing your own parts, if they're not quality (i.e. Lemfoeder) then he'll probably be reluctant to use them. There are about four other shops in the area I can name for you if you need them.  

dave33333 said: the guy in Lafayette is Jerry Figueroa Click to expand...

Dieselkraut is left coast isn't he?  

Thanks Dave! I just called California Star in Lafayette... They want $1750 to swap the joints/control arms (using my parts). It seems steep to me, considering I am relatively confident I can do the work myself in a weekend if given the space. I'd be out $200 for the spring compressor, but I'd say it's money well spent and something I'd be happy to lend out to the community. I have lifetime alignment from Firestone, so I could probably save a bit there assuming it transfers across state borders. I'll give Lafayette Motors a call and see how it compares.  

autobahn187 said: ... They want $1750 to swap the joints/control arms (using my parts)... Click to expand...

Thanks! I'm waiting to hear back from Lafayette Motors. Seems like a nice crew over there, but we'll see how nice their price ends up.  

Jerry walked through the whole job with me today and pointed out some smaller nagging issues I've been putting off and offered to fix them up as part of the job... Engine mounts, fuel tank hose/strainer, caliper lines, etc. I already had the parts for most of it. His quote came in right where I had hoped. I'll follow up when all is said and done. Again, Jerry seems like a great guy. Super knowledgeable and friendly.  

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Pushrod Suspension Explained: How It Works, And What Makes It So Special

T he Lamborghini Aventador became the first mass-produced car to feature a racing-inspired pushrod suspension design when it debuted in 2011. A pushrod or pull-rod suspension is unlike the outboard suspension systems you'll find in a standard road car or SUV. The pushrod design incorporates a double wishbone setup with a few elements of a McPherson strut suspension. It is all part of an inboard suspension system popularized in F1 racing.

The late, great Colin Chapman and the Lotus F1 racing team have fiddled with inboard suspension and pushrod designs since the early 1960s. The inboard suspension design favors aerodynamics and conceals the dampers, springs, torsion bars, anti-roll bars, and other components behind or under the vehicle to improve airflow. In the 1970s, Gordon Murray and Brabham introduced the innovative pull-rod suspension design.

The pushrod and pull-rod systems feature struts across the chassis instead of vertically-oriented shocks and struts in a standard car. The difference between a pushrod and a pull-rod is the orientation and how the rod moves to counteract bumps on the road.

Read more: Cars That Will Blow You Away In 2023 And Beyond

How Does Pushrod Suspension Work?

The pushrod suspension in a typical F1 racing car consists of upper and lower wishbones and a suspension rod or torsion spring. The actual pushrod connects the torsion spring to the top of the wheel. A pushrod mounts from a higher point on the chassis to a lower part of the wheel assembly. When the tire goes over a bump, the upward force pushes the pushrod upwards and to the chassis.

But in a pull-rod, it's the other way around— the pull-rod mounts from a lower point on the chassis to a higher part of the wheel assembly. When the wheel encounters a bump, the wheel pulls on the torsion spring instead of pushing. Pushrods and pull-rods allow race car designers to relocate the suspension components closer and lower to the ground, enabling a lower center of gravity to enhance high-speed stability, cornering, and handling while reducing body roll.

Since the suspension components are "hidden" in a pushrod or pull-rod, there's less drag and better downforce. However, pushrods generally have a stiffer ride comfort on public roads and are expensive to produce. But on the racetrack, a pushrod suspension ensures more tire contact to maximize grip.

Read the original article on SlashGear .

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Hollywood, ca travel, photos information and news.

Hollywood has something that is more powerful in the minds of those who come to see the words written on hill that say "HOLLYWOOD". It has star power...everybody either wants to be a star or see one when they come to Hollywood.

What's so fascinating about fascinating Hollywood is the name itself has no intrinsic meaning other than what it has become. The founders of Hollywood, Harvey Henderson Wilcox and his wife, Daeida, established it as a residential development. Did Daeida select the name after she met a lady on a train whose summer home was called Hollywood, as some suggest? "The Father of Hollywood" by Gaelyn Whitley Keith attributes the founding to H J Whitley in 1886. Whitley Heights is on the National Registry and the Whitley, himself, is buried in the Hollywood Forever Cemetery.

Hollywood isn't a city at all, actually. At an election on November 14, 1903, the residents of Hollywood voted to incorporate as an independent city but did an about turn in 1910 when they sought a reliable water supply and felt that would only be assured by being annexed into Los Angeles. The region has really run with the name and trademarked it, emblazoned it on the hills and spread the word about this place throughout the world.

When you visit, you'll see thousands of tourists from around the globe coming to Hollywood, putting their footprints and handprints into the castings of the famous celebrities next to Mann's Chinese Theatre, buying souvenir things with HOLLYWOOD on them, and taking tours in buses that provide narratives of the famous people. The Grayline Tours actually stop in front of celebrity houses and wait for a sign of someone to come out or wave. It's pretty crazy, but that's how it goes in a star-crazed place.

When you visit Hollywood, there's a lot to see and do.

Capitol Records, 1750 N. Vine, at the historic intersection of Hollywood and Vine. Landmark building is one of Hollywood's icons and built like a stack of records.

Universal Studios Hollywood, (818) 508-9600. Located off the Hollywood Fwy. at the Universal Center Drive and Lankershim exits. Includes popular attractions based on movies, back lot tours of actual film studios, and City Walk, a free admission entertainment, shopping and dining attraction. Open daily, except Thanksgiving and Christmas. Operating hours vary.

Walk of Fame - honors more than 2,000 stars of motion pictures, television, recording, radio and theatre. The Walk is located on Hollywood Blvd. between La Brea and Gower and on Vine Street between Yucca and Sunset Blvd. Approximately 20 new stars are added each year.

Where to stay? Renaissance Hotel, which is connected to the Kodak Theater is very nice and has city lights views, or Hollywood hills with the Hollywood sign. Magic Castle Hotel is across the street, and Roosevelt Hotel Hollywood is just down the block. It has ghosts, some say, but you'll more often see famous celebrities making phantom appearances.

• HOLLYWOOD, a Name That Spells Magic
• Hollywood, Fame & Fascination Seen at Fort MacArthur in San Pedro

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