Can the 3 speed be retrofitted to become a 6 speed (or whatever)?
1, The Driver is wider to take 2 cogs + spacer between them...
The BWR internals and driver are different from the BSR/AW3.
the Sachs hubs used a variation of the 3 spline cog .
Im Using a 15t cog made for the Sachs 3 by 2 on my BSR, currently..
it differs slightly from a standard S-A cog. in being thinner , and 3 of the 15t
are shorter to act as a shift gate.. [the cogs seen in 1st example, above]
the newer hub driver in the BWR is a Shimano BMX free-hub like spline.
and the toothing is sort-of hyperglide like..
rear wheel can be rebuilt/replaced, [2nd example , above]
but the frame has to have the brazed on fittings for the shift mech to fit upon.
Ie, Type 3, and subsequent, production..
I bought a Schlumpf Mountain drive, it's 150% lower second ratio
is such that I use the 3 hub gears twice.. (no overlap or 1/2 step)
[its like a 50-20t, but a planetary so a pretty fast shift.. ]
Swiss mountains..