RMP's with 4:30 rear diff

[Wayne B]

Need info on RPM's from someone with 4:30's in their rear diff. Also need your tire hight if you know it.

I need RPM's at 65 & 70 MPH with an Auto Trans in O/D.

Thank You Very Much
Wayne B

[Dubco1]

Wayne, you can figure the numbers very accurately with a couple of formulas.

The OD ratio in the 4R100 is .70.

Divide the 4.30 rear gear by the OD ratio (.71) and you get the final drive ratio, 3.05.

Use the following formula and insert the MPH you want to know the RPMs at.

RPMs = MPH X 340 X gear ratio - divided by - tire diameter.

RPMs = 70MPH X 340 X 3.05 = 72590. Divide by 33 inch tire = 2199 RPMs.

Now the first number wont change until you change the MPH. So take the 72590 and divide by a 37 inch tire = 1962 RPMs at 70 MPH.

That should tell you what you want just by changing tire size and MPH.

FOMOGO