Rpms tire size and different rear axle ratios graph

[danliveshere]

Guys I seem to recall years ago seeing a graph on here that someone posted that showed the effects of different rear axle ratios , tire sizes and rpm at a certain speed. I can’t find it.
Has anyone got access to that? Thanks Dan

[danliveshere]

I found this over on the hamb

[HDowse]

I’ve used this website. Plug in values for tire size, differential ratio, RPM, speed. Plug in any 3 values to get the fourth.
http://www.advanced-ev.com/Calculators/TireSize/

[rotorwrench]

If you have the 1950 revision (green bible) of the Ford chassis parts catalog from 1928 to 1948, you will find a basic chart in there for the speedometer drive gearing.

[38 coupe]

There have been several threads about axle ratios, engine speed, and road speed over the years. One thread that had lots of discussion is this one: https://fordbarn.com/forum/showthrea...5747&showall=1


For quick reference in this thread see the table below. Since this table is probably not easy to read in this forum I have also attached this as a pdf, which you can download for easier viewing. All these ratios are for 28 inch tall tires.

[HDowse]

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38 Coupe, thanks for that comprehensive chart. I have a 26% Mitchell in my 40 DeLuxe with a 4.11 rear end it's interesting to see the rpm drop in overdrive.

[danliveshere]

Yes thanks for the pdf, great chart!
My buddy is building a blown flathead, 3 speed with an 8” rear axle, he’s trying to figure out the best ratio to suit his setup. Dan.