3rd party..
then there are 2 speed single chainring cranksets...
Some made For Brompton, not made by them..
the gears are between the arm and the chainring.
so arm rotates at a different rate than the chainring.
1.6x overdrive a 34t in overdrive acts like a 54t,
I went the other way, 2.5 :1 reduction gear, so my 54t acts like a 21.6t
and I go through my BSR gears twice , 3rd, high in low range, 4th low in high range..
both planetary, so shifts at any speed, even bogged down on a hill..
Over the bar shifter shifts easily from 1 to 3 or 3 to 1..
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Last edited by fietsbob; 09-15-18 at 11:26 AM.