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- Engine Tuning
The table below suggests tire inflation pressures for competitive driving. Tires should be reset to normal inflation pressures when returned to the street. These recommendations should be used as a starting point. Pressure can be adjusted to match the driver's preferences. Adjust pressure in 2 psi increments.
|Type of Vehicle||Position||Pressure|
|Front Wheel Drive||Front|
|Front Engine/Rear Drive||Front|
|Rear Engine/Rear Drive||Front|
When racing on DOT approved tires air pressure is a major consideration in tuning the handling of your car, especially in cases where suspension adjustments are limited. The chart below shows some of the changes you can make to change the balance of the car.
|Guide To High Performance Handling|
|Adjustments||Decrease Understeer||Decrease Oversteer|
|Front Tire Pressure||Higher||Lower|
|Rear Tire Pressure||Lower||Higher|
|Front Tire Section||Larger||Smaller|
|Rear Tire Section||Smaller||Larger|
|Front Wheel Camber||More Negative||More Positive|
|Rear Wheel Camber||More Positive||More Negative|
|Front Wheel Toe||Toward Toe-Out||Toward Toe-In|
|Rear Wheel Toe||Toward Toe-In||Toward Toe-Out|
|Front Wheel Caster||More Positive||More Negative|
|Front Anti-sway Bar||Soften (Thinner)||Stiffen (Thicken)|
|Rear Anti-sway Bar||Stiffen (Thicker)||Soften (Thinner)|
|Weight Distribution||More Rearward||More Forward|
To get even tire wear when using DOT tires you must be very careful not to use too low of a tire pressure. The Hoosier Radials can wear unevenly if underflated and seem to work best at much higher pressures, such as the mid 30s to as high as 50 psi. Underinflation will cause a thin ring of wear at the very edge of the tread. The best results on the Hoosiers seem to come when they are properly inflated, on fairly wide wheels, and with a good amount of negative camber. If properly inflated, these problems can be avoided. Probably the biggest adjustment you can make to improve tire wear is the driver. Avoid sliding the tires, locking up the wheels under braking and drive as smooth as possible.
TIRE PRESSURES IN THE RAIN
For both autocross and road racing, increase tire pressures 6-10 psi from what you would normally run in dry conditions. Hydroplaning occurs when a wedge of water develops between the tire and road surface. This wedge can actually lift the tire off the road and eliminate traction. Increasing the pressure rounds the profile of the tire by decreasing the deflection of the tire. This results in a smaller contact patch - narrower and shorter. It also helps keep the grooves in the tread open so they can channel the water out from under the tire.
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