Understanding Caster, Camber, Toe, and Ackerman

Caster Explained

To understand caster you need to picture an imaginary line that runs from through the upper ball joint and extends through the lower ball joint. From the side view the imaginary line will tilt forward or backward. The tilting of this imaginary line is defined as caster.

Caster is measured in degrees by using a caster camber gauge. If the imaginary line described above tilts towards the back of the car, at the top, then you will have positive caster. If the imaginary line tilts forward then you would have negative caster.

Positive caster provides the directional stability in your race car. Too much positive caster will make the steering effort difficult. Power steering will allow you to run more positive caster. Negative caster requires less steering effort but can cause the car to wander down the straightaway.

Camber Explained

Camber is the tilt of the tire as viewed from the front of the car. If the top of the tires lean toward the center of the car then you have negative camber. If the top of the tire tilts out away from the center of the car then you have positive camber.

Camber is measured with a caster camber gauge and is usually easily adjusted with shims or adjustable upper a -arms. Always check the toe when making camber or caster adjustments.

Toe - In Explained

Toe is the pointing in or pointing out of the front wheels as viewed from the top of the car. If the front wheels point in, toward the front of the car, at the front edge of the wheels then you have toe in. If the front wheels point out at the front edge then you have toe out.

In general, dune buggies and race cars are set with a small amount of toe out. The toe out provides directional stability. Toe out pulls on the tie rods taking out the tiny clearances that are built into the tie rod ends. Depending on the type of car typical toe readings are 1/16" to 1/4" out for tracks under 1/2 mile in length.

Toe can be set with a tape measure on the side walls of the tires. A tape is placed on the inside front of the tire as near the rim as possible or pick a good location on the tire tread if possible! (As close to center horizontal as possible) and then measured in the same location on the front edge of the other front tire. Remember to measure from the same locations each time you check the toe. Now check the rear side of the front tires as close to the center rear of the tires as possible. If this number is a smaller tape reading on the back edge this indicates toe out.

For a very precise reading you can scribe a line in each front tire. Use a tire scribe and spin each of the front tires to get your straight line. You can then measure between the two scribed lines with a tape measure or with a toe bar or with toe plates, a smaller measurement at the backside of the tire again, indicates toe out.

Ackerman Effect Explained

Ackerman is the difference in turn radius between the front tires. On oval track cars it can be desirable to create a situation where the left front tire turns faster than the right front tire. The Ackerman effect can help the car turn better through the center of the turn. You can measure the amount of Ackerman you currently have by using a set of turn plates. Typically, Ackerman is measured by turning the right front 10 degrees to the left. If you have Ackerman, the left front will travel further than the right front. A typical amount would be three degrees in 10 degrees of steering. To simplify, moving the right front from zero through 10 degrees of steering will cause the left front to move say 13 degrees in this scenario.

Ackerman is created by your front end geometry. Tie rods that angle forward from the inner pivot point out to the spindle will have more Ackerman.

Writeup by DieselJeff

Last Modified: 7-13-05 JCH