contact patch

["R. W. Zehr" <rzehr@pacbell.net>]

Uh, maybe basic physics or math has a leak somewhere, but if a tire is
at a constant pressure in lbs/sq.in., and is supporting any given amount
of weight, its contact patch in sq.in. will be the weight divided by the
pressure. This assumes a bald tire that is constructed like a balloon,
where the tread pattern is not an issue.

What changes when changing a rim, or a tire, given the same tire
pressure AND TREAD PATTERN is the SHAPE of the contact patch. Narrower
tires have a longer, narrower contact patch, while wider rims or tires
will have a wider, shorter patch, but the total size of the contact
patch remains the same...

The only difference in this re. dynamic changes in contact patch size
during cornering are that the outside wheel temporarily gets a larger
contact patch because there is more "weight" on it due to the force
vectors resulting from turning, but guess what - the tire pressure
increases to match it, and again, the contact patch size is weight
divided by tire pressure (albeit larger on the outside tire, because
both pressure and weight are larger). 

Given the same turning radius and speed, the contact patch of a wider
tire/rim will be the same size as that of a narrower one under the same
turning forces, albeit wider and shorter, and thus less likely to slip
sideways...

Tell me if I'm wrong (I know someone will...)
Rick Zehr