How do I calculate "development" and "inch gears"?
For the calculation, you need the following details:
- Tooth number of the chainring
- Tooth number of the rear cog
- Circumference of the rear wheel (= diameter * 3.14)

You get the "development" by the following formula:


Tooth number of the chainring / tooth number of the cog x circumference of the rear wheel (in meters)

You get the "inch gears" by the following formula:

Tooth number of the chainring / tooth number of the cog x circumference of the rear wheel (in inches)/ 3.14

For a derailleur system, calculate all gears according to the formula above.

For a rear hub, multiply all results with the following factors:

3-speed-hub:
1.speed: 0.75
2. speed: 1
3. speed: 1.33

5-speed-hub SRAM Spectro 5:
1.speed: 0.67
2. speed: 0.78
3. speed: 1
4. speed: 1.28
5. speed: 1.5

7-speed-hub SRAM Spectro 7:
1.speed: 0.57
2. speed: 0.68
3. speed: 0.81
4. speed: 1
5. speed: 1.24
6. speed: 1.48
7. speed: 1.74

7-speed-hub Shimano Nexus 7:
1. speed: 0.632
2. speed: 0.741
3. speed: 0.8431
4. speed: 0.989
5. speed: 1.145
6. speed: 1.335
7. speed: 1.545

For calculating the speed-drive effect, multiply all results with 1.65.
 
Are you looking for even more detailled infos?
Just download our manual (pdf-file): speed-drive manual english