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
 Circumference

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.

 1. 2. 3. 4. 5. 6. 7. Diff ratio to E46 M3 values

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

 rpm: kmh:

## Quick Reference

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

BMW E30
 1 2 3 4 5. Diff ratio 316/318i 4sp 3.76 2.04 1.32 1 - * 316/316i/318i/320i 3.72 2.02 1.32 1 0.81 * 323i/325i 3.83 2.2 1.4 1 0.81 * 323i Sport 3.76 2.33 1.61 1.23 1.00 * M3 3.72 2.4 1.77 1.26 1.00 3.25 M3 Evo 3.72 2.4 1.77 1.26 1.00 3.15
* Check via your year to find the correct ratio.

BMW E36
 1 2 3 4 5 6. Diff ratio 316i/318i 4.23 2.52 1.66 1.22 1 - 3.38 318iS/320i 4.23 2.52 1.66 1.22 1 - 3.45 323i 4.23 2.52 1.66 1.22 1 - 2.93 325i 4.23 2.52 1.66 1.22 1 - 3.15 328i 4.2 2.49 1.66 1.24 1 - 2.93 M3 4.2 2.49 1.66 1.24 1 - 3.15 M3 Evo 4.23 2.51 1.67 1.23 1 0.83 3.23

BMW E46
 1 2 3 4 5 6. Diff ratio 316i 4.23 2.52 1.66 1.22 1 - 3.23 316i/318i/320i 4.23 2.52 1.66 1.22 1 - 3.38 323i 4.23 2.52 1.66 1.22 1 - 3.07 325i 4.23 2.52 1.66 1.22 1 - 3.15 328i 4.2 2.49 1.66 1.24 1 - 2.93 330i 4.2 2.49 1.66 1.24 1 - 2.93 330i 4.35 2.5 1.66 1.23 1 0.85 2.93 M3 4.23 2.53 1.67 1.23 1 0.83 3.62

BMW E81/87
 1 2 3 4 5 6 Diff ratio 120i 4.32 2.46 1.66 1.23 1 0.85 3.73 125i 4.32 2.46 1.66 1.23 1 0.85 3.23 135i 4.11 2.32 1.54 1.18 1 0.85 3.08 118d 4 2.11 1.38 1 0.78 0.65 3.07 120d 5.14 2.83 1.8 1.26 1 0.83 2.56 123d 5.08 2.8 1.78 1.26 1 0.84 2.79