Up: Table of Contents Reverse-engineering calculations for this hub
SRAM i-Motion 9[1]                                
  Number of gear teeth               Number of gear teeth                  
Gear Sun Gear 1 Pinion to Sun 1 Pinion to Ring 1 Ring gear 1 1=R to P, P to S 2=Direct, 3=P to R   Gear Drive Ratio Stage 1 drive ratio as fraction First stage ratio modified Sun Gear  2 Pinion to Sun 2 Pinion to Ring 2 Ring gear 2 Path: 1=R to P, 2=Direct, 3=P to R Gear Drive Ratio Stage 2 drive ratio as fraction Total Drive Ratio[2] Total drive ratio as fraction Ratio incre- ment Mfr's ratios
1 27 22 22 72 1 0.727    8/11 -0.458 51 16 16 81 3 2.588 2   10/17   0.542   161/297    0.542
2 27 22 22 72 3 1.375 1   3/8    57 9 16 81 1 0.444  243/547 0.621    4376/7049   1.145 0.621
3 27 22 22 72 1 0.727    8/11           2 1.000 1           0.727    8/11 1.172 0.727
4 27 22 22 72 1 0.727    8/11 -0.458 51 16 16 81 1 0.614   27/44 0.853[3]      99/116    1.173 0.853
5 27 22 22 72 2 1.000 1                  2 1.000 1           1.000 1           1.172 1.000
3 27 22 22 72                       1.172[4] 1  17/99 1.172 1.172
7 27 22 22 72 3 1.375 1   3/8            2 1.000 1           1.375 1    3/8    1.173 1.375
8 27 22 22 72 3 1.375 1   3/8    57 9 16 81 1 0.444  243/547 1.611 1   2673/4376   1.172 1.611
9 27 22 22 72 1 0.727    8/11 -0.458 51 16 16 81 2 1.000 1        1.845[5]    297/161   1.145 1.844
[1]
John Allen:
I counted teeth of a Nexus Rad Band hub.
Information about the operation of this hub is at http://bike.shimano.com/publish/content/global_cycle/en/us/index/tech_support/tech_tips.download.-Par50lparsys-0020-downloadFile.html/13)%20Structure%20and%20Function%208%20Speed.pdf
[2]
John Allen:
This is the product of the ratios of the two stages.
[3]
John Allen:
This is the final gear ratio after the second stage, reflecting the rotation of its sun gear by the first stage.
[4]
John Allen:
This is the final gear ratio after the second stage, reflecting the rotation of its sun gear by the first stage.
[5]
John Allen:
This is the final gear ratio after the second stage, reflecting the rotation of its sun gear by the first stage.