Camber Crutches

Written by on June 18, 2004 Unusual camber settings can be an indication of a race car that needsattention to geometry design or changes in the basic setup.
Camber Crutches View All 12 Photos
0401139 Z+Dirt Late Model Race Cars+Front View Turning 1/12 Keys to camber change come when the car drives through the center of theturn. Camber changes can mask bigger issues.





139 0401 Crut 1 Z 2/12 Examples of Positive and Negative Camber






Before we get into the specifics of what makes up the best design for a particular track, it is important to understand some basic information about why the cambers change in your race car. Here are the five most important effects that cause camber change:

1. Magnitude of chassis roll

2. Magnitude of chassis dive

3. Control arm lengths

4. Control arm angles

5. Spindle height

Roll Angle As the car enters the turns, two things happen to affect camber change. First, there's the action of the front wheels. The right front wheel is always in bump (moves up in relation to the chassis), and the left front wheel either stays close to the same position (as is the case with most late models on moderately-banked racetracks), in rebound (moving down in relation to the chassis normally associated with dirt cars using very soft right rear springs), or in compression (when the track is very high-banked with lots of grip).

139 0401 Crut 2a Z 3/12 (above & right) We can learn to look at a tire and see the approximate degree of camber.The tire on the left is at around 31/2 degrees of camber while the tireon the right is at 6 degrees of camber.
139 0401 Crut 2b Z 4/12

Another thing happening, that is often ignored, is that the chassis itself is rolling. As the chassis rolls, the upper chassis mounts are moving to the right (in a left hand turn). If the chassis mounting points are moving, so are the control arms as well as the upper ball joints. If the upper ball joints move laterally in relation to the lower ball joints, we have a change of camber caused by chassis roll.

Dive As the car dives, the upper ball joints are drawn in towards the center of the car. The lower ball joints are either drawn in or pushed out, depending on location of the chassis mounts (lower or higher than the lower ball joints). Because the lower control arms are longer and have less degree of angle than the uppers, the amount of camber change effect is much less. The upper arms have the greatest influence because of their amount of angle from horizontal.

Both of the front wheels will gain negative camber (top moving inwards toward the center of the car) as the car dives. At high-banked, high-downforce tracks, there is much more dive than roll. Close attention should be paid to the amount of camber change due to chassis dive.

Now, we can understand that if we try to determine the amount of camber change by bumping the wheel with the car at static ride height, we will not see a true picture of our camber change characteristics. The true camber change, relative to the racing surface, results from a combination of roll effect and dive effect measured together in combination.

Upper Arm Lengths The lengths of the upper control arms will influence the amount of camber change that occurs in each front wheel. The correct arm lengths for your car will depend on the overall design of the front end relative to the racetrack where you intend to compete.

The best way to know how the length of the arms will affect the camber change in your car is to use a geometry software program. This will allow you to install different-length arms without changing the arm angle. You can see the camber change effects that different lengths have in order to decide which length arms are best for your car.

Shorter arms affect more camber change from chassis dive. Longer arms affect more camber change from chassis roll. There is an optimum length control arm associated with camber change for each side of the car.

Arm Angles The angle of the control arms has a large effect on camber change. The upper control arms affect camber change much more than the lower control arms. The smaller the angles (from horizontal) that the upper control arms have, the less camber change that will result from chassis dive. A chassis with less upper control arm angle will also have more camber change resulting from chassis roll.

139 0401 Crut 3 Z 5/12 The static left-front wheel camber used on ultra-high banked tracks isusually very high, in the 4-5 degree range, due to the extreme amount ofcamber loss due to chassis dive. These cars roll very little andcompress up to 4 inches or more at tracks like Daytona. There are somevery high-banked dirt and asphalt short tracks where a similar situationexists.

The opposite is true of higher angled upper control arms. The degree of angle we have in the upper control arms will influence the amount of camber change. Optimum control arm angles are determined mostly by using the correct dive and roll numbers and simulating the attitude of the car at mid-turn. We can do this mechanically or with the use of a computer program.

The left wheel will always lose two degrees of camber or more due to the roll effect. There is no known design that will help this camber change and still have us maintain a correct moment center design. To even approach this goal, the left upper control arm would have to have around 45 degrees of reverse angle with the chassis mount higher than the ball joint. We would never do this to our race car, so we live with the left wheel camber change.

Spindle Heights The spindle height affects the amount of camber change in our race cars. The height of the spindle is the measured distance between the centers of rotation of the upper and lower ball joints. Spindles come in many different heights. What is generally true is that the greater the spindle height, the less camber change that will result from dive and roll.

It is reasonably easy to understand this. If the upper ball joint moves laterally one inch, the spindle will change its angle more with a 10-inch spindle than with a 12-inch spindle. The greater the distance between ball joints, the less angle that is produced with the same amount of upper ball joint movement, therefore, the less degree of camber change.

139 0401 Crut 4a Z 6/12 (above & right) The camber change characteristics can be adjusted by changing the angleof the upper-control arms. We usually adjust the right upper control armangle until we get zero change in camber after dive and roll. We thenadjust the location of the moment center, using the angle of the leftupper control arm. Upper-control-arm mounting plates using offset-holeslugs make changes to arm angles fast and easy. Slotted plates foradjusting caster do not allow angle changes. Control arm shafts withslots for caster adjustment are available to use in conjunction with theslugged upper plates.
139 0401 Crut 4b Z 7/12

How do we put all of this information together into a design for a front end that we can use? Let's draw some simple conclusions.

As a rule, a flatter track will produce more of a chassis roll angle with less chassis dive. As the track banking angle increases, the amount of chassis roll decreases and the amount of chassis dive increases due to more downforce effect. The overall goal here is to produce the least combined camber change in each wheel, and especially the right front wheel, for each type of racetrack.

High Left-Front Camber Change The left-front (LF) wheel will always lose most of its positive camber as the car negotiates the turn. We need to end up with some amount of positive angle in the LF wheel after dive and roll. If the chassis rolled three degrees and the LF suspension did not travel at all, the camber change would be three degrees. We can simulate that at the shop by dropping the right side of the car to create 3 degrees of roll. The LF wheel will lose 3 degrees of camber.

139 0401 Crut 5 Z 8/12 Results of Chassis Roll

Zero Right-Front Camber Change The right-front (RF) wheel will either gain or lose negative camber, depending on the arm angles and lengths. What we really want is minimal gain in the negative direction at the RF wheel, and we never want the RF wheel to change camber in a positive direction. This way, we can maintain the same negative camber in the middle of the turn, after the car dives and rolls, that we had at normal ride height.

From extensive testing, we have determined that the RF tire likes this condition. It takes a set fairly early on entry to the corner. If the camber continues to change after that point, the tire tends to give up traction. If the camber remains the same during entry and through the middle of the turns, we can easily see incorrect camber settings by looking at the tire temperatures. Excess camber change can give false indications of the tire temperatures that we use to insure ideal camber settings.

139 0401 Crut 6 Z 9/12 Results of Chassis Dive

At the LF, we want to lose as little positive camber as possible so that we can start with the least amount of static positive camber. You will need to have about one-half to three-quarters of a degree of positive camber remaining in the left front wheel after the car dives and rolls. For both front wheels, the final tuning for the best static cambers is done by running the car and measuring the heat across the tires. Be sure to also look at the tire wear to help determine the best static cambers.

Excess Weight Transfer = Bad Setup The setups we run have a lot to do with our need to run excess RF camber and lower amounts of LF camber. The greater the force and weight put on a tire, the more that tire will deflect at the contact patch and the more static camber the car will need in order to maintain a solid footprint.

A setup where the two suspension systems, front and rear, are not balanced will cause excess weight transfer at the front of the car to the RF tire. In extreme cases, the RF tire will have to support the entire weight of the front of the car. Proof of this is when we see a car carry the LF tire off the track surface. At that point, the RF tire supports the entire amount of front weight.

139 0401 Crut 7 Z 10/12 Spindle Height Effect on Camber Change

There are varying degrees of this excess weight transfer, and we do not always see light under the LF tire. We need to maintain a more balanced setup so that the LF tire will share the load and help work to turn the car so the RF tire does less work, and therefore, will require less static camber. Low angle of camber in the left front is one of the indicators of excess weight transfer. We look at the tire temperatures and see where the inside of the LF tire is hot, then we take positive camber out of that tire. With an unbalanced setup that transfers excess weight to the RF tire, there is less force acting on the LF tire, and so less static camber is needed because that tire is doing less work.

Tracking Moment Center Throughout this whole process, don't forget to track where moment center is located from the centerline of the car (halfway between the two tire contact patches), and keep it in its proper location. The height of the roll center will change slightly as you increase or decrease the upper control arm angles. You can change arm angles and arm lengths, and still keep your correct moment center location.

The front end geometry software will allow you to make the correct changes to arm angles so the moment center distance from centerline does not change. As we have learned in the past, the location of the moment center in relation to the centerline of the car is critical. Do not start changing arm angles and lengths without tracking how each change affects your moment center location.

139 0401 Crut 8 Z 11/12 You can set your static camber at the shop by using a solid adjustablelink in place of the shock. You will need to know the shock length whilethe car is at static ride height with all of the weights in the car,including driver. You can adjust the length of the link to fit the shocklength and set the camber before going to the track.
139 0401 Crut 9 Z 12/12 Taking tire temperatures tell us a lot about where our static cambersshould be set. If the geometry is correct with minimal camber changeafter dive and roll, we can believe our tire temperatures and makeadjustments to improve traction. If the camber is changing dramaticallyafter dive and roll, then we will be crutching the static camber to tryand solve the problem.

How important is camber change in the overall scheme of things? To give you an example, I have seen front-end designs that produced 51/2 degrees of camber change at the right front wheel on a 12-degree banked racetrack. From straightaway to mid-turn, the tire went from 31/2 degrees of negative camber to 2 degrees of positive camber. Oddly, the tire temperatures looked fairly normal. Every part of the tire was being worked, but not at the same time. In this case, the tire was working the inside on entry, the middle at quarter-turn (they added excess pressure because the middle initially was cool), and the outside at mid-turn. However, the car pushed because it never had a chance to use 100 percent of the RF tire's contact patch.

If this team, or for that matter the guy who built the front clip, had a good geometry program, they could have seen what was happening with the front cambers. Some car builders draw the front ends out on paper to establish the moment center location, but it doesn't tell them what is happening as the car dives and rolls in the turns.

This is a whole new age in racing. You can now get the most traction potential out of your front tires by making sure the front end design is correct for camber change and moment center design, and that the setup is balanced so that both front tires will share the load in the turns. When these elements are correct, it will make a huge difference in the performance of the front of the car. It will also determine how close to the front you finish at the end of your race.


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