Engine and chassis guys often don't want to hear it, but in many ways the tire specialist is right when he says that those four black rubber doughnuts are the most important things on any race car. It's true because the tires are the only things connecting your race car to the track, and their ability to maintain traction when accelerating, braking, and turning determines how quickly you can make a lap. So finding ways to get better traction from your tires helps efficiently translate power into speed.
Many tracks, particularly those hosting Late Models and Super Stocks, still allow race teams to modify their tires to enhance traction. You can alter your tires chemically (by using a traction compound to soften the rubber) or physically. In this article, we will concentrate on the physical aspect of enhancing traction. Chemically altering racing tires is still done, but with so many compound choices available, many professional racers say that the old science of soaking tires is no longer a necessity.
Here's an unmodified Hoosier...
Here's an unmodified Hoosier tire for the right-front wheel. It already has a good tread design that provides lots of edges in both directions to increase traction on dirt racetracks, but it can be improved.
There are three major components when it comes to physically altering a dirt tire. They all, however, are designed to reshape the tire's surface or tread pattern. Grooving is the process of cutting new groups into the tread pattern. The depth and width of the grooves can vary depending upon the tool used and the desires of the tire specialist. Siping a tire is similar, except it involves the use of a narrow blade that only cuts a small slit in the rubber instead of a groove that leaves a channel in the tread pattern. Grinding is the third option, and it is the process of using a powered sander to remove the first few thousandths of an inch of rubber from a tire. Using all three processes, you can dial in a set of tires to the conditions of your racetrack.
The process of grooving and siping race tires is a lot like judging a beauty contest: Everybody generally agrees on what works best, but there are many different ideas about the finer details. We spoke with Lance Wright, tire specialist for Barry Wright Race Cars. Lance works with Barry Wright's house car, which is driven by Dennis "Rambo" Franklin, who is the 2006 Southern All-Stars Dirt Late Model touring series champion.
"Generally, the more edges you can put in a tire, the more grip it will have," Wright explains. "You want to add grooves to a tire when the track is muddy. You want the tire to sling the mud off before it spins all the way around and makes contact with the track again. Grooving the tire helps sling the mud off."
This is a Hoosier rear tire...
This is a Hoosier rear tire that Wright has modified. It differs in stock form from a front tire because the tread pattern is squared up. Wright cut two grooves 90 degrees from each other through each square tread and then bisected each of the four blocks in the tread with four sipes (two horizontal and two vertical). The extra edges created by the grooves and sipes not only increase traction, but also help the tire reach prime operating temperature more quickly.
Grooving requires a special tool that heats a U-shaped blade. The heat helps melt the tire rubber so that the blade makes a clean cut in the tire.
Siping is similar to grooving in that it is a process of cutting the tire, but a sipe is a slit that does not create an open channel in the tire rubber like a groove does. Sipes are normally cut with razor blades, and although they may not look like much, they can actually have a large influence on how the tire handles.
"Edges not only increase traction, they also help the tire heat up and cool down faster," Wright explains. "So siping a tire will help it heat up more quickly and reach a good operating temperature in fewer laps. This can help you get a jump on other cars on the racetrack if your tires are gripping better, sooner."When track conditions are ideal, Wright will spend more time siping than grooving. This is because siping adds edges to a tread without actually removing any rubber. With siping, you can put the same amount of rubber on the track while also adding edges. Because they are narrower, you can also run three or four sipes where you would only have enough room for one groove.