<< I believe, correct me if I'm wrong, that the speedo
is indeed affected by "bigger shoes." If the speedo
measures the revolution of the front wheel, not the
actual speed of travel, then it would display a SLOWER
SPEED on the needle with bigger tires.>>

You're right that the speedo reading is proportional
to the speed of the front wheel regardless of tire
size, and that at an actual speed of 70 MPH the speedo
would read lower as the tire diameter got bigger.
My point was at given engine RPM - say 4000 - as the
tire size increased so would your actual speed. So
you'd be going 77.7 while your speedometer read only
70, say. By increasing tire diameter you effectively
lower engine rpm at a given actual speed. I put
together a whole chart of the relative speed
comparisons of different tire sizes which I posted
some time ago - I'll p-mail it to anyone
who's interested.

Doug Fitz-Randolph