Hydroplaning again

[C M Smith <cmsmith@domain.elided>]

Er guys, contact patch area for a given car weight and tire pressure will 
be approximately the same regardless of tire profile. What changes is the 
shape of the patches. Narrower tires have the same contact patch pressure 
per square inch give or take a bit. The reason a narrower tire hydroplanes 
less readily than a wider tire is frontal area not psi on the ground. The 
leading edge of the narrower tire has less water to push out of the way so 
less upwards force is exerted on the tire.

That's why it's important to have rain grooves circumferentially, 
especially down the center of the tread. The water "sees" this as two or 
more tires coming down the road. If you want good dry road grip as well it 
helps to have angled "tusk" shaped grooves to allow the water in the 
circumferential grooves to get squirted quickly out the side of the tread. 
Look at a Formula One rain tire...perfect compromise between good 
circumferential grooves for water cutting and angled grooves for water 
removal while preserving some modicum of tread stability. Rather like the 
Pirelli P7000, the Michelin Pilot, and even the old Goodyear Rain Tire.

If you guys all drove in snow, heavy snow, light snow, slushy snow, dry 
snow, etc etc you'd have a clear understanding of this relationship.

Wide short contact patches exert the same total pressure on the road, it's 
only when the tires move forwards that the dynamics change. Then the wider 
tires are pushed up by more force due to more water hitting the leading 
edge. Or snow etc.

Cheers

Michael

Michael Smith
Calgary, Alberta,Canada
91 Alfa 164L

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