Camber and toe: grip now against tyre life later

Camber and toe are the two adjustments that trade grip in one phase of a corner against grip in another, and both are judged by tread temperature rather than by feel. Both are also the settings most often copied from somebody else's car, where they mean something different.

What camber does

The guide defines it as an alignment measurement of how much the top of a tyre is tilted in toward or out away from the centre of the car, and notes that adding negative camber, for example from minus 1.0 to minus 2.0, tilts the top of the tyre in. The purpose is named too: camber optimises the tyre's contact patch as the car rolls toward the outside of the corner at maximum load.

That is why camber changes are most effective at mid corner. Adding negative camber at the front should help grip at the apex; adding it at the rear does the same for the rear. The compromise is that the negative effect of adding camber shows up in a straight line, where less of the tread is on the ground and therefore less performance is available.

Both ends have their own failure mode. Too much negative camber at the front can cause a snap understeer slide, described in the guide as similar to hitting a patch of oil. Too much at the rear may cause snap exit oversteer and excessive tyre wear. Both arrive suddenly, which is what makes over cambering expensive.

What toe does

Toe is the direction the two tyres of an axle point relative to the centreline of the car. Pointing in gives positive toe, or toe in; the amount is measured in fractions of inches or in millimetres, represents deviation from zero and is cumulative across the axle.

A small amount of positive toe is useful because the two tyres working slightly against each other keeps the car stable over slight imperfections in the road. The guide notes that most cars have a baseline with one axle running positive toe and the other negative.

At the front, toe in increases stability in the braking zones and slows the response to the initial turn of the wheel, with increased scrub slowing straight line speeds as the compromise. Toe out has its largest effect at corner entry by speeding up the response to the initial turn, and the tradeoff is straight line speed and stability.

At the rear it changes the whole corner. Toe in points the loaded outside tyre slightly toward the apex, which helps rear grip and overall stability. Toe out points it outward, and the guide is blunt about the result: the car rapidly transitions to oversteer as the grip limit is reached, so rear toe out is generally only used to combat a significant understeer condition that cannot be addressed otherwise.

Reading the temperatures that judge them

Camber is judged by the spread across the tread, and the guide gives the target: about 10 degrees of differential from outer to inner edge, plus or minus 5, with the inner edge hottest. An outer edge far hotter than the inner means not enough negative camber; the reverse means too much.

Toe is judged by tyre wear and by straight line speed rather than by temperature alone. Excessive scrub from too much toe shows up as a top speed that does not match a car with the same power, and as tyre temperatures that are high everywhere rather than high at one edge.

And both are judged over a stint rather than a lap. Camber that is optimal on lap two is often too much by lap thirty as the tyre wears and the pressure rises, which is the practical meaning of grip now against tyre life later.

Setting them without copying

Count the settings before you touch them. 4 camber values and 4 toe values is 8 numbers, and at 3 positions each that is 6,561 combinations. In practice only 2 of the 8 matter on most road cars, front camber and front toe, and 5 laps per test means 8 tests in a 40 lap session. Change 1 of the 2 that matter and you have an answer; change 4 and you have a different car and no answer.

Start from the default and change one end by one step. A camber value copied from somebody else's setup is the answer to their spring rates, their bar settings and their driving style, and it will produce a different tread temperature spread on your car.

Then verify with five laps and the temperature readout rather than with feel. Camber changes are almost invisible in a single corner and obvious in the numbers, which is the reverse of most setup adjustments.

Sources

1. iRacing, official car setup guide
2. iRacing, in game meter box and telemetry readouts

Frequently asked questions

How much negative camber should I run?

Whatever brings the tread spread to about 10 degrees, plus or minus 5, with the inner edge hottest. The number itself is meaningless without that check.

Why does more camber make the car slower on the straight?

Because less of the tread is on the ground when the car is upright, so less performance is available where the tyre is not loaded sideways.

Is rear toe out ever right?

Only against a significant understeer condition that cannot be addressed otherwise, and with the knowledge that the car will transition to oversteer rapidly at the limit.

Can I copy camber values from a fast driver?

Not usefully. Their value answers their springs, bars and style, and on your car it will produce a different temperature spread.