The challenge of mounting a hub without stretching / filing the frame.

[kyle47]

Hi All

Looking for a small lightweight hub motor (of the likes of Q75, Xiongda, Q100, FX08) on a commuter bike, preferably rear. Frame is a alloy, from a vintage MTB with 130 mm spacing between dropouts and 10mm diameter dropouts. The bike is for 26 inches v-brake wheels (no disc).

I believe the challenge of of fitting in a 130mm (without stretching, I know we can stretch but the challenge is not to stretch) can be addressed by buying a freewheel motor with a ~135mm OLD and switch to a slimmer freewheel (e.g. 5 speeds, or even single speed!) and removing or grinding spacers on the transmission side. Did I get this right?

Regarding dropouts, it seems that most hubs have 12mm axles but standard axles are 9.8mm or so in 10mm dropouts. Are there any hub motor with 10mm axle to avoid the the need to permanently file the frame?

Many Thanks

 

[Sturmey]

Hi All

Looking for a small lightweight hub motor (of the likes of Q75, Xiongda, Q100, FX08) on a commuter bike, preferably rear. Frame is a alloy, from a vintage MTB with 130 mm spacing between dropouts and 10mm diameter dropouts. The bike is for 26 inches v-brake wheels (no disc).

I believe the challenge of of fitting in a 130mm (without stretching, I know we can stretch but the challenge is not to stretch) can be addressed by buying a freewheel motor with a ~135mm OLD and switch to a slimmer freewheel (e.g. 5 speeds, or even single speed!) and removing or grinding spacers on the transmission side. Did I get this right?

Regarding dropouts, it seems that most hubs have 12mm axles but standard axles are 9.8mm or so in 10mm dropouts. Are there any hub motor with 10mm axle to avoid the the need to permanently file the frame?

Many Thanks

Hi and welcome. You have brought up three separate issues in your inquiry which I had when fitting a rear wheel to an older bike. The first is about stretching the frame which I agree with you should be avoided if possible. However there is a bit of a 'spring' in the frame and its often possible to stuff an axle a few mm wider into a narrow frame, although it does make wheel fitting a little more difficult.
The second issue is about fitting a more narrow freewheel. This works only to a point, as the axle is not always threaded the whole way in, as shown in photo below. I fitted the hub using a six speed freewheel and fitted the tabbed anti rotation washer on the outside of the frame (tab facing inwards) on the freewheel side, rather than the inside. I think I may have had to reduce the dishing (spoke adjustment) a little to center the wheel.
The third issue is about the dropouts. The axle was 10 X 12 (which is common for 250w geared motors), so I filed the dropouts deeper to accommodate both the axle and the anti-rotation washer tabs. In my case, the dropout U channels needed to be made deeper by about 4 or 5mm, but this was not a problem as dropout was solid.
Best of luck.
PS Perhaps take and upload a photo of your rear wheel dropouts and you may get a better opinion.

 

[Nealh]

My Bafang G370 is a 10 mm dia axle, it fitted into my Surly disc trucker forks very nicely with no need to file. One has to select the correct motor and check the specs to see which might fit. G370 I have only seen as a front option.

 

[Nealh]

Q100 is 12 x 10 so will need some fettling if the d/o seat isn't deep enough, as indicated most geared hubs are 12 x10 with very few being much smaller.

 

[harrys]

Q100's use two bushings and a nut under the freewheel to set the width. I've used a 6speed freewheel and cut one bushing to fit a 130mm dropout.