Here's another version of...
Here's another version of the same-style rear tire. This tire is prepared for conditions in which gaining side bite is not as much of a concern or the track is very rough and tire wear must be minimized. The same groove pattern is here, but the sipes have only been cut across the tread of the tire (not around the circumference) to maximize forward bite. When siping a tire, Wright says it is important to keep the cuts as parallel as possible.
"You don't want to groove or sipe a tire deeper than the tread depth," Wright adds, "but track conditions can also affect your depth. If the track is hard and wears tires out quickly, you do not want to cut your grooves or sipes as deep. This will help keep your tires from chunking, which is when the track tears out chunks of rubber from the treads."
Wright also points out that the direction you groove or sipe depends on the corner of the car on which the tire will be mounted. For example, cutting sipes along the circumference of a rear tire will offer no performance advantage for acceleration. Sipes and grooves on the rear tires should be cut across the tire so that they are perpendicular to the rotation of the tire. That way, the grooves will help forward bite and braking. If he feels that gaining side bite will be important, Wright will sometimes add circumferential sipes to the right-rear tire.
On the front tires, the needs are different. Getting the car to turn is more important, so the priority when grooving and siping should be circumferential cuts. These will help the tire "dig in" when the driver turns the steering wheel.
When grooving and siping, you should always be careful about the density (or spacing) of your cuts. Too many cuts will weaken the tread and make a tire-especially the rears-more likely to chunk. Running a tire that's too soft on a high-grip track will make a tire more likely to chunk. Cutting too many sipes through the tread pattern will do the same thing. Hard edges, while they aid traction, also increase the probability of chunking. Chunking is costly in terms of traction, so it should be avoided at all costs.
Here is a mild example of...
Here is a mild example of chunking, which is the term used to describe a rough track ripping chunks of rubber out of a tire's tread. Wright says if chunking becomes a problem at a track, try widening the space between your sipes.
Sipes can be as close as 31/416 inch apart, but that distance must sometimes vary with different track surfaces and rubber compounds. It is important to make sure your sipe lines are as parallel as possible in order for you to make as many cuts as possible without getting sections too close together. Siping is a time-consuming and labor-intensive task, so you may want to consider special siping tools that can save you time and effort by making several cuts at once. One we've tried is Speedway Motors' Mega Siper, which can make as many as 14 cuts at once. The siper uses standard razor blades that are inexpensive and easily replaced so that it always makes easy cuts. Blades can be added or removed as necessary to set the spacing you want between cuts. Plus, since the siper keeps the blades aligned, you know that cuts made on the same pass will always be parallel.
Grinding is significantly different from grooving or siping but no less important. Instead of changing the shape of the tire tread, grinding prepares the surface of the tread. This knocks off the "new" surface from a fresh set of tires to get to the good rubber, and also removes the outside work-hardened layer of rubber from a used tire.
Another useful purpose for grinding is to round off sharp groove edges to reduce the possibility of chunking. Wright does this by holding the grinder at a slight angle and moving it across the tire in the same direction the tire will be acted upon by the track. For example, for right-side tires, Wright grinds from the outside of the tire to the inside. The opposite is true on a tire mounted on the left side of the car. Since the car is always turning left, forces are acting on the interior sidewall and trying to push out. Because of this, Wright grinds 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 well.