Originally Posted by
badmother
First of all I said "mountain drive and similar solutions". Maybe I should have said "front mounted internal gears with only one visible chainring (no derailing of the chain)". There is more than one on the market and what they have in common is that you see/use only one chainring but there are gears innside that gives you
the effect of two or more chainrings, just like what happens in a rear hub with one sprocket and internal gears. This is why chain wrap is not an issue!
And about overlap: Did you ever calculate the overlap on a regular 9x3 bike?? Some times you
may want to find the same gear in more than one place on a bike for easyer shifting.
The Schlumpf Mountain Drive and Speed Drive from Harris Cyclery
Perhaps I was not clear to your reading. My comment about chain wrap pertained to an actual 54-22 double, not to the Schlumpf Mountain Drive. Having owned a Brompton with such a driveset now 10 years, I am aware how it is constructed, and its weight and operation. But thank you. As far as overlap on a 9x3, I have seen those gear-inch calculations and am well aware of the redundancies in those setups. But those have 27 steps from which a sequence can be selected to make reasonably even progression without excessive cross-chain stresses. With 12 "gears" across 550% gain (thinking the Brompton with a standard 3x2 + Schlumpf) avoiding redundancy is more important if you want to keep the spacing between gears reasonably short and even (the way other IGHs do--thinking Rohloff and Alfine 11 or 1x 9-12 setups do.)