Camber, Caster, and Toe
Camber, caster, and toe orientate the wheel to the chassis. This is how engineers determine how the rubber meets the road, quite literally. Tire loading in various travel attitudes are controlled by these setup parameters. How you set these alignment values will greatly influence your lap times as well as your mid- to late-run tire wear, temperatures, and traction. In the next section of this guide (“Tire Pressure and Temperature”) and the “Setup Procedures” sections of this guide, you will learn how to use tire temperature to adjust these values.
Camber is a measurement, in degrees, of how far outward the wheel leans. A positive number means the wheel is leaning outward, away from the centerline of the car; while a negative number means that the wheel is leaning inward, towards the centerline of the car.
Excessively cambered wheels take the wear load off one third of the tire. This effectively gives you 67% usable tire at that corner of the car, and it cannot do long green flag runs as well as a camber adjustment that makes the whole tire work.
Camber changes as the run goes on. Speeds slow and cornering forces decrease and the tire loading transfers from the left two-thirds onto the right third, allowing all three-thirds of the whole tire to work. If the wheel is insufficiently cambered, the tire loading will transfer too far over onto the right third (and off from the left third) toward the end of a long green flag run.
The key to a properly cambered wheel is to wear on all three-thirds of the whole tire for the most of the green flag run as possible.
Camber adjustments can usually be made to all four wheels. Too much camber can overheat the left third of tire and cause a loss of grip (looseness). Too little camber overheats the right edge of the tire and also causes a loss of grip. More camber lean in the direction of the turn increases the cornering forces, but decreases braking force and increases heat.
|Camber Adjustment||Cornering Force||Braking Force||Tire Heat|
For example: At the end of a run, your wheel temperatures may be:
272F 258F 192F
you can plainly see that the right side of this tire is WAY colder (192F) than the left side (272F). This means that the wheel is cambered too far to the left, and needs to be adjusted to put more weight on the right side of this tire to load it up and make it work.
To make a camber adjustment, first note the ride height at that wheel. Make the camber adjustment; then use the spring perches (sometimes called “shock collars”) to reset the ride height at that corner. This will help prevent camber adjustments from interfering with your chassis balance.
Adjusting cambers changes ride heights, which of course alter the tight-loose influences of that corner of the car. Do not use camber to change tight-loose conditions. Use camber to even out tire wear and temperature. You can use the garage averages at the end of your test runs for this, but it is far better to use telemetry.
As a front wheel turns with steering input, the bottom of the tire pivots at the point where it makes contact with the ground. Think of this as the “South Pole.” At “zero caster,” the “North Pole” might be straight up from there, at the top. This would be a caster angle of 0-degrees.
However, the “top” of the tire usually pivots at a point that’s a little farther back from that; say, the 1-o’clock position (if you were facing the tire from the outside of the car). This might be a 10.5-degree caster angle. The higher the angle, the farther back this top pivot point will be.
Leaning the steering axis back like this (with caster adjustments) has a number of interesting side effects.
- Contributes to oversteer while the wheel is turned into a corner
- Contributes to understeer while counter steering a slide
- Heavier feel in the steering wheel
- Camber leans farther left at the wheel/tire when turning left (e.g., while cornering)
- Camber leans farther right at the wheel/tire when turning right (e.g., while saving a spin)
Using a lesser caster setting on the left side than the right side helps the wheels to steer themselves to the left. This is known as “caster stagger.” This is because the left front wheel leans less to the left than the right front wheel; this leaves more of the front left tire in contact with the track compared to the right, causing it to pull harder on the left side than on the right. That helps the car steer down in and through the turns on an oval.
NOTE: Caster and cambers must be right before you can adjust the toe-in. This is because the tire temperatures may mislead you about your toe-in/toe-out adjustments if the camber in particular is not set accurately.
Toe-in means that the two wheels on the front (or the rear) of the car are pointed slightly inward. The more the wheels are toed in (positive toe-in values) or toed out (negative toe-in values), the more the wheels drag the track. The effect is slight, but present, and it affects tire temperatures. Toe-in is a micro-adjustment that won’t make or break a setup, but it will contribute greatly to driver comfort – especially in a long race.
Net toe-In is computed by adding the two values from the left and right sides; for example, the right front may be limited by chassis factors at -1/32, but you want your net toe-in to be +2/32. You would set the left front toe-in at +3/32, since +3/32 + (-1/32) = +2/32.
Excessive toe-in will result in higher outside tire temperatures. Insufficient toe-in (i.e., excessive toe-out) will result in higher inside tire temperatures. Again, tire temperatures will unmask this condition provided that the cambers are set correctly. This is explained in greater detail in the next chapter (“Tire Pressure”).
- Positive: Loosens turns, especially exit; steering wheel self-centers on straights
- Negative: Tightens turns, stabilizes exit
- iRacing recommends sticking to negative toe-in (toe-out) up front, but I run setups with toe-in up front for stability and driver comfort.
- iRacing recommends sticking to a positive toe-in in the back, but I try to run this at perfectly zero (which tech usually more or less requires anyways).
- Left toe-in coupled with right toe-out can create “side force” (aerodynamics which pull the car to the inside to allow faster corners; fails tech on some cars).