BMW Ratio Calc

Technical Resources

Gear Speed Calculator

This simple application will be able to calculate the roadspeed for a particular RPM or gear. You can use this to see the effects of raised RPM Limiters, or changes to the gearbox or differential.
First you'll need to calculate the circumference of your wheels.

Width Aspect Diameter
Diameter


Next, fill in the ratios for your gearbox, and differential. Listed below are a number of common settings for various BMWs, but it will also calculate RPM/Speed for any vehicle you have the data on.
First Second Third Fourth Fifth Sixth Seventh
Diff Ratio       


Now that the circumferance of the wheels is known, and the ratios between the engine and road wheels, you can calculate the road speed for any RPM in a given gear

Select your gear


RPM
MPH

Quick Reference

Here you will find a number of ratios and specifications for different cars.

BMW E30
First    Second   Third    Fourth   Fifth   Diff Ratio
316/318i 4sp   3.76 2.04 1.32 1.00 - *
316/316i/318i/320i    3.72 2.02 1.32 1.00 0.81 *
323i/325i   3.83 2.20 1.40 1.00 0.81 *
323i Sport   3.76 2.33 1.61 1.23 1.00 *
M3   3.72 2.40 1.77 1.26 1.00 3.25
M3 Evo   3.72 2.40 1.77 1.26 1.00 3.15
* Check via your year to find the correct ratio.

BMW E36
First    Second   Third    Fourth   Fifth   Sixth   Diff Ratio
316i/318i    4.23 2.52 1.66 1.22 1.00 - 3.38
318iS/320i    4.23 2.52 1.66 1.22 1.00 - 3.45
323i   4.23 2.52 1.66 1.22 1.00 - 2.93
325i 4.23 2.52 1.66 1.22 1.00 - 3.15
328i   4.20 2.49 1.66 1.24 1.00 - 2.93
M3   4.20 2.49 1.66 1.24 1.00 - 3.15
M3 Evo   4.23 2.51 1.67 1.23 1.00 0.83 3.23


BMW E46
First    Second   Third    Fourth   Fifth   Sixth   Diff Ratio
316i    4.23 2.52 1.66 1.22 1.00 - 3.23
316i/318i/320i    4.23 2.52 1.66 1.22 1.00 - 3.38
323i   4.23 2.52 1.66 1.22 1.00 - 3.07
325i 4.23 2.52 1.66 1.22 1.00 - 3.15
328i   4.20 2.49 1.66 1.24 1.00 - 3.07
330i   4.20 2.49 1.66 1.24 1.00 - 2.93
330i   4.35 2.50 1.66 1.23 1.00 0.85 2.93
M3   4.23 2.53 1.67 1.23 1.00 0.83 3.62


BMW E81/87
First    Second   Third    Fourth   Fifth   Sixth   Diff Ratio
120i              4.32 2.46 1.66 1.23 1.00 0.85 3.73
125i    4.32 2.46 1.66 1.23 1.00 0.85 3.23
135i   4.11 2.32 1.54 1.18 1.00 0.85 3.08
118d 4.00 2.11 1.38 1.00 0.78 0.65 3.07
120d   5.14 2.83 1.80 1.26 1.00 0.83 2.56
123d   5.08 2.80 1.78 1.26 1.00 0.84 2.79