I did say coefficient of friction, which is independent of contact area for the purpose of the F = Mu * N equation, yes. What I said was that reducing the contact pressure allows this COEFFICIENT (Mu)to increase. So while the area does cancel out, the coefficient changes, giving higher grip. In real life the coefficient of friction is not a fixed quantity, but varies with contact pressure among other things. Increasing the width of a tyre generally increases the area of contact, thereby reducing the contact pressure exherted onto the road from the tyre (it depends on inflation pressure and carcass stiffness (rigamortis? is that you?)). According to Tony Foale, reducing the contact pressure generally increases the coefficient of friction. He states a rough figure of halving the vertical load[1] gives a 10% increase in the coefficient of friction. I'm not sure of the mechanisms behind this phenomenon. It could be a probabilistic thing in that by increasing the area on the road you are increasing the chances that more of the contact patch will lie on a good part of the road (as opposed to a small hole, or a loose piece of gravel). This assumes that the road is more good than bad so is probably invalid for Australian roads. It could be something completely different, and probably is. What makes all this shit so complicated is that pretty much all of the relations are non-linear, and they all depend on the specific conditions of the problem, so data about a particular bike on a particular day (at a particular acceleration on particular tyres at a particular pressure on a particular surface) will not be valid if the temperature changes, or the rider changes etc. When I was looking for tyre data for my thesis, I couldn't get any. Testing with a competent rider is probably the most useful way to develop these things, and it's kinda hard to measure the contact area while a bike is being ridden, so raw data is scarce. Yes rubber is bloody perculiar but I can't tell you in exactly what specific ways it's perculiar. I wish I knew but there's still a bunch of research being done on grip mechanisms and a heap of stuff not known about them. Mark [1] That's not to say that by halving the load we're halving the area, this is another of those nasty non-linear relationships
