You said No matter what the direction of the tyre' date=' if the casing isunidirectional and the rubber uniform front and back, the co-efficient of friction is the same no matter which way the tyre faces. Therefore the only differences there could be lie in mechanical adherence between tyre and substrate. These are negligent in a so-called unidirectional tyre since the pattern cannot be so much different in its two faces. But more important, mechanical adherence or interlocking of tyre and surface irregularities is higly dependent on the surface. Very few surfaces are shaped like the negative of a tyre print. It is largely moot. [/quote'] Firstly, unidirectional tyres generally won't have a uniform tread pattern. They are not labelled unidirectional because of concerms regarding the integrity of the casing, but merely because the tread is designed to be more effective in a specific direction. If the tread is uniform, it's not a unidirectional tyre and thus there will not be any difference whichever way you fit them. Also, the surface does not have to be shaped like the tyre to effect grip. It's simply a matter of fact that on virtually any given surface a genuine unidirectional tyre will have varying differences in grip depending on which way it's installed. The only surfaces excepted being something solid like tar or cement where the difference will probably be unnoticable. On something like a soft, loamy forest floor where the tread can (to varying degrees) be forced into the surface, certain tread pattern will grip better and some will slide. In the same way that an aerodynamic shape will slice a cleaner hole through the air, certain shapes of tread will slice through the surface/ground easier, commonly experience as a loss of traction.
