Tyre load sensitivity

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Tire load sensitivity describes the behaviour of tires under load. Conventional pneumatic tires do not behave as classical friction theory would suggest. Friction theory says that the maximum horizontal force developed should be proportional to the vertical load on the tire. In practice, the maximum horizontal force Fy that can be generated is proportional, roughly, to the vertical load Fz raised to the power of somewhere between 0.7 and 0.9, typically.

Tires typically develop this maximum lateral force at a slip angle of 6-8 degrees, although this angle increases as the vertical load on the tire increases.

[edit] Example

As an example, here is data extracted from Milliken and Milliken's Race Car Vehicle Dynamics, figure 2.9:

Vertical load	Fy/Fz	Slip Angle
(lbf)	max	degrees
900	1.10	5.6
1350	1.08	6.0
1800	0.97	6.7

The same sensitivity is typically seen in the longitudinal forces, and combined lateral and longitudinal slip.