Calculate speed vs RPM calculator (based on transmission, gears and tires)
The purpose of this page is to determine a vehicles speed or engine speed based on different transmission gears, differential gears, and tire sizes. It is most useful when changing tire size or differential gearing to see its effect on engine speed or mph in each gear.
This program is different from 90% of the other calculators out on the internet in that we use "Revolutions per mile" not just a height in inches. The reason for this is because tire height in inches calculated based on the tire size (e.g. 235/85R/16) can be off by several MPH.
Two tires of the same size can have *different* actual mounted/measured heights that will throw off your accuracy by several miles per hour.
Revolutions per mile can be obtained by the tire manufacturer. TireRack also has a lot of the revolutions per mile listed under "specifications."
Is your transmission/tire not listed? e-mail me and I will add it!