The previous thread about engine RPMs and top speed got me thinking and I
was hoping that some of you gear heads out there could  confirm or correct
my calculations.

Here's what I've come up with:

GIVEN....

PI = 3.14159
MILE = 5280'

SPEED = ((((RPM /(Gear * Final Drive)) * (2 * PI * Tire Radius)) / 12 ) *
60) / MILE

Using this formula with the gear ratios (4th gear = 0.85, Final Drive =
4.83) and tire radius (~12") in my 4 speed Vanagon I come up with: ~71 mph @
4,000 RPM.  This sounds dead on for my van.

It also gives me:

~18mph for 1st gear @ 4,000 RPM
~34mph for 2nd gear @ 4,000 RPM
~56mph for 3rd gear @ 4,000 RPM

All these speed sound about right.

Am I missing something?

I'm looking to build a freeway flyer by mixing gear ratios from different
trannys, so this formula could be of great help... if it's correct.

Cheers,

Jeff