Tyre grip

[slaphead]

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.<br>
Consequently the maximum cornering & braking accelerations of a car are simply mu*g (assuming no aerodynamic effects).<br>
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'?<br>
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.<br>

 

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.<br>
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See also 'Rubber Science & Technology' and other, for further in-depth and newest research results.<br>
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Sincerely,<br>
<br>
Soeren Algreen-Ussing, Denmark

 

[slaphead]

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?<br>
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[34V]

I have asked this question also here is a place where a independant phyisist talked
about this. It is long ,other wise I'd write it
here.

http://members.home.net/rck/phor/index.html