Competition Tyre Pressure
When racing on D.O.T. 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. Please note that the air pressure changes are different on the BFG Comp T/A R1 than most other tires due to the asymmetrical sidewall construction.
Guide To High Performance Handling
Adjustments - Decrease Understeer - Decrease Oversteer
Front Tire Pressure (All except BFG Comp T/A R1) - Higher - Lower
Rear Tire Pressure (All except BFG Comp T/A R1) - Lower - Higher
Adjustments - Decrease Understeer - Decrease Oversteer
Front Tire Pressure (BFG Comp T/A R1 Only) - Lower - Higher
Rear Tire Pressure (BFG Comp T/A R1 Only) - Higher - Lower
Adjustments - Decrease Understeer - Decrease Oversteer
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 Springs - Soften - Stiffen
Rear Springs - Stiffen - Soften
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 D.O.T. tires you must be very careful not to use too low of a tire pressure. Both the BFG Comp T/A R1 and the Hoosier Radials can wear unevenly if under inflated. The start point for the R1 should be close to the factory recommended pressures for your car, typically in the high 20's to mid 30's in psi. The Hoosier Radials seem to work best at much high pressures, such as the mid 30's to as high as 50 psi. If under inflated the R1's tend to wear near the first groove in from the outer shoulder, which has been termed the "Evil Groove O' Doom". On the Hoosier's, under inflation 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. Avoided 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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The Importance of Tire Temperatures
In the course of testing the handling of a car, use tire temperatures and driver feel to make adjustments. It is critical to monitor tire temperatures often. They offer valuable clues to the setup of the car. The areas of adjustment that tire temperatures are used for include: tire pressure, camber, body roll, shock settings, wheel width and transient handling response.
Troubleshooting Tire Temperatures
Reading - Handling problem - Reason
All tires too hot - - Compound too soft for track and ambient temperature conditions.
Front tires too hot - Understeer - Front tire pressures too low.
Rear tires too hot - Oversteer - Rear tire pressures too low.
Inside edges too hot - Too much body roll - Too much negative camber or too much toe out.
Outside edges too hot - Too much body roll - Too little negative camber, too little toe out or too much toe in or wheel width too narrow for tire width.
Center of tread too hot - - Tire pressure too high.
Edges on too hot - - Tire pressure too low.
All tires too cold - - Compound too hard for track and ambient temperature conditions or car not being driven to limit.
Front tires too cold - - Inadequate load on front tires.
Rear tires too cold - - Inadequate load on rear tires.
