Tire preparation could be a web site all on it’s own. Different tires and different track surfaces usually result in different tire preparations.
Asphalt Racing Tire Prep:
As with any bias ply racing tire, it is a good idea to scuff (break- in) new tires before use in competition. The reason is that asphalt racing compounds need a light heat cycle to condition, or toughen the tire for maximum performance and longevity.
Often it is not possible to scuff a tire before racing, but if possible, you should follow these steps. Run 6-8 laps at no greater than ¾ speed, then let the tire completely cool down. A second light scuff session followed by storing the tire several days or even a week is recommended, and has proven to be ideal for preparing a tire for competition. Scuffing brings the tire up to the lower end of its operating temperature, but not too hot. DO NOT DRIVE AT TOP SPEED DURING THE SCUFF SESSION. This will cause the tire to “give up” or “fall off” prematurely in competition.
Dirt Racing Tire Prep:
Altering tires by grooving and siping can maximize the amount of traction and enhance the performance of the tire. However, how to prepare a tire is dependent on many variables such as track conditions and how the track will change throughout the day. Obviously, a heavy track will behave far different than a black slick track. Therefore there is no one “proper” way to prepare a tire that will work in all conditions, however this will give you the basics on grooving and siping.
The purpose of grooving a tire is to remove rubber and allow it to run cooler, and to possibly enhance grip. Grooving a tire does two things; one is to create sharp edges for grip and more resistance against the car sliding or spinning the tires. The second is done to help sling dirt off the contact patch of the tire by helping the tire clean itself before it rotates back around and makes contact with the track. There are many different ways to groove a tire but just starting out with the basics can help tremendously. Rear tires transfer the torque to drive the car, so when grooving rear tires the grooves should be cut perpendicular to the rotation of the tire. This will promote forward bite and help the tire “dig” into the track. Grooving front tires will allow for more steer in the car, which will help the car turn with less resistance. You can achieve this by making grooves in the tire that run parallel to the direction of rotation. This helps the tire dig into the racetrack (side bite) as the driver turns their car. Again, grooving helps reduce heat in the tire. It allows heat to escape from the block or the rib of the tire as the air flows across the tread.
Unlike grooving, that helps cool the tire, siping is done to build heat in the tire. In a nutshell sipes are razor blades cuts, or tiny slits into the tread. As the tire rotates and makes contact with the track the inside of the sipes will rub against each other and generate friction and heat. The sipes will also allow the tread block or rib to flex more which also generates more heat. This will allow the tire to heat up quicker in fewer laps, causing the tire to “fire” or grip faster. Unlike grooving, siping a tire only puts a slit in the tire and doesn’t remove rubber. Caution must be used in siping or grooving since cutting the tread too deep can cause the blocks to rip or tear which will cause traction loss or tire failure.
While grooving and siping can help the performance of the tire, altering a tire will actually increase the wear rate of the tire. Too many cuts can compromise the tread and damage the tire. There is always a trade-off when cutting a tire. Each racer should calculate what they wish to accomplish. If getting the tire to “fire quickly” is the goal, then siping is an option. However, if the track is taking rubber and is black slick, the track will get very abrasive and the tire can overheat and cause it to give up and not repeat. If the goal is to be fast late in the run, then minimal siping may be the best option on softer compounds, since the tire will run cooler than the same tire with more siping. In this situation it may be better to use a harder compound and more siping to get the tire to heat up later in the run but won’t give up like a softer compound tire. Again, each scenario is different depending on track conditions.