And here's one to calculate speed and or RPM given your ratios and tire diameter.
http://www.onlineconversion.com/bigger_tires.htm

A "tall looking" 16" tire might be 31" tall unless its a real big wide one. Measure to know for sure, or look up your exact tire info from the manufacturer and see what the loaded radius is, or revolutions per mile, or close enough is the listed outside diameter.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-