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Dirt track race cars can be very difficult to set up. Depending on the condition of the track and your driving style, there can be two very different approaches to your chassis tuning.
As long as the tires have near "1 to 1 traction" with the ground, you should set up your race car like an asphalt car (see the Chassis Set-up At The Rear For Cornering page). However, if you have to apply opposite lock steering (turning the steering wheel to the right) and you drive the car throughout the corner balancing it with the throttle, then you should use the tuning tips on this page.
When the rear tires are sliding or spinning, the single largest factor affecting the bite (grip) is the load on each tire. In this condition the tire with the most weight (load) gets the most bite. Or you could think of this as the tire with the least weight gets the least amount of bite.
A standard transmission clutch is a good similarity to this truism. Try this test at home and you will see how this works. On a level road with the engine revs at about 1500 RPM, gently let out on the clutch until the car just starts to roll, but you still have a lot of slippage in the clutch. Now, without changing the clutch load, press the throttle to the floor. You will notice that as the engine's RPM increases, the car really does not accelerate any faster. However, if you change the clutch load, the car will accelerate very differently. This is exactly the same physics as the sliding (or spinning) rear tires. Or in other words, If the tires are spinning and you spin them faster the car seldom will go any faster.
So, if you have "backed it into the corner" and are driving through the turn with the throttle, then the loading on each rear tire will have a large effect on how the race car handles. Increasing the load on the right rear tire will tend to make this tire push forward harder and the back end will come on around as you apply the throttle. Increasing the load on the left rear tire will make that tire push forward harder and tighten up the rear end of the race car.
Items such as spring rates, spring locations, Panhard bar (or J bar), all affect the weight on the tires 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. Again, the simplest way to know how much weight is on each tire during a corner is with a computer program.
Keep in mind that these causes and effects are true as long as the tires are sliding. Remember, racing can be dangerous. Always use your best judgment and the best tools!
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