Relaxation length
Encyclopedia
Relaxation length is a dynamic 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.
It is also described as the distance that a tire rolls before the lateral force builds up to 63% of its steady-state value.
It can be calculated as the ratio of cornering stiffness over the lateral stiffness where
cornering stiffness, another dynamic property, is the ratio of cornering force over slip angle, and
lateral stiffness, a static property, is the ratio of lateral force over lateral displacement.
has been found to be nearly zero.
.
Slip angle
In vehicle dynamics, slip angle or sideslip angle is the angle between a rolling wheel's actual direction of travel and the direction towards which it is pointing...
is introduced and when the cornering force
Cornering force
Cornering force or side force is the lateral force produced by a vehicle tire during cornering.Cornering force is generated by tire slip and is proportional to slip angle at low slip angles. The rate at which cornering force builds up is described by relaxation length...
reaches its steady-state value.
It is also described as the distance that a tire rolls before the lateral force builds up to 63% of its steady-state value.
It can be calculated as the ratio of cornering stiffness over the lateral stiffness where
cornering stiffness, another dynamic property, is the ratio of cornering force over slip angle, and
lateral stiffness, a static property, is the ratio of lateral force over lateral displacement.
Values
Relaxations lengths have been found to be between 0.12 and 0.45 meters, with higher values corresponding to higher velocities and heavier loads. Tests on motorcycle tires have found that the ratio of cornering stiffness over lateral stiffness produces values 20-25% higher than those calculated as 63% of the steady state-value. The relaxation length assotiated with camber thrustCamber thrust
Camber thrust and camber force are terms used to describe the force generated perpendicular to the direction of travel of a rolling tire due to its camber angle and finite contact patch...
has been found to be nearly zero.
Importance
A tire's relaxation length controls how much the tire will contribute to speed wobbleSpeed wobble
Wobble, shimmy, tank-slapper, speed wobble, and even death wobble are all words and phrases used to describe a quick oscillation of primarily just the steerable wheel of a vehicle. Initially, the rest of the vehicle remains mostly unaffected, until translated into a vehicle yaw oscillation of...
.