Ok, so I just received a GM mini rear hub and test fitted a standard 6spd junk shimano freewheel similar to the freebie ones you get with rear hub motors. I was bummed because it barely left enough room for the chain, and I was hoping that magically I'd be able to fit a 7 speed on this hub. Its going on an aluminum frame so I can't really widen the dropouts. I measured the GM mini, and its 100mm between the left mounting surface, and the freewheel mounting surface on the right. That leaves 35mm for the freewheel and chain.
So I dug out some old freewheels to compare the spacing. 2nd up was an IRD 6spd freewheel which had narrower spacing. It looked like another gear would fit with a hub motor. This is when I looked it up online and learned about how 6spd freewheels came in standard and "ultra" spacing, as well as configurations for 126mm and 135mm dropouts. I pulled an IRD 7spd freewheel off an older bike, and spun it onto the GM mini hub and it clears the mounting surface on the axle!
I believe this is a viable option for most hub motors out there. The Shimano 6spd and IRD 7spd are very close to similar widths. There's maybe ~1mm difference so at worse you might have to run a narrower chain to clear your dropouts, or add a thin washer. I tested a 7 speed chain and it it appears to clear, but I will probably use a 9 spd chain instead.
The nickel plating on the IRD freewheel also matches fairly well with the polished GM mini.
So I dug out some old freewheels to compare the spacing. 2nd up was an IRD 6spd freewheel which had narrower spacing. It looked like another gear would fit with a hub motor. This is when I looked it up online and learned about how 6spd freewheels came in standard and "ultra" spacing, as well as configurations for 126mm and 135mm dropouts. I pulled an IRD 7spd freewheel off an older bike, and spun it onto the GM mini hub and it clears the mounting surface on the axle!
I believe this is a viable option for most hub motors out there. The Shimano 6spd and IRD 7spd are very close to similar widths. There's maybe ~1mm difference so at worse you might have to run a narrower chain to clear your dropouts, or add a thin washer. I tested a 7 speed chain and it it appears to clear, but I will probably use a 9 spd chain instead.
The nickel plating on the IRD freewheel also matches fairly well with the polished GM mini.
