Know Your Knobbies

Tip #254 from the pages of The Total Motorcycling Manual

total motorcycling manual, dirtbike

Streetbike tires rely on rubber coming in contact with the road to generate grip. A dirt bike's tires depend on aggressive knobs and tread blocks to dig into the dirt surface. The height, hardness, and spacing of these knobs or tread blocks determines how a tire will perform.

Big adventure bikes or dual-sports ridden primarily on the pavement benefit from hard rubber compounds and large tread blocks spaced closely. This design increases tire life and grip on the street, but the tires’ performance in the dirt will suffer. Hard-compound knobbies work better in the dirt, but their street performance—especially under hard braking—suffers dramatically, and they wear out faster too. Soft, open-pattern knobs are the choice for soft soil and mud, but they are a terrible choice for the street.

Most tire manufacturers rate their dual-sport tires by percentage of street/dirt use. For example, a tire like the venerable Dunlop 606 is really 80/20 dirt/street, while a skin like that same company’s TR91 Trailmax is just the opposite, designed to be used on the street 80 percent of the time, and only 20 percent on the dirt.