Camber, Caster & Toe
Corvette Wheel Alignment Decoded
Camber, caster and toe are terms used to describe the alignment settings of your Corvette’s suspension system. These three settings have a major effect on the driving characteristics of your car and how your tires wear over time. While these terms are familiar to all of us, I thought it would be helpful to define them and show how they influence the drivability of our Corvette. This discussion will give you a great baseline of information and allow you to have very good dialogue with your alignment technician.
If you look at your Corvette from the front or the rear of the vehicle, camber is the inward or outward tilting of the wheels with respect to vertical. On a Corvette, the wheels tilt inward at the top, which is known as negative camber. Camber is measured in degrees from vertical and is adjustable for both the front and rear suspension. Camber settings influence directional control and tire wear. For autocross or road course Corvette, higher negative camber values are dialed in. When your car is turned fast at speed, as in autocross events, or driven hard through a turn on a road course, physical forces on the car will cause some body roll. This body roll works the suspension and to some extent causes the wheels to go to a positive camber value. As this occurs, there is a less effective contact patch of the tire to the pavement. This means less effective grip between the tires and the track.
When utilizing larger negative camber values, what you are trying to accomplish is to preload your tire / rim to a state where, when cornered aggressively, the physical forces on the wheel will put it in a nice vertical orientation with the pavement. What that will give you is a maximum tire contact patch and maximum surface grip. When driving in a straight line, a negative camber tire will not have 100 percent surface contact, but that is okay. You need the additional grip in corners or when turning sharply and your overall track times should improve from this. Generally, a Corvette with softer suspensions (stock suspensions) will benefit from higher negative camber values than cars with stiffer (Z51) suspensions. This is due to the higher body roll rates experienced when working the suspension hard on lighter spring rate / softer shock / smaller sway-bar base Corvette.
Caster is more difficult to describe. Imagine looking at the side of your Corvette so that you can view your left front wheel. If a vertical line is drawn through the center of the rim and the vehicle weight is directly at the bottom of this line, with the line equally bisecting both the upper and lower ball joints, then caster is considered to be zero. A Corvette has positive caster, which means the lower ball joint is positioned forward of the upper ball joint. Technically, this means there is a rearward tilt of the line (steering axis) at the top with respect to vertical. This actually positions the vehicle weight directly under the upper ball joint, which on the example of your left front wheel means the vehicle weight is to the right of (behind) the true vertical centerline of the rim itself. Caster is measured in degrees and can only be adjusted for the front suspension. Caster angles can influence directional stability (straight line), steering effort, and cornering traction. Caster and camber work together. Caster does not impact tire wear.
Toe measures how much a wheel is turned in or out from a straight ahead position. When wheels are turned in, this is considered “toe in” and is referenced as a positive value. If the wheels are turned out from straight ahead position, this known as “toe out” and is stated as a negative value. Toe values on a Corvette can be adjusted for both the front and rear suspension of the car. Keep in mind toe is a cumulative (combined) value for both the left side and the right side of the car. This is known as “total toe.” Generally, toe is set as a symmetrical value, meaning the technician should strive to make the left side reading the same as the right side reading. Correct toe settings help ensure the wheels roll parallel and serve to offset small steering deflections as the car travels forward. Toe settings can also be adjusted to enhance steering response and aid corner turn-in. Toe does affect tire wear.
I’m an old school mechanic, so I use fractions of an inch to describe toe values. For example, a Corvette may have a rear total toe value of an 1/8-inch. Each side therefore is set at 1/16 inch (1/16 inch x 2 = 1/8 inch). The new alignment machines, such as those manufactured by Hunter, are typically set up to measure all alignment angles in degrees. The machines will measure toe in fractional inches, but I wish you good luck in finding a technician that knows how to toggle between the two different systems. It is much easier to give the technician the value in degrees, especially if you are adjusting your Corvette outside of normal street-use parameters.
Here is what you need to know: degree values are not equal to inch values - for toe purposes, degree values are double their inch counterpart. If you desire an 1/8-inch total toe in, then you need to inform the technician that you want the total toe to be set positive at 1/4 degree. Since each side has to be independently set, your 1/16 inch (0.0625”) equals 0.12 degrees. The alignment machines will not run out to thousandths of degree, so 0.125 degrees can’t be dialed in. You can ask for 0.12 degrees. Therefore, you will receive a total toe setting of positive 0.24 degrees, equivalent to 1/8 inch (0.12 inch) of total toe-in.
For street cars and the type of NCCC racing we do, camber and caster settings should be identical or as close to identical as possible for left and right side values. The measurement terms used to describe this are known as cross camber and cross caster. There are certain parameters for these values to fall within. For example, on C4’s the front cross camber is +/- 0.5 degrees. If you desire your front negative camber to be 1.5 degrees and that is your driver side value, then the passenger side value should be between -1.0 and -2.0 degrees. If your technician takes a little extra time, he should be able to get the two sides within a tenth of a degree of each other. On occasion, I have been able to set the values to be identical to each other. For C4 or earlier generation cars that utilize shims for adjustment, this does take some patience and extra time.
An excellent (and free!) resource for various alignment settings on C2 - C5 Corvette is Vette Brakes and Products website, www.vbandp.com. Go to the Instructions tab at the top of the home page, select Corvette and then click on “Alignment Specifications” under the documents section. Here you will find some great suggestions for the alignment specifications discussed in this article. Figures are given for street, autocross and track cars.
In closing, I prefer to use Chevrolet dealerships to do my Corvette alignment settings. They typically have the newest and latest technology Hunter alignment machines. These alignment units can accommodate lower Corvette cars and C6 Corvette. Some independent shops either can’t get the car on the track without tearing up the lower air splitter, or they can’t read toe values because the cars sit so low. Finally, always request “before” and “after” alignment values. That way you can see what alignment changes were made and that the final settings agree with your target values.
Reprinted from Sportsmate May 2013, the official publication of the Corvette Club of Iowa, www.corvetteclubofiowa.com.