I'm just doing some napkin calculations on the gearing here.
Assuming what another owner said about spacing is correct (
7 sprockets/speed using thinner 9-speed parts) you could theoretically use even narrower parts as long as they adhere to the Shimano HG standard.
So assuming:
- 7-speed uses 1.8mm thick sprockets spaced 5mm apart.
- 9-speed uses 1.78mm thick sprockets spaced 4.34mm apart.
- 7-speed uses 1.6mm thick sprockets spaced 3.74mm apart.
That would mean the bike currently has
7 speeds at a total width of 38.5mm. (
as opposed to 42.6mm if it was using 7-speed parts)
Meaning, that you could fit
8 speeds using 11-speed parts for a total width of 38.98mm!
9-speeds would probably be too much at 44.32mm but could theoretically work if they did use 7-speed parts.
Something to ponder and measure!
EDIT: And then there's the
SunRace MZ90 12-speed (MTB) and
CSRZ800 WAV,
WAT and
WAW HG-compatible 12-speed models...
9-speed in 42.8mm anyone?
Source:
Obike.de