Simple. It doesn't. They have the same contact area, just different
length & width dimensions. More width x less length = same area.
Let me repeat: wider tires do not give you a bigger contact patch (unless
you also lower the tire pressure). They just change its shape. It just
happens that the shape makes a difference.
See some of the Road & Track tire test articles for a thorough
explanation. But I think you can see how the contact patch might have
different characteristics along its long dimension (width on a wide tire,
length on a skinny tire) than along its short dimension. The fact that
the tire sidewalls tend to roll under lateral force has a more adverse
effect on the skinny tire, for instance. And the buildup of a wave of
water or snow in front of the leading edge of the tread has a greater
effect on the wide tire, in that it is easier for the buildup to escape
to the side of the skinny tire.
wizardz had this to say:
>Again.... not quite. .....circumferences being the same...
>if properly inflated, both a narrow and a wide tire, of the same size tire,
>are going to have the same size lengthwise contact dimension.
>why else (how else) could widening a tire give more contact area.
>Matt is right. Tire pressure and weight of car are the determining
>factors of contact patch size. Wider tires just make it a different
>shape; i.e. extended crosswise. But for the purpose of snow braking, it
>may very well be that you want the patch extended lengthwise, as it would
>with narrow tires.
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.