Originally Posted by Joe H
I run a 3.08 gear with 235/75R15 radials, ( 28" tall tire ). 250 ci engine, T-350 automatic transmission with 1-1 final drive. At 70 miles per hour the engine is running 2550 - 2600 rpm. Around town is just fine, truck weighs 3150 lbs so probably lighter then yours. I had a 3.42 for awhile, and yes it was quicker from a dead stop, but highway driving was a pain due to high rpm ( 3000 rpm ) and the constant attention to maintaining speed. At much higher rpm, even the littlest throttle change would speed up or slow down the truck, once I got the rpm down with the gear change, it is much easier to maintain a constant speed.
Calculator: https://www.randysworldwide.com/calculators/rpm/

When you are talking about a manual starting out with a load in first gear, automatics are different because you have a torque converter, but none the less good info there.
A vacuum gauge can help you determine fuel efficiency. Like another has said a too tall a gear just to get your low cruising rpm might not be the most economical.

Last edited by sstock; 07/04/2018 2:58 PM.
1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration