where Ω Ω is the longitudinal component of the rotational speed of the wheel, r is wheel radius at the point of contact and v x is vehicle speed in the plane of the tire. A positive slip indicates that the wheels are spinning; negative slip indicates that they are skidding. Locked brakes, r e Ω Ω = 0 , means that slip = − − 1 = − − 100 % % and sliding without rotating. Rotation with no velocity, r e Ω Ω ≠ ≠ 0 and v = 0 , means that slip = ∞ ∞ .