Originally Posted by
glye
The sunrace hub which accepts 9t cassettes fits only these special sunrace cassettes. Both 10 and 11 speed fit, I have used both. (The old shimano capreo cassettes MAY fit, there is some indication the hub is a clone of those, but they are obsolete anyway.) It will NOT fit standard shimano/sram cassettes. It will also NOT fit sram xd cassettes.
It is also a weak hub in my experience, I can not recommend it for strong and/or heavy riders.
SRAM XD/XDR is a totally other concept than the classic Shimano freewheel and also the Campagnolo freewheel.
But the Capreo, Moulton, Campagnolo N3W and I think this Sunrace use all the same idea: the part of the freewheel close to the spokes where the biggest cogs are located remain classic. But the extremity where the smallest cogs come has a smaller section to allow the 10 or 9 teeth cog. Campagnolo has an adapter that allow the use of the classic Campagnolo cassettes on the N3W freewheel.
Therefore my question if it is really impossible to mount a classic cassette on the Sunrace freewheel.
I read the problem you had with this Sunrace rear hub, but this is the only remaining derailleur option for the R&M Birdy.