It’s best to use a digital...
It’s best to use a digital gauge to measure your turn angles. Turn the wheels to the right from straight ahead so that they turn 20 degrees. Then level the gauge or push the “zero” button to set zero in the display. Then turn back to the left to 20 degrees past straight ahead and read the gauge for caster.
If you have permanently attached vertical mounting plates that the upper control arms are attached to, then you can vary the amount of shim spacing for each of the bolts that attach the control arm to the chassis. 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 degree of 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.
Normal caster splits for most short track asphalt applications are around 2-4 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 split that is needed because less steering effort is needed due to the banking. The tighter the turn radius, the more caster split that is needed.
Change the thickness of the...
Change the thickness of the adjustment shims at the front and back at each mounting bolt, or slide the control arm shaft, if it’s slotted, to adjust the amount of caster in each wheel. This will move the upper ball joint forward (to reduce caster) or to the rear (to add caster).
For dirt applications, smaller numbers are used because of the need to steer both left and right in many cases. Less overall caster angle and less split, or no split, is normal. A caster split as described above would require more than normal effort to turn the steering wheel right and would feel unnatural to the driver.
Camber and Camber Change
Camber is when a wheel is tilted so that the top of the tire is a different distance from the centerline of the car 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 of the tire. Positive camber is when the top of the tire is farther away from the center of the car than the bottom of the tire.
In circle track racing when turning left (in some countries cars turn right), 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 reading the digital readout for those types.
From a driver’s view, the...
From a driver’s view, the positive left front camber causes the top of that tire to lean out away from the centerline of the car. The opposite is true of the RF tire which has negative camber. On that wheel, the top of the tire leans in toward the centerline.
We have learned some interesting and important characteristics of tire camber for short track racing. 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 the amount of tire roll is different.
Tire temperatures tell us a lot about how much static camber we ultimately need so that the tire contact patch will be optimal at mid-turn. 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 grip it's 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's the RF wheel.
The cambers will often change as the car dives and rolls as it enters and negotiates a turn. True camber change is a product of both chassis dive and chassis roll. Gone are the days when we would jack up the wheel and measure how many degrees the camber changed in each inch of bump. Those numbers really don't tell us anything.