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Front Suspension and Slip Angles

The front suspension on a car is unique because you are free to steer the wheels. This gives you a certain level of control over what happens at this end of the car. So, as long as the tires have traction, you are free to steer the car and change your direction of travel. Or, in other words, if you steer the wheels to the left, the car will go to the left and if you steer the wheels to the right, the car will go to the right.  However, on circle tracks we usually want to go left.

However, the tire/wheel is not a rigid unit. The tire can flex (a lot) in relation to the wheel. Automotive engineers use the term "Slip Angle" to describe the difference in heading between the tire and wheel. A good way to illustrate this characteristic is to stand beside your car on the driver's side, reach in and wiggle the steering wheel. If you watch the left front wheel, you will see that it steers a few degrees before the tire's contact patch starts to turn. That difference in the wheel's angle and the contact patch is the slip angle.

Unlike the rear tires, if the front tires develop a larger slip angle, you are free to turn the steering wheel a little farther and still maintain the desired direction of travel. Technically, this is considered understeer, but you are still in control of the race car. Your car will have a distinct (springy) feeling and steering wheel position in this condition.

With larger slip angles, it will require more steering wheel angle to maintain the desired path through the corner. Smaller slip angles on the front tires will require less steering wheel angle to maintain the desired cornering line. But how can you change slip angles?

Tire loading directly impacts slip angles and in an unusual manner. At the front end, two equally loaded tires will run at smaller slip angles than two unequally loaded tires while in a corner. Increasing the weight transfer at the front of the race car increases the slip angles and tends to require a larger steering wheel angle (from the drivers view, the car may "push" in the middle of the turn). Likewise, reducing the weight transfer at the front end reduces the slip angles and requires less steering wheel angle (to the driver, this may seem to loosen up the rear end of the race car).

Items such as spring rates, spring locations, sway bar rate, all affect the weight transfer when your race car is the turns. This is where a program like Computerized Chassis Weights is a big advantage because you can experiment with changing these items in the computer and see how they affect the weight transfer.

Some of these changes only affect the weight transfer a small amount. Other changes, however, make a large change in the amount of weight that transfers from the inside tire to the outside tire. But, the simplest way to know how much weight is being transferred is with a computer program.

Keep in mind that these causes and effects are true as long as the tires have traction. If you drive on oil, or for some other reason your tires are already sliding, then you can pretty much forget the items above. Remember, racing can be dangerous. Always use your best judgment and the best tools!

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