The Stovebolt Site Forums The Shop Area Driveline What is the best Transmission for my 54 truck?

Here's some formulas you can use to help get your engine rpm into the right cruise range.

60mph rpm = 20168 x Rear axle ratio x Trans OD ratio / tire diameter

If you don't have the tires to measure, you can estimate diameter with this-

tire diameter = 0.000786 x width x aspect + rim size
where width is the 215, 225, 265, etc number before the R and aspect is the 75, 65, 60 number after the R.

So if you're running 215R75-15 tires on your 3.73 rear end behind a 700R4 with 0.7 OD, you've got a 1900 RPM cruise at 60 mph.

My 235 has peak torque at 2000 so that's be about perfect for me.
In fact I'm running 215R75-15 tires, a 3.90 rear axle and a BW R10 0.70 OD. My 60 mph cruise rpm is just under 2000. Two thumbs up.

regards,
Leon