Chassis engineering herb adams pdf free download

Library of Congress Cataloging-in-Publication Data. Adams, Herb. Includes index. ISBN 1. Not everyone agrees on yerb the optimum values are, but Chapter 7 explains some of the considerations involved. The author discusses the geometry of an unequal length wishbone suspension, roll center movement and bump ste.

Three-Link-A three-link rear suspension uses only three links to locate the axle longitudinally in the car Figur e This means lbs. The length of the arms that feed the stabilizer.

This is called roll understeer, because it pdd the car turn less as the body rolls. The arrangement of the control arms in the side view determines the anti-dive characteristics of the front suspension.

One g is simply the force equal to gravity here on Earth? Adams Herb Chassis Engineering. Share Embed Donate. Main Chassis Engineering. ISBN Your tags:. Send-to-Kindle or Email Please login to your account first Need help? Please read our short guide how to send a book to Kindle. The file will be sent to your email address. It may take up to minutes before you receive it.

If some of the total Ibs. The total is not additive, but is a vec tor amount that can be used in combination as shown on the Circle. Every driver has experienced the effects on han dling of this condition. When exiting a turn, a car that has normal understeer will have oversteer at full throttle. The reason for this change in cornering attitude on the same car in the same corner can be explained by looking at the Circle of Traction. As the driver asks the rear tires to absorb more accelera..

Acceleration Effects-The extreme example of this condition is a car making a wheel-spinning start. If there is enough power to cause both rear wheels to break traction, all of the tires' traction is being used in the accelerating direction. As shown in the Circle of Traction diagram Figure , this condition results in zero cornering power available from the tires to restrain the car from side loadings.

The results of this lack of lateral force from the tires will cause the rear of the car to "fish-tail. A car 's lateral acceleration can be measured on a skid pad, which is a flat area of pavement usually to feet in diameter. The car is driven around the circle as fast as possible, the time is measured, and the lateral acceleration, expressed in g's, is calculated from the time and size of the circle.

Braking EffectsThe effects of braking are similar but opposite. We know that locking the front tires will make the front-end go straight regardless of the steering angle of the front wheels. When the front tires are locked up, all of their available traction is being used to absorb the braking forces , so there is none left to provide the cornering power needed to make the car turn. On a moving car, the distribution of acceleration, cornering and braking forces is constantly changing.

If the driver and the chassis tuner are aware of how these changes affect the balance of the car, they will better understand what is needed to tune the chas sis for maximum performance under all of these driving conditions.

One g is simply the force equal to gravity here on Earth. If an object is said to weigh pounds, the force of gravity on it equals pounds. If this object is subjected to a second force of 80 pounds, we would say it has an. This system of describing forces affecting common objects-like automobiles-is more conve nient than using pounds of force, since it eliminates the need to recognize the weight of the object.

For instance, a lb. The same lb. By describ ing cornering forces in g's, various cars can be com pared equally, regardless of their individual weights. It is measured on a skidpad and expressed in g's.

A skid pad is a flat area of pavement with a painted circle, usually to feet in diameter. The car is driven around the circle as fast as possible without spin ning out, the time is measured, and the lateral accel eration is calculated from the time and size of the circle.

A typical late-model stock Corvette can cor ner at. A road-rac ing sedan, however, does considerably better. Our Trans-Am race car produced 1. A simplified formula for determining a car's cor nering power on a skidpad is: 1. For example, if a car takes 12 seconds per lap on a foot radius skidpad, the computation is as follows: 1.

Now, let's take all of this information, and apply it to a discussion on weight distribution and dynamics. By using the tire performance curve Figure shown in Chapter 1, page 2, it is possible to determine how much traction is available at each individual tire. If you know how much vertical load there is, and how much traction is available, you can determine how much total cornering power the car has available.

Knowing the individual tire traction limits can also tell you some of the handling characteristics such as understeer and oversteer. If a car goes around a corner with the front of the car point ed toward the outside of the turn, it is said to under- Weight distribution is how much weight, or load, each tire has on it at rest.

However, when the car goes around a turn, weight will be transferred from the inside tires to the outside tires, which is known as lateral weight transfer. The more weight on a tire, the less trac tion it will have. With this knowledge, you can control the amount of weight transfer so your outside tires will have the maximum traction available. Understanding thi s relationship is a fundamental key to good handling.

Photo by Michael Lutty. If a car goes around a corner with the rear of the car sliding toward the outside of the turn, it is said to oversteer and it is loose. For an illustrated example, see Figure These weights change due to load transfer. The changes in loading are the result of forces acting on the car.

The following examples illustrate how some of these forces can change the individual vertical loads on each tire of a car.

Using this type of analysis is helpful in under standing how the static and dynamic weight distri bution of a car can affect its handling characteris tics. Understeer is the condition where a car needs more than normal front-wheel steering angl e to go around a corner; the front-end of the vehicle tends to break loose and slide, or push toward the outside of a tum.

Oversteer is when a car needs less than normal front wheel steering angle to go around a corner; the rear end of the vehicle tends to break loose and sl ide outward. But the important concept to understand is that the traction available from a tire is dependent on its vertical load. The confusing aspect is that the percentage of traction improvement goes down as the load goes up. As we look at the following exam ples, keep in mind that the traction available values in the charts were taken from our tire performance curve, Figure , page 2.

This theoretical car has Ibs. Using the tire performance curve in Figure l-Lon page 2, you can see that you would have Ibs. The total traction would be Ibs. See Chart Once you know the weight , you can take this information and compare it to the tire performance curve of your tires such the one shown in Figure I-I , p. Of course, once the car is moving, these weights change continually and affect the traction available, so you need to understand the forces that control these changes. Photos by Mi chael LUfO'.

Example Two As soon as a car starts to go around a corner, its vertical tire loadings will change. Because of the cornering force, weight will be transferred from the inside tires to the outside tires Figure See Figure When a car goes around a corner, some of its weight Figure The amount of lateral weight transfer is dependent on transfers from the inside tires to the outside tires.

This causes the the weight of the car, the magnitude of the cornering force, the weight on the outside tires to increase while the weight on the height of the center of gravity H , and the track width T.

On a car with equal front-to-rear weight dis tribution, this lateral weight transfer would be split evenly to lbs. If the car turns left, the left-side tires will lose lbs. At these tire loadings, the traction available would be lbs.

To see where we got that total, look at Chart Again, the traction available was calculated by using the tire performance chart, Figure l-l on page 2, as it will be for all of the charts in the following examples. Example Three One way to help equalize the weight on the tires during cornering is to preload the inside tires. This is done by moving some of the weight from the right side of the car to the left side of the car.

This will obviously only work on a circle track, where the cars During Cornering Available only turn left. Load Transfer From Cornering: bs. Under these conditions, the tire loadings and trac tion values would be as shown in Chart With the same lb. The static weights, cornering weights and traction avail able would be as shown in Chart This total is misleading, because if you look at just the front-end weights and traction forces in Chart 2 4, you see that there is Ibs.

Weight is moved from the right side of the car to the left side of the car, so that when weight is transferred, the loading on the outsi de tires will be less. SeeExample Three. This analysis shows that the car in this example will not only corner slower than one with equal front-to-rear weight distribution, but it will also understeer in the corners.

If the front traction is not able to pull the front weight as well as the rear trac tion can pull the rear weight, the front-end won't stick as well as the rear-end. This causes the car to understeer in the corners and to wear the right front tire faster than normal. Even more important is to note that although the total traction will permit the car to corner at 1. This means that because of understeer, the car can only corner at.

This is considerably less than the 1. Example Five This example is a combination for Examples 2, 3 and 4. Our interest with this combination is to see if the use of left-side weight bias will improve the cor nering power of-a front-heavy car and if it will solve the understeer problem.

The static and cornering weights as compared to traction forces are listed in Chart Plugged into the formula. Also, if we look at the front- r r dist ribution of cornering forces separately. This value is still considerably lower than the 1. Example Six The parameters for this exercise are the same as Example Five, except the chassis is wedged by adding Ibs.

Using a chassis wedge is a common method used to cure understeer. Wedging is accomplished by preloading the left front or right rear spring. When Ibs. Load Transfer from Cornering: lbs. Taking this data and putting it into Chart reveals that there is lbs. Once again , take the data from Chart and work it A car that is front-heavy will have less traction available from the front tires to pull the front-end weight around the corner, while increas ing the amount available at the rear to pull the rear-end weight around the corner.

If the front traction is not abl e to pull the front-end weight as well as the rear traction pulls the rear-end weight , the front-end of the car won 't "stick " as well, and understeer as a result. See Example Four. Photo by Michael Lutfy. Using a chassis wedge is a common method used to cure understeer on ci rcle track cars.

Wedging is accomplish ed by preloading the left front or right rear spring. When lbs. Work the formula for the total cor nering force , then just for the front and rear, as in Example Five. The front traction is still weak, but wedging the chassis increased the car's front cornering force from the value shown in Example Five, 1. This is a significant improvement, but it is still far less than the total 1.

Each tire has its own perfor mance curve, so you can't use these numbers to set up your car. However, analysis of these numbers does demonstrate some important guidelines: 1. The best cornering power is available when front-to-rear weight distribution is equal, assuming the tire size is equal both at the front and rear.

Left-side weight bias increases cornering power for oval track cars. Cars that have front-end weight bias heav ier in front will tend to understeer while cornering.

Wedging the chassis can reduce understeer in the turns and produce faster cornering. In general, the best cornering power will result when all four tires are equally loaded during cornering. Chassis tricks like left-side weight bars and wedging will only work on cars that turn left, like circle track cars.

This is called body roll, and the amount that it rolls is called the roll angle. Various means are available to control the amount of roll angle and to minimize its negative effects on han dling. Resistance to body roll can be achieved at the front of the car, at the rear of the car, or at both the front and the rear.

By deciding how much of the roll resistance is on the front and on the rear, you can control the understeer and oversteer characteris tics of your car. Since a tire develops its maximum traction when it runs perpen dicular to the track, this positive camber angle If a car has a large roll angle, the tires will not be perpendicular to the ground, so they will not provide the maximum cornering power. Less roll angle results in less positive camber, so a car will corner faster if the roll angle is kept small.

Different suspension geometry factors such as roll center height, swing arm length, the height of the knuckle, the length of the control arms and the posi tions of the control arms all contribute to the amount of camber change that is realized for a given amount of roll angle.

All of these relationships will be discussed in future chapters. This means that if the car rolls at a 4-degree angle, the outside tire will decamber 3 degrees, so the out side tire will lose 1 degree of camber in relation to the track. When a car rolls due to the cornering force, the tires usually roll with the car and develop a positive camber angle to the ground. By doing this, you help to keep the outside always an available means of controlling the roll front tire perpendicular to the track, even if there is angle on a given car.

Roll Center Height-As can be seen in Figure , Using excessive static negative camber can lead to raising the suspension roll center will reduce the roll problems, however. For most street applications, angle. Since the roll center height is an integral ele the maximum is about 1. For competition, static negative camber settings of 2 or 3 degrees are often used.

Tire temperatures can be used to optimize the amount of negative camber for most applications see Chapter Solutions Because there are limits to the amount of negative camber that can be used, it is important to control the amount of roll angle. The roll angle can be con trolled to varying degrees with the following ele ments of chassis design and setup.

Center of Gravity Height-It is easy to see why a lower center of gravity will result in less roll angle. Most cars are already as low as is practical, so will discuss its effects in Chapter 7. Track Width-Because the lateral spring base is proportional to the track width, a wider track dimen sion will reduce the roll angle.

As was the case with center of gravity height however, most cars already have as wide a track as practical. This means that for any given car, we can not expect to cause much of a reduction in the roll angle by increasing the track dimension.

Cornering Force Amount-As can be seen from the GTO in the photo on page 13, more cornering force will result in more roll angle. If you want to go around corners as fast as possible, you will have ever-increasing cornering forces , and therefore ever increasing roll angles. A car 's roll angl e is dependent on the distance between the height of the center of gravity and the height of the front and rear roll centers. The greater this distance, the greater the roll angle for any given cornering force.

The left drawing shows how an anti-roll bar is twisted when the body rolls in a tum. This creates forces at the four points where the bar is attached to the vehicle.

The forces are shown in the right drawing. Forces A on the suspension increase weight transfer to the outside tire. Forces B on the frame resist body roll. The effect is a reduction of body roll and an increase in weight transfer at the end of the chassis which has the anti-roll bar. Because the total weight transfer due to centrifugal force is not changed, the opposite end of the chassis has reduced weight transfer. This same car on race tires might corner at 1. If it did, the roll angle would increase to 4 degrees.

This means that cars that corner faster will need more roll stiffness to control the roll angle. Roll Stiffness The best way to control camber changes caused by body roll is to limit the roll angle by changing the roll stiffness of the suspension. The two most com mon means of controlling the roll stiffness on any given car are via the springs and the stabilizer bars.

Spring Rates-Increasing the spring rates will reduce roll angle. Unfortunately, raising the spring rates can also change other aspects of the car's han dling. As an example. This would double the roll resistance. But increasing the spring rates this much would also upset the ride motions and cause the car to understeer. Springs are dis cussed in greater detail in Chapter 5. Stabilizer BarsThe best way to increase roll stiff ness is to increase the size or effectiveness of the stabilizer bars, which are sometimes called anti-roll bars.

If a car is to roll, one wheel will be up in com pression and one wheel will be in drooping down. Stabilizer bars limit the roll angle of a car by using their torsional stiffness to resist the movement of one wheel up and one wheel down. Connecting both wheels to each end of a stabilizer bar causes this motion to twist the bar Figure The stiffer the bar, the more resistance to body roll it can provide.

Since the forces that cause the car to roll are being absorbed by the stabilizer bar. The stiffness of a stabilizer bar increases very quick ly as its diameter is increased. The effecti veness of a stabilizer bar is dependent on the length of the swing-arm as well as its diameter. The longer the swing-arm length, the less force the bar can provide with the same amount of movement at its end.

For example, a stabilizer bar with a swing-arm length of 6 inches will produce twice the amount of roll stiffness as a bar with a inch swing-arm length. Ou-tnch diameter sta bilizer bar. But, the stiffness of the bar must be properly transmitted into the chassis to do any good. The length of the arms that feed the stabilizer bar loads into the chassis have a dramatic effect on how much roll stiffness a given bar can produce on the chassis.

The longer the bar, the less effective it will be. For example, 6. Any lost motion at these connections will result in a loss of bar effective ness. Mak e sure you use high-quality, rigid materials for the con structi on of links and brackets. Also, the total roll stiffness of a given stabilizer bar is dependent on the stiffness of the frame mounting, the stiffness of the arms, the stiffness of the drop links, and where the drop links connect to the lower control arms.

Since the forces resisting the roll of the car are fed to the out side tires, it is possible to decide whether the front outside tire or the rear outside tire will absorb most of these forces.

If a car has understeer, too much load is on the front outside tire. By increasing the effectiveness of the rear stabilizer bar, some of this load can be transferred during cornering to the out side rear tire.

Doing this will eliminate the under steer, because the front and rear outside tires will be more equally loaded. The following examples show how transferring some of the forces resisting body roll can be fed into the rear tires to eliminate understeer.

These examples are for a cir cle track car that only turns left. On cars that turn left and right, the sample principles apply, but in opposite directions.

Example One For the figures in Chart on p. Left-Side Weight Bias: lbs. Roll Stiffness Front Only : lbs. Now, using the information in Chart , plug it into the formula for total cornering force, which was covered in Chapter 2. This is what happens when you apply roll stiffness at the front only. Let's see what happens when you equalize the roll stiffness. Example Two For this example, the car specifications are the same as Example 1, except that instead of having lbs.

When comparing the two examples, note that the total available g-forces are increased when a rear stabilizer bar is used to control half of the roll angle. Balancing a car's stabilizer bars is as an important aspect of chassis tuning as balancing the springs and the static weights. Increasing the rear roll stiffness reduces understeer. As a larger rear stabilizer bar will reduce understeer because of its ability to increase the dynamic weight on the out side rear tire, it will also work on cars that turn in both directions.

Suspension pieces in general look strong and rigid, but these pieces must handle loads in the lbs. Under high performance driving conditions, the wheels bend, the knuckles bend, the control arms bend and the frame bends. The worst source of deflection on a production car is the sus pension bushings. Suspension bushings are decep tively simple devices. Insignificant as they may seem, they have a very important effect on your car's handling. Therefore, the construction and quality of your bushings deserves close attention.

In most modern production bushings, the material bonded between the sleeves is rubber. During the 's, factory chassis designers were Even high performance street cars, like this Pontiac Trans Am, are ubj ect to the ills of rubber bushing deflection.

Rubber suspension bushings are used on most produc tion cars today. They consist of an inner sleeve, outer sleeve, and some form of material almost always rubber in the case of pro duction cars separating the two. Rubber bushings are used pri marily for cost, better road noise isolation and they don 't require lubrication. The rubber bushings were 1 cheap er to build, 2 offered better isolation from the jolts of the road and 3 didn't require lubrication.

Also, because the durometer hardness of the rubber could be tailored for specific chassis characteris tics, the engineers gained a new design flexibility they didn 't have with steel bushings. If rubber bushings have all of these advantages, why are so many car enthusiasts replacing their bushings with ones made of other materials? Obviously, there must be driving situations in which the rubber bushings do not perform as well as throughout this chapter.

For most street driving, rubber bushings work very well. But under high performance driving conditions, the rubber deflects, allowing the inner sleeve to move toward the outer sleeve, which changes the location of the control arm. Under most driving conditions, rubber bushings are the best choice. However, high performance driving demands less deflection, which a rubber bushing is not capable of providing. The excessive deflection of rubber bushings can have several adverse effects on high performance handling Figure Loss of Camber Control A tire generates its maximum cornering power when it is perpendicular to the road surface.

If the suspension bushings deflect when they are loaded by high cornering forces, the tire is forced to posi tive camber-and cornering forces are reduced Figure This explains why setting static nega tive camber helps cornering power.

By aligning the suspension with negative camber when the car is at rest, you anticipate the positive camber caused by rubber bushing deflection during cornering. If the suspension bushing material resists deflection, there is less loss of camber control. The loss of cornering power due to rubber bush ing deflection is a problem on cars with independent front suspension and on cars with independent rear suspension.

The need for a better bushing material is especially important to Corvette owners because camber loss at the rear will cause oversteer Figure Front Deflection Steer Rubber suspension bushing deflection can also have a dramatic effect on the steering characteris tics of your car. The steering linkage consists of rigid links and joints, so there is little deflection when these parts are loaded by high cornering forces.

When the front control arm bushings deflect, the control arms can move in relation to the frame. The cornering loads cause this deflection to result in positive camber, which reduces and distorts the tire patch. The net effect is a loss of cornering power at the front.

On the street, precise and predictable handling is the key to high performance driving. However, the art and science of engineering a chassis can be difficult to comprehend, let alone apply. Hundreds of photos and illustrations illustrate what it takes to design, build, and tune the ultimate chassis for maximum cornering power on and off the track.

Reviews of the Chassis Engineering HP Thus far regarding the publication we've Chassis Engineering HP suggestions users are yet to but still left his or her article on the sport, or otherwise see clearly still.