Adjusting caster

To adjust the amount of caster in each wheel, you will need to move the upper ball joints fore or aft. In rare cases, you can also move the lower ball joint. Just reverse the following instructions when moving the lower ball joint. To increase the amount of positive caster, move the top ball joint toward the rear of the car. Some cars have slots cut into the upper chassis mounts for this purpose.

If you have permanently attached vertical mounting plates that the upper control arms are attached to and do not have slots, then you can vary the amount of shim spacing for each of the bolts that attach the control arm to the chassis to move the ball joint. Wider spacing at the front bolt (control arm shaft inside of the mounting plate) will move the upper ball joint to the front creating less caster at that wheel and so on. This is not the preferred method though.

Once you have established the exact caster amounts for each wheel using the above method, (if not using slotted control arm shafts) you should order an upper control arm that has the ball joint offset to give the correct amount of caster at each wheel. That way, you can use the same shim spacing for each mounting bolt to connect the upper control arm shaft to the chassis.

How Much Caster Split?

Normal caster splits for most short track asphalt applications are around 2 to 4 degrees of difference. The LF caster might be 1-2 degrees and the RF caster might be 3-5 degrees. The higher the banking angle of the racetrack, the less caster that is needed because less steering effort is needed due to the banking. Also, the tighter the turn radius, the more caster split is needed. Driver preference plays a big part in getting the caster split right for your application.

If you decide to run negative caster at the LF (meaning the upper ball joint is ahead of the lower ball joint), the split will remain the same to achieve the right amount of turning assist.

Camber Defined

Camber is when a wheel is tilted so that the top of the tire is either closer to the centerline of the car or further from it than the bottom of the tire. Negative camber is when the top of the tire is closer to the center of the car than the bottom. Positive camber is when the opposite exists, the top of the tire is farther away from the center of the car than the bottom of the tire.

In circle track racing, turning left we use positive camber on the LF wheel of the car and negative camber on the RF wheel. We can easily check the amount of camber by using a caster/camber gauge and reading the amount directly on the camber bubble vial or the readout on a digital gauge.

We have learned some interesting and important aspects of tire camber for short track racing over the years. We have always known that a racing tire will flex under the stress of cornering and the tread will move and roll under the wheel when the extreme forces associated with cornering are present. Different brands of tires have different stiffness of sidewall construction and therefore roll over more or less.

Tire temperatures tell us more about how much static camber we need than anything else. The overall goal is that we need the tire contact patch to be relatively flat on the racing surface at mid-turn in order for the tire to be able to provide the maximum amount of traction it is capable of giving. This is often referred to as the maximum “footprint.”

Tire temperatures can alert us to improperly set static cambers. A front tire that is hotter on the inside edge (side toward the inside of the racetrack) usually has too much positive camber in the case of a LF wheel, or too much negative camber if it is the RF wheel.