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Toe in or Toe out ? that is the question.

First, let's define what we mean by toe. It is the difference in the distance between the front and rear edges of the rims on one axle. If the distance at the front is larger than the rear, then the alignment is said to be toed-out, and if the distance at the rear is larger than the front, that's toe-in. This is relatively easy to measure and to adjust. It requires not much more than a tape measure, or an alignment rack, and then loosen the jam nuts on the tie rods and adjust the rods.

Having said all that, what does toe-in or toe-out do to the way a car handles. Generally the rule of thumb is that more toe-in increases understeer and more toe-out increases oversteer. However, with modern cars, especially race cars with independent front and rear suspensions, there is another effect on handling. Most manufacturers recommend a chassis alignment which contains a small amount of toe-in. This will give the best possible stability at speed; the car will not have a tendency to wander. And the small amount of toe actually pre-loads the wheel bearings to make turning more instantaneous.

But what does toe-in do to the handling of a race car. As soon as you turn the wheel, the front tires initiate the turn and the rears simply follow. Therefore, what happens at the front wheels will determine how the car responds to the initial steering input. When cornering, the outside tire requires a larger turning radius than the inside tire. In other words, the inside tire has to turn more sharply than the outside tire to get the maximum combined cornering force. With a car that has toe-in, the inside tire is constantly turned in, and it is fighting the outside tire and detracting from the total front cornering power. This reduces the ability of the front end of the vehicle to turn into the corner. However, by having the front wheels set with a small amount of toe-out, the instant you turn the wheel, the action of the inside tire turning more sharply than the outside tire already exists and the car turns into the corner "like it is on rails". Once the car gets turned into the corner, then the weight starts to transfer from the inside to the outside, thus minimizing the effect of the inside front tire. Also then the rear tires are contributing to the overall cornering power while the suspension components (springs, shocks, roll-bars) are reacting according to their designs and settings.

So if your race car just does't like to turn in, and you feel as though you have to literally throw the car into the turn to get it to turn in, try a small amount of toe-out, rather than the conventional toe-in. You will lose a little amount of straightline stability, but the car will certainly turn in much better.


Tech Tips Archive

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Toe in or Toe out

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