Relaxation length is a property of pneumatic tires that describes the delay between when a slip angle is introduced and when the cornering force reaches its steady-state value.[1] It is also described as the distance that a tire rolls before the lateral force builds up to 63% of its steady-state value.[2] It can be calculated as the ratio of cornering stiffness over the lateral stiffness, where cornering stiffness is the ratio of cornering force over slip angle, and lateral stiffness is the ratio of lateral force over lateral displacement.[1]
The relaxation length ... is an important parameter that controls the lag of the response of the side force to the input slip angle.
The relaxation length represents the distance the wheel has to cover in order for the lateral force to reach 63% of the steady state force.