Tire and Handling

Contribution by Oliver Sanchez

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Handling Adjustments for Competition per Yokohama Tires

	Possible Adjustments and Modifications to Evaluate	To Reduce Understeer or Increase Oversteer	To Reduce Oversteer or Increase Understeer
Tires	Front Inflation Pressure Rear Inflation pressure Front section width Rear section width Front aspect ratio Rear aspect ratio Front tread depth Rear tread depth	Increase (2.5psi increments) Reduce (2.5psi increments) Increase section width Reduce section width Lower aspect ratio Install higher aspect ratio Reduce Increase	Reduce (2.5psi increments) Increase (2.5psi increments) Reduce section width Increase section width Install higher aspect ratio Lower aspect ratio Increase Reduce
Wheels	Front wheel width Rear wheel width Front wheel weight Rear wheel weight	Wider Narrower Lighter Heavier	Narrower Wider Heavier Lighter
Alignment Settings	Front wheel camber Rear wheel camber Front wheel caster Front wheel toe Rear wheel toe	More negative More positive More positive Toward toe-out Toward toe-out	More positive More negative More negative Toward toe-in Toward toe-in
Anti-Sway Bars	Front Rear	Soften Stiffen	Stiffen Soften
Spring Rates	Front Rear	Soften Stiffen	Stiffen Soften
Shock Absorbers	Front Rear	Soften Stiffen	Stiffen Soften
Suspension Bushings	Front Rear	Soften Stiffen	Stiffen Soften
Brake Proportioning	Front Rear	Reduce pressure Increase pressure	Increase pressure Reduce pressure
Weight Distribution	Front Rear	Reduce Increase	Increase Reduce
Aerodynamic Spoilers	Front Rear	Increase downforce Reduce downforce	Reduce downforce Increase downforce

 

Using Tire Temperatures to Tune Handling

Tire temperatures indicate how severely your tires are stressed, because the harder a portion of a tire is working, the hotter it will be. The ideal competition tire temperatures range from 165 degrees Fahrenheit to 195 degrees Fahrenheit. An evaluation of tire temperatures will indicate if the tire inflation pressures are correct, if the alignment settings are correct, how well the vehicles handling is balanced, and if appropriately sized tires are being used on the vehicle.

It is important that you always take tire temperatures as close to a corner as possible. Temperatures after a long straight do not indicate how well the car is handling. Temperatures taken at an autocross or in the pits of a race track are usually an average of straights and corners. This is why testing on a skid pad is helpful because the car is continuously cornering. A skid pad is any level pavement with a circle marked on it. On a skid pad you can measure lateral acceleration while your car travels at its highest cornering speeds. Time the laps and calculate maximum lateral acceleration in G’s with the following equation:

Lateral Acceleration = 1.22 x Circle Radius/Lap Time (squared)

The radius you use in the equation should be the approximate radius that the center of your car is traveling. Once the car has run a minimum of five consecutive laps, a tire pyrometer is used to take the tire’s relative tread temperatures. The tire pyrometer’s temperature element is a needle that is inserted just under the surface of the tire’s tread (but never past the tire’s plies or belts.) Immediately after the vehicle stops, go to the front tire that was on the outside of the car on the skid pad or last turn. Insert the pyrometer’s needle into the outer should of the tire’s tread, wait a few seconds until the pyrometer’s reading stabilizes, note the tread’s temperature, then move to the center of the tire’s tread, repeating the process. Then quickly move to the rear tire on the same side of the car. You only have about one minute before the tire’s temperatures cools.

How to Interpret Tire Temperatures

If you are taking tire temperatures after consecutive laps on a skid pad or immediately following a long corner, the tire pyrometer readings will give you a very accurate picture of the vehicle’s performance. Correct camber is indicated when the two edges of the tread have the same temperature. Correct tire pressure is indicated when the temperature at the center of the tread is equal to the average of the shoulders’ temperatures. If the front tires are hotter than the rear, transfer more of the car’s cornering load to the rear. If the temperature of all the tires exceed 220 degrees Fahrenheit, Larger tires should be used.

Sample Interpretation of Tire Temperatures

Inside	Middle	Outside	Camber	Pressure
105	145	215	Too Positive	Too Low
165	195	185	Too Positive	Too High
190	190	190	Optimum	Optimum
180	200	180	Optimum	Too High
195	190	185	Too Negative	Appropriate

*Note: All temperatures indicated are in degrees Fahrenheit.

You should familiarize yourself with your tire warranty and all the information molded on the tire sidewall. The sidewall give the tire’s size, load range, maximum load and corresponding inflation along with other information, including the locations of tread wear indicators.