A tire with an "aggressive" tread pattern, that is, one with knobs or bumps of various shapes, designed to dig into soft surfaces for better traction Knobby tires get better traction on soft surfaces such as mud, gravel, snow, and dirt, compared with smooth treaded tires Knobby tires perform extremely badly on paved surfaces The knobs greatly increase rolling resistance, and create annoying vibrations They also corner badly on pavement, due to squirm