RE: Speedo Error, was Dammit part II

["Lin, Gary" <Gary.Lin@wang.com>]

All cars have a built in descrepancy between actual speed (computer is
close) and the speedometer for liability purposes due to mechanical
variations, etc.  Say you got a ticket for 71 mph when it only read 70,
imagine the lawsuit.  So most mfrs. make speedos run high, about a couple
over at all speeds.  I agree that 3 mph over between 20 and 50 is a bit
much.  The OBC will always be pretty close, from 1 over to actual.
Resetting it at a constant speed like w/ cruise on level ground is about
true speed.  Tire wear between new 10/32" and 2/32" will account for no more
than 2% variation at 60 mph.

Gary Lin