The Michelin Pro4 Grip clincher
The Pro4 Grip has a few features designed to keep you rolling in the wet. Sipes are cut into the tread, not to clear water as many might think, but to increase pressure and therefore grip by reducing the contact patch of the tire. Margadonna gave the analogy of a football player with a size 14 shoe and a little girl with a high heel; "the girl's heel is putting more pressure on the ground because the contact patch is much smaller," Margadonna said.
Of course a soft rubber would squish and negate some of that benefit, so a higher-durometer rubber is used.
Grip in the wet, Michelin claims, is 15 percent better than the regular Pro4.
Wut. I get pressure increases as area decreases. But I thought more tyre on floor would = more grip. Pressure would decrease of course, but I assumed the extra area more than made up for that.
Hmm. Perhaps they are referring to an ideal world with no road debris. Whereas, with a few little stones around, a lower pressure tyre would be ok (mould around the grit / stone whatever, and still touch the ground) but a really high pressure would hit it, be in contact with only the obstacle, and slide out.