# Slip angle

The gray area represents the contact area of ​​a tire (from above); the yellow dashed line is the intersection of the wheel center plane and the road plane; is the wheel contact point; indicates the speed vector of the wheel contact point and is the slip angle${\ displaystyle M}$${\ displaystyle v}$${\ displaystyle \ alpha}$

The slip angle for tires is the angle between the speed vector at the wheel contact point and the line of intersection between the wheel center plane and the road surface.

The wheel contact point is the intersection of three levels: the wheel center plane, the road surface and a plane that is perpendicular to the other two and goes through the wheel center.

A tire pointing straight ahead while the vehicle is moving smoothly straight ahead has a slip angle of 0 °, as does a stationary tire; a tire that points, for example, 5 ° to the left while the vehicle continues to move in a straight line because of a left turn due to understeer , has a slip angle of 5 °.

In order for a tire to be able to build cornering forces, the tread particles in the tire contact patch must be tense. In the case of a freely rolling wheel, this tension initially builds up in a triangular shape under the slip angle. In the rear area of ​​the wheel contact area, the deformation is partially reduced by sliding processes. As a result of this asymmetrical distribution of lateral forces, there is a tire return torque about the vertical axis. This tries to reduce the wheel lock. The larger the sliding area in the rear part of the contact area, the more the tire return torque decreases. In the case of large slip angles, it can even assume negative values ​​and accordingly acts in such a way that it can increase the wheel lock.

Bracing of the profile particles in the laces under an oblique run

## values

On a dry road, a car tire reaches its maximum cornering force at a slip angle of around 8–12 °, depending on the make and type of tire (summer or winter tires), after which it decreases again. The steering wheel announces the entry into this limit area , as the steering forces decrease. On motorcycles, the maximum cornering force on the rear wheel is around 4 ° of slip angle, and less on the front wheel.

Especially with sports and racing tires , the limit area begins at relatively small slip angles and is also quite narrow: the tire suddenly loses its grip. Formula 1 tires have their maximum cornering force at 5 ° ( slick ) and 6 ° for grooved tires, other racing tires have a slip angle of less than 8 °.

## literature

• Hoting, Ersoy, Gies: Chassis Manual Basics · Driving Dynamics · Components · Systems · Mechatronics · Perspectives. Springer Verlag, Berlin 2013, ISBN 978-3-658-01992-1 .

## Individual evidence

1. Michael Trzesniowski: racing car technology. 2nd Edition. Vieweg and Teubner Verlag, Wiesbaden 2010, ISBN 978-3-8348-0857-8 , p. 225.
2. ^ Friction potentials of modern motorcycle tires : reports of the Federal Highway Research Institute. In: Vehicle technology. Booklet F 9, Bergisch Gladbach 1994, p. 28 ff.
3. Michael Trzesniowski: racing car technology. 2nd Edition. Vieweg and Teubner Verlag, Wiesbaden 2010, ISBN 978-3-8348-0857-8 , p. 215.
4. ^ Giorgio Piola: Formula 1 technical analysis 2009–2010. Giorgio Nada Editione, Vimodrone (Milan), ISBN 978-88-7911-508-7 , p. 23.