The laser straight sipes from...
The laser straight sipes from Speedway's Mega Siper can be seen in our test pass on an old tire. Photo by Rob Fisher
To do it right for front tires, hold your grinder at a slight angle and grind from the outside of the tire to the inside. For the left sides, do the exact opposite. Since circle track cars are always turning left (we hope) forces are acting on the interior sidewall and trying to push out. Because of this you should also grind outward from the inside edge of the tire. This helps to slightly round off the leading edge of the grooves so that they are less likely to be ripped off under side loading when the car is hooked up.
In a past article on the subject, CT found that many tire specialists prefer different tools for grinding. However, a popular option is a power sander with a variable speed control and replaceable pads; use a slower speed for softer tires and faster speed for harder tires. Use pads between #36 and #40 grit.
Anytime you groove or sipe your tires you need to pay close attention to the depth and spacing of your cuts. Why? Simply put, if you don't do it right you could cause your tires to chunk. Chunking is when small pieces of tire get ripped off of the tread. It's costly, because a chunked tire is a junk tire.
Apart from running a tire that's too soft on a high-grip track, here are a few items that will cause a tire to chunk:
* Too many grooves that weaken the tread blocks, reduce contact patch surface area and make the tire run hotter
* Cutting too many sipes through the tread pattern
* Leaving hard edges
You can notice three chunks...
You can notice three chunks in this tire. This is a mild example caused when the rough track tore pieces of rubber out of the tires tread. If you experience this problem try widening the space between your sipes. Photo by Jeff Huneycutt
Solving those issues is fairly easy, grinding will round off sharp groove edges to reduce the possibility of chunking. In addition, grinding your rear tires twice will help prevent chunks. Grind once laterally (across the tire) to prevent the tread from chunking under sideloading. A second grinding around the circumference of the tire will smooth out the leading edge of the treads so that they won't chunk under acceleration.
Grooves and sipes should always be cut perpendicular to the direction of the stresses applied to the tread. For example, rear tires are subjected to acceleration and braking forces circumferentially. Consequently, those grooves need to be cut across the tire thereby delivering bite in a front to rear direction. However, just because rear tires do not turn as front tires do, doesn't mean that lateral traction isn't important. By cutting grooves and sipes circumferentially around the tire you can increase the lateral traction of the rear tires as you negotiate the corners.
Front tires experience a different set of stresses than the rear tires because you turn your front tires to steer the car. Therefore, grooves and sipes must be cut at an angle in order for them to lay perpendicular to the direction of the tire stresses. Start by holding the tire between your knees and imagining a clock. 6 o'clock would be closest to your body while 12 o'clock would be the farthest away with 9 o'clock to your left and 3 o'clock to your right. You make all of your cuts in a pattern running from 8 o'clock to 2 o'clock. This is important to get right because if you cut the grooves the wrong direction you will reduce the braking force of the front tires and cause the car to push when entering the turn.
Grooving, siping, and grinding on tire is all well and good, but keeping detailed records as part of a tire management program is critical to maximizing your results. Prepping dirt tires is a time consuming task. As such, you want to make sure that you have all the proverbial ducks in a row before you hit the track. So as a little bonus to you, our valued readers, if you head over to www.circletrack.com you can download our very own CIRCLE TRACK Tire Record Sheet that you can print and take to the track.
Prepping a tire for dirt racing is an arduous task that is time consuming and labor intensive. But with the right tools and the right approach you can maximize your performance on the track. And that's what it is all about. If you follow our guidelines in this article and pay very close attention to the track conditions you will be in good shape.