To be more specific, 6.17's with 38.5's or 40's, with a 4speed. If so, how are the R's on the hwy?

DISCLAIMER, this is just math, I don't run this combo

I plugged the numbers into my gear ratio spread sheet...

1:1 tranny, 6.17:1 axle ratio

38.5s should turn 3346 RPM @ 60 MPH.
40s should turn 3221 RPM @ 60 MPH.

Tire rotations/mile are computed from from the height of the tire, not the loaded radius, or the radius at highway speed.

computed tire stats are:

38.5s = 542 Rotations / mile
40s = 522 Rotations / mile

If you have Tire rotations/mile from a spec sheet it should be more accurate.

YMMV,

- Dan

well my setup isn't what you want in any way, shape or form but i'm running 5.89's on 35's with a 5 speed and @ around 50mph my motor is spinning about 3500. I say @ around cuz my speedo says were dooin 80+. LOL