There is a potential for error in these calculations with bias-
belted tires due to centrifugal force expansion of the tire at
high speeds, but that effect is generally negligible for radial-
ply tires due to the circumferential belts used in their
construction. To get accurate results, racers using bias-ply
tires should check with their tire supplier to determine how
much the tire radius will change at various speeds. For those
who are curious about the calculations, here are the gory
details of the speed versus engine RPM calculations: Each
revolution of the engine is reduced by the transmission gear
ratio, each revolution of the output shaft of the transmission
is reduced by the rear-end ratio, and each revolution of the
tire makes the car move a distance equal to the circumference of
the tire. Pretty simple really. Let's go thru the calculations
to create an equation for the vehicle speed... First, let's
define the meaning of the gear ratios: Transmission Gear Ratio
(R1): denotes how many engine revolutions