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Tire Care, Pressures, Service, Tubes, Useful Formulas, Mounting,
Radial Tires, Warranty

There are a number of guidelines to be followed in determining the correct size for your car, including the rules of the club that you might be racing with, the diameter and width of the rims you will use, the weight and power of the car, the clearance available under the fenders, the strength of the suspension and the stiffness of the chassis. Please call for recommendations.

TIRE CARE Race tires should be not be stored in high temperatures, in direct sunlight or in areas near welding equipment or electric motors producing ozone. A controlled atmosphere is ideal. New racing tires should be broken in ("scrubbed in") before using them "in anger". Tires should be gradually brought up to operating temperature without hard acceleration, braking or cornering, and then allowed to cool and cure before racing on them. This will help increase the life of the tire and reduce the possibility of blistering. PRESSURES Tires should have sufficient pressure so that the tire does not distort and roll under while cornering, and enough pressure to avoid the tire turning on the rim under braking or hard acceleration. Personal preference adjustment is then necessary. A tire pyrometer is most helpful. Our recommendations for Dunlop Formula Ford tires on a Formula Ford would be to start at 12/14 psi cold (front/rear) in order that the tires build up to an ideal 16/18 psi when hot. Dunlop L series tires on an XK120, for example, might be set for 34 psi whereas a small production car might be in the 24/26 psi range. TUBES Modern racing tires are designed to be tubeless. If you have a wire wheel, you must use a tube and a rubber band over the wire ends. A tube must also be used if the wheel is not designed to be tubeless. Inner tubes with rubber valve stems are available in sizes to fit each tire. These are good quality and are $15 each. We also carry the heavy duty competition inner tube made with a brass valve stem and lock nut which locks the tube to the wheel. These inner tubes are handmade by Classico in England, and are available in many sizes for $60 each. They are recommended when originality is important, or where there is a risk that the wheel might spin on the rim under hard acceleration. Rim bands are available at $5. USEFUL FORMULAS: Car MPH = Engine RPM x Tire OD x 0.002975 / Gear Ratio x Ring-pinion Ratio Revs Per Mile = 20168/tire diameter (inches) MOUNTING Always have your tires fitted by a competent service tire expert who understands the special requirements of competition tire fitting. Fitting should always be carried out with extreme care to avoid damage to the bead area of the tire which is of critical importance in tubeless tires. Wheels should always be carefully checked for hidden cracks, rust patches and chips which will prevent a good air seal. Tires should not be inflated to over 40 psi.

RADIAL TIRES Many vintage production sports cars are racing on street radials. These are DOT approved, are relatively inexpensive and are readily available. Street radials, however, give the driver less feedback about the limit of adhesion of the car than do bias ply racing tires. The traditional Dunlop and Goodyear racing tires are bias ply constructed and are easier to drive on the limit than a radial tire. Those of us that race only a few times a year need all the help we can get, and bias ply racing tires are a big help. The graph below helps explain the difference in characteristics between the tires. As you can see, the side force generated by the radial tire increases with increasing slip angle on the tire However, with increasing side force, after the maximum side force has been reached, the radial tire's side force drops off. This is the characteristic of the radial tire, and is apparent to the racing driver by a sudden loss of traction at the limit of adhesion. The bias ply will also develop its side force as the slip angle increases, but at a slightly lesser slope. The peak of the bias ply curve may be the same as that of the radial tire, but the slip angle will be greater. However, at the limit the bias ply does not have a real peak, but rather a plateau. Increasing slip angles do not cause a sudden drop off of the side force, but usually the side force is maintained at quite large slip angles. Therefore the driver with bias ply tires has a much larger range of slip angles to feel what the car is doing. The result is usually a driver who will go faster and who will have more fun. WARRANTY Racing tires are specially designed and compounded for competition use only. No warranty is given to racing tires (including any warranties as to merchantability or fitness), either expressed or implied, with respect to Dunlop and Goodyear racing tires and tubes. They are not suitable for everyday road use, and it may be illegal to do so.