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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.