Jeff Lacina
December 1, 2008
Photos By: Ron Blevins, V6john

14 - What's The Difference Between Radial And Bias-Ply Tires?
Bias-ply tires have their underlying plies laid at alternating angles of less than 90 degrees to the centerline of the tread. Radial tires are constructed so that the plies are laid at 90 degrees to the centerline of the tread. That's the technical difference. The reason radial tires are dominant today is that they help improve fuel efficiency and handling; they also tend to dissipate heat better than bias-ply tires. Chances are, most people reading this article have never driven a car on bias-ply tires (drag slicks not withstanding); trucks maybe, but today, no modern passenger cars come with bias-ply tires. If you ever get the crazy notion to try some bias-ply tires, it's hugely important to never mix radial and bias-ply tires; dangerously erratic handling may result.

15 - What Is Hydro-Planing And What Does It Have To Do With Tires?
Hydroplaning can occur when the vehicle drives through areas of standing water, especially at highway speeds. If the standing water cannot disipate from under the tire quickly enough, the tire will lift off the surface of the road, supported by only the water, and hydroplaning will result. Because the affected tire will have almost no traction, cars can easily go out of control when hydroplaning. Avoid hydroplaning by slowing down in foul conditions. With the advent of computer-aided tread designs, most of today's street tires have been designed to maximize their ability to pump the water out of the tread. Most of these designs feature deep grooves running in the same direction as the tread, giving the water an extra channel to escape from under the tire.

16 - How Do I Set Tire Pressures For Autocrossing Or Road Course Driving In The Rain?
For starters, increase your tire pressure 6-10 psi from what you would normally run in dry conditions. As we just discussed, hydroplaning occurs when a wedge of water develops between the tire and road surface. Increasing the pressure "rounds" the profile of the tire by decreasing the amount the tire deflects when loaded with the vehicle's weight and cornering forces. This makes for a slightly smaller contact patch, which will put more of the vehicle's weight on a smaller area. It also helps keep the tread grooves more open so they can channel the water out from under the tire.

17 - How To Use Tire Pressures To Fine Tune The Handling Of Your Vehicle.
When racing on D.O.T. approved tires, air pressure is a major component you can use to make minor tuning adjustments to the handling characeteristics of your car, especially in situations where actual suspension adjustments are limited. Here is a handy chart you autocrossers and road course drivers can add to your "going to the track" notebook.

Tires And High-Performance Handling
AdjustmentsDecrease UndersteerDecrease Oversteer
Front Tire PressureHigherLower
Rear Tire PressureLowerHigher
Front Tire SectionLargerSmaller
Rear Tire SectionSmallerLarger
Front Wheel CamberMore NegativeMore Positive
Rear Wheel CamberMore PositiveMore Negative
Front Wheel ToeToward Toe-OutToward Toe-In
Rear Wheel ToeToward Toe-InToward Toe-Out
Front Wheel CasterMore PositiveMore Negative
Front SpringsSoftenStiffen
Rear SpringsStiffenSoften
Front Anti-sway BarSoften (Thinner)Stiffen (Thicken)
Rear Anti-sway BarStiffen (Thicker)Soften (Thinner)
Weight DistributionMore RearwardMore Forward