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Chassis Set-up At The Rear For Cornering

As long as the tires have traction, the car tries to go where the wheels are pointed. If you steer the front wheels to the left, the car goes left. Likewise, if you steer the front wheels to the right, the car goes right. However, a change in the race car's direction can result from the front wheels steering or the rear wheels steering.

Just like the steering axle on the front of a toy wagon, the rear axle in a stock race car or modified can have the same steering affect. This is why rear suspension geometry is important with regards to how the car handles. For example: if the rear axle steers when the body rolls in a turn, then it will influence how the car handles in the turn.

Very small amounts (a fraction of one degree) of rear axle steer can make a big difference in how your race car handles. What makes it really tricky is that your car can have axle steer during braking, acceleration and/or body roll.

Ignoring this characteristic can lead to confusion and frustration. However, evaluating and controlling axle steer can be rewarding in how well your race car handles. Programs like the Rear Suspension Geometry software are a valuable tool in eliminating the confusion and taking charge and improving your handling.

Intentionally adding a small amount of roll oversteer can help a race car that pushes in the middle of the corner. However, a car that is loose in the middle of the turn may have too much axle oversteer. The simplest and least expensive way to know for sure if axle steer is aggravating or helping a problem is to use a computer program.

Something to also keep in mind is that the tire, wheel, and axle are not a rigid unit. The tire can flex (a lot) in relation to the wheel/axle. So, it should be said that, "As long as the tires have traction, the car goes where the tire's contact patchs are pointed."

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.

Like the front tires, your rear tires will have slip angles, too. The slip angles on the rear tires can affect how your race car handles, just like the rear axle steer. Larger slip angles on the rear tires tend to loosen up the car. Smaller slip angles tend to tighten up the rear end of the car. But how can you change the slip angles?

Tire loading directly impacts slip angles and in a very interesting way. On a single axle, two equally loaded tires will run at smaller slip angles than two unequally loaded tires. Increasing the weight transfer on the rear axle increases the slip angles and tends to make the car looser in the middle of the turn. Likewise, reducing the weight transfer on the rear axle reduces the slip angles and tightens up the rear of the race car.

Items such as spring rates, spring locations, Panhard bar (or J bar), 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, have a large impact on the amount of weight that transfers from the inside tire to the outside tire. Again, 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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