Whittle: With a little trial and error you
can make your own tread patterns.
THE BASICS OF TIRE GROOVING Dear MXA, I bought a tire groover, still in the box, at a garage sale, but I don’t know a thing about how to groove a motocross tire. Can you help me? A common misconception is that tire grooving is a way to get more motos out of a knobby, but in reality, grooving tires is actually a way to decrease the life of a tire. A grooved knob simulates the grip of a softer rubber compound without maintaining the overall stoutness of the knob. It increases the number of biting edges and improves knob rollback. By grooving an old tire, which has hardened, or a new tire that is too firm, a rider can fine-tune his sneakers for track conditions. But first he has to understand knob rollback. What is knob rollback? Under acceleration, the knobs of a tire are pushed backwards. Knobs flex more on the front side of the block than on the rear. This flexing puts more rubber in contact with the ground. On hardpack tracks, the size of this contact patch has just as much to do with traction as does the biting edge of the knob. Hardpack tires use a soft rubber compound. It’s important to remember this, because when you groove the top layer of the knob, it increases the amount of rollback (flex), making soft rubber compounds act even softer. We don’t know what brand of tire groover you bought or the kinds of blades that came with it, but the best blade for grooving a motocross tire is a 4–5mm-wide, U-shaped horseshoe blade with a consistent bottom radius. Start with cutting a groove through the center of the knob by going laterally across the width of the tire. The drive knobs (the ones that make constant contact with the ground) are best suited to a straight groove across their width. On the transition knobs, you should cut grooves at a 45-degree angle (so that they scoop). As a rule of thumb, stay away from cutting the side knobs. They have less support, so grooving a side knob typically makes it too flexy to be of any use. The Tread Doctor is a popular tire tool, but it is not a tire groover. Instead, it allows a backyard tire engineer to cut new edges on the faces of the knobs. This does give a worn tire a new lease on life, but if you cut too much of the knob face, the knobs will get flexier, especially when they heat up mid-moto, and start to wiggle. While a sharp edge is good, a spongier knob is not. It is also possible to use the Tread Doctor to remove a complete row of knobs. This is not a silly idea. At super-muddy races, where the ground is more like tapioca than dirt, there is some benefit to removing the first lean transition knobs. Opening up the tread pattern allows the tire to fling dirt out at lower tire speeds. In tight sections, the tire stays lighter and grabs better when the tread isn’t plugged up. To remove the lean knobs, it takes a combination of a box cutter, side cutters and a Tread Doctor tool. Remember when we said that grooving tires doesn’t make them last longer? Why not? With a grooving tool you create extra driving and braking edges, but you also take stiffness off the top edge of the knob. The knob flexes further, grabs more, slips less and builds more heat. Thus, it wears out quicker. After you groove your tires, always take the time to inspect the knobs before each ride, paying special attention to the bottom of the groove. That is where the failure will first occur.