Siping tools use a series of razor blades to cut slits into a tire. Properly siping a tire
"One trick some racers have discovered to make this a little easier," he continues, "is to make your uts with two different blades. The first time around they will groove their tires with a round-bottom blade, maybe a 1/8-inch blade. Then, after their tires have worn and they decide to regroove, they will come in with a No. 5 flat-bottom blade. Now, the No. 5 is a little bit wider, so you are straddling that groove to give you a fresh edge. And it's not really cutting any deeper because the first time around you were cutting with a round bottom, so the flat-bottom blade doesn't cut much deeper, but it does cut more on the sides of the groove to sharpen up the edges."
If you are planning from the beginning to get all the use out of a set of tires you can get, you can plan ahead when grooving your tires. Instead of completely cutting up a new set of tires, Schankel says you can leave room to cut in a new set of grooves later on. Then, when the tire becomes worn and begins losing traction, you can go back in and cut additional grooves.
By having fewer grooves than the competition, you will have to face the fact that you may be giving up some performance in the early life of the tire. But if your goal is to maximize your track time and not necessarily to win every race, this may not be a problem for you. Just make sure not to cut your grooves too close together or your tire might start "chunking" or tearing apart on the racetrack. Unfortunately, we cannot tell you exactly how close "too close" is because it varies greatly depending on the softness and composition of the tire, your car's power and setup, and even the track itself.
The greatest wear on the grooves in your tires will be from trying to accelerate the car. Braking will also wear the grooves, but not nearly as much. This means that with some tread patterns you can flip the tires around and use the back of the groove to provide a fresh edge. If you are running the same wheel offsets you can probably switch the left-side tires to the right and vice-versa. This may help you get an extra run out of a set of rear tires before having to regroove them.
Siping is the process of cutting slits in the tread of your race tires. Sipes serve several purposes, some of which help improve traction while others help improve tire durability. Siping is definitely a labor-intensive process, but it is quite helpful when allowed by the rules.
Most sipers depend on the sharpness of the razor blades to cut through the tires. But this
"Siping has a few advantages," Schankel says. "First, it gives you extra edges which helps traction, but the slits also make a hard tire act softer. The slits also help a tire heat up quicker so you reach optimum traction sooner. The heat builds up when the sides of the slits work against each other. But after the tires have heated up, those sipes will open up and allow the tires to cool down. They also keep the tire from getting too hot. A tire that gets too hot will glaze over, and you don't want that. So siping your race tires will not only help improve performance, but should also help a tire last.
"As a general rule, you usually only want to cut your sipes about 1/16-inch deep. If you sipe deeper than that you might see some of the rubber ripping out. But then again, conditions will change the best depth for cutting your sipes. Sometimes you may need them deeper, sometimes shallower." Try asking around at your racetrack to see what works best for other racers and then experimenting a little on your own.
Sanding Or Grinding
In many lower-level Dirt Late Model racing classes, the rulebook prohibits any kind of cutting on your tires. This includes both grooving and siping. If you are willing to bend the rules, it is conceivable that you could regroove a used set of tires to get a fresh edge, but the reality is that it is very hard to regroove a tire so perfectly that it wouldn't be noticeable.
Instead, if you are trying to make your tires last as long as possible and your rules prohibit cutting, you can break out the power sander. Using a light-grit sandpaper, use the sander to lightly go across the top of the tire to knock down the rolled edges off of your grooves. Make sure to sand the entire tire evenly so that you do not create an unbalanced condition or cut waves into your tire. Done correctly, your work should be hardly noticeable (even though few rulebooks specifically prohibit this since sanding is often necessary to knock the glaze off of a tire). Sand off just enough to restore the edges of your grooves, and you are good to go.