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Tyre grip

Tyre grip

Tyre grip

(OP)
The theoretical grip from an automotive tyre is simply R*mu, where mu is the co-efficient of friction of the tyre & R the reaction force between the tyre & ground.
Consequently the maximum cornering & braking accelerations of a car are simply mu*g (assuming no aerodynamic effects).
In that case, why do high performance cars have wide tyres? In theory the amount of grip available is independant of the area of the contact patch. Discussions with tyre engineers & race-car builders suggest there is more to it than this. More even than simply a need to ensure the tyre reaches an adequate temperature, but exactly what is this 'more'?
Does anybody have any quantitative information on how to design in the optimum width of a wheel for a particular purpose (in this case racing) when there have been no outside constraints put upon the design.

RE: Tyre grip

Tires should be as wide, as well as tall, as possible, to allow the largest possible footprint/contact patch to the ground as possible. The R*mu equation only holds good for the actual sliding condition; regular/before slide conditions actually quasi-stationary, since contact-patch (individual rubber blocks) are stationary relative to their nground counterpart area. Therefore, approx. and up to double the adhesion coeff. (mu) can be expected (non-sliding). Inbetween non-sliding and fully-skidding, the descibtor is the skid/slip-angle (phi), the angle between the zero-slip line of the tire, and the actual movement direction of the tire.

See also 'Rubber Science & Technology' and other, for further in-depth and newest research results.

Sincerely,

Soeren Algreen-Ussing, Denmark

RE: Tyre grip

(OP)
Thank you for the reply Soeren, I will also check the reference you gave. However, can I just clarify what you mean. You use the phrase 'adhesion coeff,', are you saying that this is something different & perhaps additional to the 'friction coeff.'? If so, is it a factor related to the area of the contact patch & if so, how? For instance is there a simple linear relationship, is it more complex, or is it so complex that it can only be determined experimentally? Does anybody quote values for this?

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