Math...check...exactly. <img src="/forums/images/graemlins/smile.gif" alt="" />

30 x PI (3.1416) = 94.248 (circumference in inches)

63360 (# inches per mile) / 94.248 = 672.7 tire revolutions per mile

672.7 x 4.625 (gear ratio) = 3109 engine revolutions per mile in 4th gear

Not knowing the amount of overdrive...just multiply the OD percentage by the non-OD number above.

K? <img src="/forums/images/graemlins/wink.gif" alt="" />

1987 Raider - Roxy
1988 Mighty Max 2.6L Turbo - Pearl
1997 Mountaineer V8 - Freddy
2000 Excursion V10 - Freya