Racing Tires - Sipes & Grooves

Tire siping is the same principle as grooving but at a smaller level and with different desired results. Siping involves using a razor blade to cut at different depths depending on the track conditions. Sipes are not as prominent as grooves, but sipes can drastically change how the car is handling. The goal is to allow the tire to heat up quicker and then maintain that heat by allowing the tire to cool easier. Siping is beneficial because it allows you to cut grooves into the tire, but it doesn't actually take anything away from the rubber because all you're cutting is a line the size of a razor blade.

When the track is in great shape, you will need to focus on more than just grooving. In fact, some teams do away with grooving altogether and focus completely on siping. Because again, grooves are meant to be used when there isn't much traction or when the track is really rough.

Without sipes or grooves in tires, racers run the risk of overheating and blistering the tires. They will not have the traction that they should and the car will be a handful to drive. It's important to remember the optimum operating temperature for the tire of choice. Remember, too, the softer the tire, the lower the operating temperature; and of course, the harder the tire, the higher the optimum operating temperature, so you will need to address your air pressure accordingly.

The depth of the grooves or sipes is another factor to consider. As a rule of thumb you should never groove the tire deeper than the tread depth. If you cut it too deep, the tire will actually come apart as you are racing. This is called chunking, which occurs when the track gets rough and the grooves are too deep in the tire, and a chunk of rubber rips from the tire. Sipes are usually cut less than a quarter inch into the rubber.

Problems arise for dirt track owners and series promoters because of tires. They have all had to address the tire prep issue and now most tracks and series operate with a "sniffer," which can detect if any type of prep has been applied to the tire. The Lucas Oil Late Model Dirt Series does not allow any type of prep and only allows tires from Hoosier and American Racer. The MARS Dirtcar Series has the same requirements, except that series runs exclusively on Hoosier tires, allowing five compounds.

It is vital to keep a dirt track book. Every time you visit a track and see how the track dries out or comes apart, you should be writing down exactly what has happened. Then, if you don't win the race, go and look at the race winner's tires to see if you can tell what type he uses, or what angle of grooves he has cut into the tire. By taking this notebook to each race, you can improve each time you compete at a particular track. Don't rely on just your memory. The dirt track tire can be more complex than the asphalt tire because of the numbers of compounds out there and the changing track conditions. By taking notes and keeping a steady eye on the track, you can learn exactly what you need to do to your tires based on the track conditions.