I have a Schlumpf Mountain drive 2 speed crankset,
it's planetary reduction gear
really drops the equivalent chainring size a lot .
Mine is on my Brompton, others have fitted them on bigger wheel bikes
and used 2 chainrings.
On My Brommy I have what is a wide range 6 speed ,
the 3 hub gears are used twice.
It's chainring a 54t, the low range is as if a 21.6 tooth,
[50 divides evenly, so a 20t in low range]
and with both gears planetary, double.. gear/range shifts happen,
even bogged down on hills.
Last edited by fietsbob; 03-30-12 at 12:15 PM.