Cantidad de maltas

-As we now know, tires are the only vehicle component contacting with the road surface.

Friction between tires and the road surface creates acceleration, braking (deceleration), and cornering. Most of you learned in high school physics that: Ff = Cf * Fn

Where Ff is the friction, Cf is the coefficient of friction, and Fn is the normal force. Well, this equation only applies to very special cases where both surfaces are very hard and have reasonably smooth finishes. This equation certainly does not apply for tires.

-Tires’ frictional property cannot be expressed as an equation really well. If you use the above equation, Cf will decrease with increase in Fn. As normal force increases, coefficient of friction decreases. As a result, friction force does not increase as much as normal force increases.

-Q: What tire pressure should I run?

A: Unfortunately, the answer is different for every car due to suspension, driving style and tire differences. The best tool for determining ideal tire pressure is the pyrometer. A pyrometer measures tire temperature. It's also a great tool for evaluating alignment settings, tire sizes and sway bar settings. Would you benefit from more negative camber? Are your tires too small? Too big? A pyrometer can tell you.

-Tires get hot when they are loaded; acceleration, braking, cornering and steady state driving all deform tires and cause them to heat up. Tire temperature can tell much about how the load is carried and distributed over the tires.

-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 table below suggests tire inflation pressures for competitive driving. Tires should be reset to normal inflation pressures when returned to the street. These recommendations should be used as a starting point. Pressure can be adjusted to match the driver's preferences. Adjust pressure in 2 psi increments.

Type of Vehicle Position Pressure

Front Wheel Drive Front

Temperature readings should be taken when tires are fully warmed up, typically after 5 to 10 hot laps on the track. Readings should be taken immediately after the last hot lap, no cool down allowed.

-Measurements are taken with a tire pyrometer. The best type of pyrometer has a probe that is inserted into the tire tread. By measuring temperature below the tread surface, the probe provides improved readings since the tread surface cools relatively rapidly. Three readings are taken on each tire; inner tread, center tread and outer tread. Inner and out readings are taken 1 inch from tread shoulder and in the center of a tread block. Write down the readings for evaluation.

-Evaluating the readings

We can draw useful conclusions by evaluating each tire individually and by comparing readings of the tires. Tires have an ideal temperature range in which they produce maximum grip. When cooler than that range, tires loose grip. When hotter than that range the tires become "greasy", even hotter and they begin to break apart. Check with your tire manufacturer to find the

recommended operating temperature for your tires. A typical operating range for a DOT-R tire is 180F to 200F. Street tires tend to run a bit cooler and racing tires a bit hotter.

-Use the following table as a general guideline to evaluate readings:

Symptom Diagnosis

Center hotter than edges Tire pressure too high. Reduce 1psi for each 5degF delta.

Edges hotter than center Tire pressure too low. Add 1psi for each 5degF delta.

Inner edge hotter than outer Too much negative camber.

Out edge hotter than inner Not enough negative camber or too much toe-in.

Tire below ideal temperature range

Tire pressure too high, tire too wide, or springs/sway bars too stiff at that axle.

Tire above ideal temperature range

Tire pressure too low, tire too narrow, or springs/sway bars too soft at that axle.

Front tires hotter than rear

Car is under steering (pushing). Too much front

spring/sway bar, not enough rear spring/sway bar, front pressure too low, rear pressure too high, front tires too narrow, rear tires too wide.

Rear tires hotter than front

Car is over steering (loose). Too much rear spring/sway bar, not enough front spring/sway bar, rear pressure too low, front pressure too high, rear tires too narrow, front tires too wide.

-The chart below shows some of the changes you can make to change the balance of the car.

Guide To High Performance Handling

Adjustments Decrease Understeer Decrease Oversteer

Front Tire Pressure Higher Lower

Rear Tire Pressure Lower Higher

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. The Hoosier Radials can wear unevenly if underflated and seem to work best at much higher pressures, such as the mid 30s to as high as 50 psi. Underinflation 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. Avoid sliding the tires, locking up the wheels under braking and drive as smooth as possible.

-Note that some symptoms have multiple diagnosis; one or more may apply. Sometimes multiple symptoms appear simultaneously. Making one change at a time is advisable to best evaluate the impact of the change.

-It is wise to take and evaluate temperature readings frequently. Different tracks, changes in ambient and track temperature, tire wear, fuel level and more all affect ideal settings.

Adjustment in pursuit of peak performance is a non-ending task.

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.

Competition Tire Heat Cycling Service

-Many tire manufacturers use very aggressive tread compounds for the Track & Competition DOT-legal tires they’ve developed for autocrossing, track days and road racing. And just like other high performance parts, these tires will provide more consistent performance and last longer if they are properly broken in.

-The first time Track & Competition DOT tires go into service is very important. All tires deflect under load and their tread rubber compounds repeatedly stretch and relax as they roll into and out of contact with the road. This stretching breaks some of the weaker bonds between the tread rubber molecules, generating heat. If new Track & Competition DOT tires are initially run too aggressively, too hot or too long, some of the stronger bonds will also be broken which reduces tire grip and wear.

-Putting new Track & Competition DOT tires through an easy initial heat cycle and then not running them for a minimum of 24 hours allows the rubber bonds to relink in a more uniform manner than they were originally manufactured. Heat cycling actually makes Track &

Competition DOT tread compounds more consistent in strength and more resistant to losing their strength the next time they are used.

-While it’s important to heat cycle tires, how it’s done isn’t as important.

On the Track

-Heat cycling can be done by installing tires on the car and running 10 to 15 minutes on a

racetrack. Start with easy laps, and build up speed as the session continues. End up running 5-10 seconds off your normal pace and be careful not to spike the tire temperatures by spinning, sliding or locking the tires.

-An important step in tire heat cycling is that after being brought up to temperature, the tires require a minimum of 24 hours to relax and relink the bonds between the rubber molecules.

Drivers attempting to heat cycle tires in the morning for use a few hours later in the afternoon will not experience any benefits from the morning attempt at heat cycling. Heat cycling tires on Saturday means not using them again until the same time on Sunday.

By TireRack

TireRack’s heat cycling service begins by mounting the tire on an

appropriate-width wheel and inflating it to the desired pressure. It is then placed in our heat cycling machine which has three rollers positioned at the corners of a triangle. The tread flexes where it comes into contact with each of the rollers, stretching the rubber compound enough to progressively bring it up to temperature all the way around the tire and across the tread.

There is no artificial heat added by an oven, forced air or heat lamp.

The tread temperature is monitored with a pyrometer to confirm when the tire has reached the desired 170-180° F temperature. The tire is then

dismounted and stamped as Tire Rack heat cycled. Since the minimum 24-hour waiting period typically occurs while the tires are in transit, the tires are ready to use when they arrive!

The only thing our heat cycling service doesn’t do is scuff in the tires. The cost of heat cycling is

$15 per tire and is recommended by competition tire manufacturers.

If you have any other questions regarding tires, or any other topic, please don’t hesitate to contact us at [email protected].

For other technical information, please visit us at www.matrixintegrated.cc/technical.php.

(Special thanks to TireRack, SAE, Yoshiki "Yogi" Mogi at TAMU, Bill Hawe, TechGuys, and carcare.org for information.)