In a message dated 97-10-18 12:52:22 EDT, tbf@pacifier.com writes:

<<Of course the wheel diameter doesn't make the ratio change higher or
 lower, it is the tire diameter. The Michelin Agilis 51 tires are exactly
 the same diameter as the OEM MXL tires and they fit 15" rims. The extra
 bonus is that they are rated over 1700 pounds of load per tire. The
 shorter sidewall should mean a more stable tire on the road (someone
 mentioned that awhile back).  >>

Yes, a larger wheel diameter doesn't necessarily mean a larger tire diameter,
but (as I was assuming) staying with the same tire profile the 15" tires will
be larger.  A 70 series tire on a 15" wheel will be about 1" larger than a 70
series tire on a 14" wheel.  If you go from a 14" wheel with a 70 series tire
to a 15" wheel and a 60 series tire you'll maintain approximately the same
overall diameter.  This is known as a "plus 1" setup.  Going further to a 16"
wheel and a 50 series tire is a "plus 2" setup.  Using the lower profile 60
or 50 series tires will (as Todd points out) improve cornering and overall
handling.  This comes at the expense of ride comfort because the taller
sidewalls have more "give" and can provide a smoother ride.  Off road
performance will also diminish with low profie tires.  A lot of sidewall
provides for a better ability to absorb rocks and keep the rocks away from
the rims where they might unseat the tire from the rim.

Regards,
Jim Davis