In our first installment of this Setup guide, we explained the primary goals and all of the parts and pieces connected with the basic setup of your race car. We explained the relationship of the two suspension systems—front and rear—the mechanics of each, and how they need to work together. In this, Part 2, and in the final Part 3 next month, we'll examine the other areas of the race car design that could possibly affect and upset what we accomplished in Part 1.

Even though we select the perfect combination of springs, moment center locations, and weight distribution for our car for the type of racing we do, it still might not be enough and seldom is. There are other influences on the handling of the car that need to be addressed and perfected before we can truly say we have a car capable of winning.

The geometry of our suspension systems aside from the moment centers is critical to how the car will roll around the track and how much grip will be available from our tires. There are five areas we will cover beyond Part 1 and those include: 1) caster and caster change, 2) camber and camber change, 3) bumpsteer, 4) toe settings and Ackermann, and 5) rearend alignment and rear steer.

It's very important to address each of these items in the order presented. Each can influence others and when we work in this order, we make sure not to get one thing ahead of any others that may affect the former step. For this part, we will cover the first three.

Caster Split and Caster Change
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 so that the fork places the wheel axle and the point of the tire that touches the ground ahead of the part that rotates. From a side view, a line running from the top of the assembly to the tire contact point is angled, much like the spindle on a race car. 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 due to spindle caster inclination.

To ease the amount of effort it takes to turn the wheel in our race cars away from straight ahead, we introduce caster split into the design. Split means that we set different caster amounts into each front wheel assembly so that the car will 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. For dirt racing, we require less caster split, or in some cases, none at all.

Proper split for circle track racing means that the left front wheel will have less positive caster than the right front wheel. Positive caster is when the top ball joint is aligned to the rear of the bottom ball joint. In some cases, teams have been known to set negative caster in the LF wheel and positive caster in the RF wheel to affect the split.

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 specific procedures. Refer to our illustrations for tips on how to do this correctly.

To adjust the amount of caster in each wheel, you'll need to move the upper ball joints, and in some cases the lower ball joint, fore or aft. To increase the amount of positive caster, move the top ball joint toward the rear of the car, or the bottom BJ toward the front. Some cars have slots cut into the upper chassis mounts for this purpose.