It's important to know how to properly measure for the amount of caster and camber in your race car. All teams need to learn the proper procedure for determining the amount of each that exists in the front end geometry of their cars.
Caster and camber settings are set relative to the type of car and the design of the racetrack. When you determine the correct settings for each, you need to maintain those settings. We will discuss what affects the caster and camber in our race cars, as well as how to properly measure them.
1. Positive caster in the front wheel assembly is created when the ball joints are offset,
Caster is a design condition that, in addition to the spindle king pin angle, serves to cause a wheel to want to track straight ahead. A common example is a bicycle front wheel and fork assembly. The tube that the handlebars are mounted to is mounted in a set of bearings above the fork and from a side view, this tube is angled so that the bottom bearing is ahead of the top bearing. If we turn the front wheel away from the direction of travel, it will want to return to straight ahead by the effect of caster. The same effect is present in the front wheel assemblies of our race car.
What Caster Does
To ease the amount of effort it takes to turn the wheel left in our circle track race cars, we introduce caster split into the design. Split means that we set different caster amounts into each wheel assembly so that the car will naturally want to turn to the left and thereby reduce the amount of effort it takes for the driver to hold the steering wheel when negotiating the turns.
Proper split for asphalt circle track racing means that the left front wheel will have less positive caster than the right front wheel. In some cases, teams have been known to set negative caster in the LF wheel and positive caster in the RF wheel.
For dirt racing, equal caster to minimum amounts of caster split are proper due to the fact that the wheels will be turned both ways as the car enters (left), corrects for rearend slide (right), and exits the turns (back to the left). So, the steering wheel must be more equal in steering effort for left and right turning for a dirt car.
2. To begine checking caster set the bubble at zero on the caster side of the gauge. Some
To measure caster in each wheel, we use a caster/camber gauge. This tool attaches to the wheel hub. To check the amount of caster, we need to follow these instructions:
- Attach the gauge to the RF wheel hub first.
- Turn the steering wheel to the right so that the right front wheel has turned exactly 20 degrees. You can use a turn plate that is graduated in degrees or measure from our illustration
- For a manual bubble gauge, level the gauge at this point and set the adjustable caster bubble vial so that the bubble is at the zero mark on the caster side of the tool. For a digital gauge, set zero once the wheels are turned and the tool is leveled.
- Now turn the steering wheel to the left so that the right front wheel is turned past straight ahead and ends up left of straight ahead by 20 degrees.
- Again level the gauge and then note the location of the bubble on the scale of the bubble gauge and record the amount of caster in the RF wheel. For a digital gauge, just level the gauge and read the display and that is the caster amount for the RF wheel.
- While the wheels are still turned left 20 degrees, remove the caster/camber gauge and place it onto the LF wheel hub. (Note: this wheel should be turned the same 20 degrees as the right wheel, but if you have Ackermann in your steering, it may have turned more than 20 degrees. If so, go to Step 2, reverse the directions and follow the procedure we used for the right front wheel.)
- Level the gauge and set the bubble on the caster gauge to zero or zero out the digital gauge.
- Turn the steering wheel to the right past straight ahead until the LF wheel is turned 20 degrees to the right of straight ahead.
- Level the gauge and read bubble scale or digital display to know how much caster is in the LF wheel.