rear axle gear ratio chart

[jimTN]

Sometime in the past someone posted a chart that had rear axle ratios, tire sizes, rpms and road speed data. It included everything from Model A 19" rubber on up thru 15" stuff. I printed it off but its deep somewhere in my piles of paper. If you have such a animal, could you please post it. A friend has a 60 running a 3:78 in a T with 19" A tires and wants to get a more optimal ratio that will put the RPM range around 2500-3000 rpm at 60 to 65 mph.

[JSeery]

It is an easy formula, just calculate it for your parameters.

[Hotrodfil]

Here's a link to mine on google drive.
You can edit it online, or download it as an excel file. Works in Libre office too.

https://docs.google.com/spreadsheets...gid=1208129397

[HDowse]

Here’s the one I use:
http://www.advanced-ev.com/Calculators/TireSize/

[V8COOPMAN]

Originally Posted by jimTN

Sometime in the past someone posted a chart that had rear axle ratios, tire sizes, rpms and road speed data. It included everything from Model A 19" rubber on up thru 15" stuff.

This has got to be the one.....yes, no? DD

[jimTN]

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Thanks to all, the formulas above will work for what I need. That speedometer chart is great but not the chart I am looking for.

[JSeery]

There are a lot of calculators online, but I have seen several of them product incorrect results! I would at least check them against doing it by hand at least once to double check the fill in the blank calculators. It is a very simple formula:

RPM = (MPH X Axle Ratio X 336) / Tire Dia

As an example
60 MPH
3.78 Axle Ratio
30 inch Tires

RPM = (60MPH X 3.78 AR X 336) / 30 TD
RPM = (76,204.8) / 30
RPM = 2,540

[flathead 39]

Originally Posted by HDowse

Here’s the one I use:
http://www.advanced-ev.com/Calculators/TireSize/

Thanks, this is eactly what I need to decide whether to change my 3.78 to 3.55 or 3.25.