I think we still need more info to make the calculator work out (guessing you are referring to the one in this Calculate RPM Tech Tip ).

What transmission are you using (output final drive)? If you have an overdrive transmission, that affects the output RPMs.

What is the overall height of your tire (not all 235/70/15's measure the same)?

EDIT: Kevin beat me to the punch. Still need to confirm on the questions I asked though as they can make a difference. smile

Last edited by Gdads51; 11/05/2023 11:55 PM. Reason: added info
~ Dan
1951 Chevy 3 window 3100
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