Slip (vehicle dynamics)
Encyclopedia
In vehicle dynamics
, slip is the relative motion between a tire
and the road
surface it is moving on. This slip can be generated either by the tire
's rotational speed being greater or less than the free-rolling speed (usually described as percent slip), or by the tire
's plane of rotation
being at an angle to its direction of motion (referred to as slip angle
).
In rail vehicle dynamics, this overall slip of the wheel relative to the rail is called creepage. It is distinguished from the local sliding velocity of surface particles of wheel and rail, which is called micro-slip.
The slip is generally given as a percentage of the difference between the surface speed of the wheel compared to the speed between axis and road surface, as:
where
is rotational speed of the wheel, 
is wheel radius and 
is vehicle speed. Meaning a positive slip means the wheels are spinning and negative that they are skidding. Locked brakes, 
, means that 
is -100% and spinning on the spot, 
and 
≠ 
, means that 
∞.
Vehicle dynamics
Vehicle dynamics refers to the dynamics of vehicles, here assumed to be ground vehicles. Vehicle dynamics is a part of engineering primarily based on classical mechanics but it may also involve chemistry, solid state physics, electrical engineering, communications, psychology, control theory,...
, slip is the relative motion between a tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
and the road
Road
A road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...
surface it is moving on. This slip can be generated either by the tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
's rotational speed being greater or less than the free-rolling speed (usually described as percent slip), or by the tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
's plane of rotation
Plane of rotation
In geometry, a plane of rotation is an abstract object used to describe or visualise rotations in space. In three dimensions it is an alternative to the axis of rotation, but unlike the axis of rotation it can be used in other dimensions, such as two, four or more dimensions.Mathematically such...
being at an angle to its direction of motion (referred to as slip angle
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...
).
In rail vehicle dynamics, this overall slip of the wheel relative to the rail is called creepage. It is distinguished from the local sliding velocity of surface particles of wheel and rail, which is called micro-slip.
The slip is generally given as a percentage of the difference between the surface speed of the wheel compared to the speed between axis and road surface, as:
where
is rotational speed of the wheel, is wheel radius and is vehicle speed. Meaning a positive slip means the wheels are spinning and negative that they are skidding. Locked brakes, , means that is -100% and spinning on the spot, and ≠ , means that ∞.