Alfine 11 design
So the other day it occurred to me how Shimano arranged their planetary gearsets in the Alfine 11. (I might be the only person who finds this interesting.) Hopefully I am not repeating something that has already been posted. I've been goofing around with hub ratios in Excel and found http://johnsallen.com/gears/hubratios.htm to be really helpful. Anyway, looks to me like they basically started with the design of a Nexus 7 and started improving things.
So, on Nexus 7 there are four sets of planetary gears, each one of which is only run "one way", that is, to increase or decrease the ratio, and not both. If we call these gears A, B, C and D we have:
1: 1/A
2: 1/B
3: C/A
4: C/B
5: D/B
6: C
7: D
Note that A ~= D and B ~= C.
Now for Alfine 11 we also have four sets of planetary gears, and A ~= D and B ~= C as before. They just allow 3 of the 4 to run both ways.
1: 1/A * 1/C
2: 1/A
3: 1/B
4: C/A
5: C/B
6: D/B
7: C
8: D
9: B*C
10: B*D
11: A*D
My spreadsheet can fairly closely replicate the 7 "derived" gears starting with the ratios of 2, 3, 7 and 8.
The Nexus 8 / Alfine 8 are totally different. They also have 4 sets of planetary gears, but obtain their ratios as folllows:
1: 1/A
2: B/A
3: C/A
4: D/A
5: 1.0
6: B
7: C
8: D
So there you have it, for what's it worth. Now, owners of the Alfine 11 can obsess about just how many planeteries are spinning around while they charge a hill.
