good question. I've often wondered the same thing. I think the tread pattern may have determine the "shape" of the contact patch (or a term something to that effect). I remember once on two wheel Tuesday on Speed Vision, they were talking about this, but I walked in on the tail end of the explanation.
Originally posted by kapeXracer does more grooves mean more instablity?
That's why race tires are all "slicks" except of course for wet weather tires. The more rubber that contacts the pavement, the more traction provided. The grooves are there to provide channels for the water to be pushed away from the tire contact patch.