Now that we’ve covered the “when” let’s take a look at the “how.” We’ll start with grooving. The art, and we do mean art, of using a heated iron to cut either U-shaped or V-shaped grooves in the surface of the tire. The goal is to get the grooves placed on the tire at the correct angle that will facilitate as much grip as possible. The problem is that grooving can only go so far. You still need a tire surface to meet with the track. Too many grooves and you reduce the surface area of the tire and your grip suffers. That’s where analyzing how many grooves you need comes into play.
Understanding that all of the factory pattern grooves are 8/32-inch or 1/4-inch deep is important for two reasons. Number 1: Additional grooves you cut should be the same depth as the factory grooves. Otherwise, as the tire wears your grooves will disappear before the factory’s rendering the tire useless. Number 2: If you cut grooves deeper than 9/32-inch you risk cutting in too deep, weakening the tire and eventually causing a blowout.
Here’s a helpful tip on grooving from Mr. Furney. “For anything under 35 laps, the grooving iron should be adjusted to cut a U-shaped groove with the bottom of the groove no more that 1/4-inch deep or the same as the factory tread groove. For longer features of 50 laps or more, tire wear may be significant. In those cases we need to consider the condition of the track at the end of the race. Often you start tacky and end dry slick. At the green flag you need a lot more grooving than you do at the end of the race. Therefore, for a long race you need to cut a V-groove as opposed to a U-groove. As the surface of the tread wears through the race, the percentage of your grooving will decrease thereby giving you an appropriately prepped tire for a dry-slick track.
For this article we’re using the patented Van Alstine G-1000 Tire Groover which we sourced through Speedway Motors. This groover has an instant-on feature so that when you touch the Teflon padded head to the tire surface the blade gets hot instantly. After smoking the tires with the highest setting we backed down to a “3” to groove our Hoosier D21s. This groover made quick work of prepping six tires for an upcoming trip to a central Florida high banked half-miler that usually goes somewhere between black slick and dry slick by nights end. The Late Model feature is run second, so the track should still have some tackiness by the time we get on. The 25-lap feature is not long enough for the V-grooves so we stuck with U-shaped ones and added some sipes.
Speaking of tire siping, did you know that it actually has its origin in the nautical industry? It was discovered that shoes with fine cuts in the soles at right angles to the direction of travel would assist sailors in maintaining a good grip on a wet deck in high seas. While the same principle works for race tires, siping also allows the tires to heat up faster by reducing the stiffness of the tread blocks. This is particularly beneficial on dry-hard/black slick or dry-slick tracks where there tends to be a lot of cautions as the tires will come back up to temperature quicker.
A tire under static load will deflect to a certain degree. A tire under a dynamic lateral load (as in going through a corner) will deflect even more. Siping a tread block increases the deflection and in turn generates more heat, consequently softening the rubber even more, thereby creating greater traction.