INDIANA, Pa.—When you get right down into the dirt—or other racing surfaces, for that matter—what's it take to get a tire ready to race?
It requires a lot more than just rolling those round, black babies off the truck and bolting them onto a race car, then hoping they'll hold up and your chosen driver gets to bask in the glory of the checkered flag.
Specialty Tires of America Inc.'s (STA) Race Tires America division has been a staple of the Indiana-based tire maker for at least half of its more than a century in business, from when Harry McCreary founded the company in 1915 as McCreary Tire & Rubber Co. Today, STA derives about 20 percent of its annual revenue from racing products like its America Racer-brand tires used in a variety of applications such as late model, modified, sprint and street stock car tires used both for dirt and asphalt racing, according to the company.
The following is a nuts-and-bolts look at racing tire prep information from Race Tires America's website. Frankly, tire preparation could be a website all on its own, since STA said different tires and different track surfaces usually result in different tire preparations.
Asphalt racing tire prep:
This track surface requires a special scuff procedure. As with any bias-ply racing tire, it's a good idea to scuff (breakin) new tires before use in competition—asphalt racing compounds need a light heat cycle to condition, or toughen, the tire for max-imum performance and longevity, STA said.
Often it is not possible to scuff a tire before racing, but if possible, these steps should be followed: Run six to eight laps at no greater than three-quarter 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 proved 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, STA advises. 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, just 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.
Grooving—The purpose of grooving a tire is to remove rubber and allow it to run cooler, and to possibly enhance grip. Grooving does two things: It creates sharp edges for grip and more resistance against the car sliding or spinning the tires. It's also 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. This can be achieved 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 the race car. Again, grooving helps reduce heat in the tire—allowing heat to escape from the block or the rib of the tire as the air flows across the tread.
Siping—Unlike grooving, which helps cool a tire, siping will build heat in a tire. In a nutshell, sipes are razor-blade 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 allows the tire to heat up more quickly 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—and that will cause a loss of traction or tire failure.
STA notes on its race tires website that, while grooving and siping can help the performance of a tire, altering it actually will increase the tire's wear rate. Too many cuts can compromise the tread and damage the tire.
There is always a trade-off when cutting a tire, the company said, advising that “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, STA said 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” and not give up like a softer compound tire.
“Again, each scenario is different depending on track conditions,” STA added.