In the world of race car setup, the frontend settings can become downright confusing. But there's much to gain by understanding caster, camber and toe settings, and how they can work together to make your race car go faster.
A side view of the car shows an imaginary line runs through the center of the upper ball joint to the center of the lower ball joint. This is known as the pivot line. If this line is absolutely vertical, then the caster measurement is zero, or no caster. When the top of this line is leaned toward the rear of the car, we now have positive caster.
Try pushing around a chair with casters on it. You will find it has no directional stability. This is because the casters have negative caster and want to follow the slightest force in any direction. Your race car should have positive caster to achieve that directional feel.
As opposed to some years ago, most race cars now have power steering. This allows the use of more caster.
In cars using stock or near-stock frontend geometry, caster can be increased from the factory settings. Caster stagger is also a useful setting. Caster stagger occurs when there is more positive caster on the right side than on the left. When entering a turn to the left, the excess caster on the right will give the car a natural tendency to turn left.
Long tracks, especially the paved ones, need only a small amount of caster stagger perhaps only 1 degree. At a ¼-mile dirt bullring, much more can be an advantage. The IMCA stock car we recently put together in Stock Car Racing uses 9 degrees of caster on the right and 5 degrees on the left. This is a lot, but the car turns in easily.
Setting caster is easily done with a gauge built for that purpose. Most of the store-bought units screw on or magnetize to the front hub. Turn plates are then placed under the front wheels. The wheels are steered a certain number of degrees each way. The gauge will then read the caster in degrees. This type of gauge may be necessary with aftermarket rod ends.
Lots of caster stagger is ideal on a small dirt track. Get all the caster the right side will allow with the correct amount of camber. Then adjust the left-side caster using enough caster stagger to give you the feel you want entering a turn. Start with a lot and then take it out if you don't like it.
Another setting for the front suspension is camber. Camber is measured at the wheel, not the ball joints. A frontal view of the car, when the wheel is straight up (no lean), shows the wheel has no camber. When the wheel is leaned in at the top toward the center of the car, it has negative camber. Therefore, when it leans out at the top, the wheel has positive camber. Race cars can use both positive and negative camber settings to their advantage.
Camber is a very visible part of the frontend settings. We have all seen the right front leaning toward the center of the car. Sometimes this is severe enough that the outside of the tread is not touching the ground. This much negative camber reduces the traction at the front of the car. If the car seems balanced in its handling with this setup, then the suspension is crippled somewhere else.
Only the right amount of camber will net maximum traction. Selecting the right amount is determined by the built-in suspension design. All the suspensions we deal with have camber gain. When the wheel goes up in relation to the chassis, which is called bump travel, the camber increases, or gains. Camber is designed to reduce the effect of tire flex. Camber gain also adjusts for suspension movement. Together, they work to keep the tread surface flat on the track. The big question is how much do you need.
The tire needs about 1 degree to start with. With most suspensions discussed here, there will be a gain of 1½ degrees to 2 degrees per inch of bump travel. If your suspension has 3 inches of bump travel, that would add up to 4½ degrees to 6 degrees. Add in the 1 degree negative initial setting and you have 5½ to 7 degrees negative at full travel.
This is best accomplished by blocking the chassis and removing the spring. Then the suspension can be cycled with a jack. Set the camber at full bump travel. The car should be level. Then with the spring replaced and the car on its wheels, measure the camber. From now on that will be your static camber setting on the right front.
A problem with some stock suspension mountings is not allowing all the caster needed while providing enough camber. Split the settings, if necessary, by removing a degree of caster and a degree of camber. Just keep the caster stagger the same.
Camber on the left front will not be the same as on the right. You will need positive camber on the left front wheel. There is little camber change as the left front goes down, the reverse of bump travel. Therefore, an initial setting of ½ to 1 degree positive camber will work well.