why not properly recalibrate your speedo

you know the wrong size also screws up your odometer and trip meters as well.

check the back of the gauges and look for an adjustment potentiometer, failing that change the gear on the speed sensor (costs $8 you subtract 1 tooth for every 3% gain you'd like)

failing that you can can get a digital adjustment module from Dakota Digital.

Dakota Digital SGI-5:
http://www.dakotadigital.com/index.c...rod/prd126.htm
That thing will let you tweak your speedo exactly.

When I'm driving, the last thing I want to do is math in my head to figure out what my gauges are saying