mid-drive torque is turning my rear wheel

[WilliamT]

I have a mid-drive unit that I have hooked up to my vintage bike. Sometimes I notice the rear axle has moved causing the wheel to be a bit to the left (side opposite the chainring). I replaced the rear quick release with a bolt on skewer but that doesn't seem to be enough to keep it from moving.

Because the frame is so narrow near the cranks (originally came with 700-19c tires), now fitted with 700-25c. Any movement could cause the wheels to rub the frame. So far it hasn't come to that, thanks to the skewers, but I do notice the slight movement of the wheel as my gears don't shift perfectly from 3-4. I'll have to center the wheel again and adjust the barrel again.

Anyways, I was thinking maybe there was a way to put a chain tensioner near the axle to keep the torque from turning the wheel. A rear torque arm wouldn't work here as I'm working with a skewer. Maybe adding a washer to the skewer clamp may help over more surface?

 

[WilliamT]

For now, I just loosen the centering bolts on the rear dropouts and pulled the wheel back some. That give me a little more room near the cranks.

 

[rich c]

You can definitely buy chain tensioners. A classic situation of over powering the original engineering intent. No engineer intended to have a bicycle used like a scooter.

 

[mikeschn]

That's steel, right? More flex in steel than aluminum... Could be why your stays are moving! You were not clear if the movement was temporary or permanent.

 

[WilliamT]

Yes, its steel. I always check the gap between the frame and rear wheel before each ride. I usually keep PAS at 2 out of 5 and always pedal and never throttle. I use a 38t chainring so its pretty easy for me to get going from a start. I don't feel the motor helping until maybe a few feet later. That's why I'm surprised it had enough torque to move the skewer.

 

[Jason Knight]

Your dropouts look a bit rough and corroded. Corrosion can act as a lubricant. You also seem to have no washers which can help a lot by adding friction if you use the right type.

I'd suggest taking a wire brush and some rust remover to the dropouts, cleaning when finished with soap and water and pat-drying, following up with IPA just to be sure any oils are broken down and it's "really dry". Then I'd add some lock washers (wedge, not tooth or split) and more robust nuts.

Really though this is why I hate quick-release / skewer style hubs. Well, on top of the fact it just makes it easier for people to steal your stuff.

As a last resort, I'd switch to a normal nutted hub. Dimes to dollars that along with a cleaning would clear up your problems.

 

[mikeschn]

Your dropouts look a bit rough and corroded. Corrosion can act as a lubricant. You also seem to have no washers which can help a lot by adding friction if you use the right type.

I'd suggest taking a wire brush and some rust remover to the dropouts, cleaning when finished with soap and water and pat-drying, following up with IPA just to be sure any oils are broken down and it's "really dry". Then I'd add some lock washers (wedge, not tooth or split) and more robust nuts.

Really though this is why I hate quick-release / skewer style hubs. Well, on top of the fact it just makes it easier for people to steal your stuff.

As a last resort, I'd switch to a normal nutted hub. Dimes to dollars that along with a cleaning would clear up your problems.

I second that. It sounds like the skewer is not exerting enough clamping pressure. Get better skewers and/or add locking washers.

 

[harryS]

It's been a while since I fiddled with skewers. Can't they be replaced with a thru-axle?

 

[WilliamT]

I did clean up the drop out but it still wasn't gripping that well. Forgot to mention that I had to widen the rear dropouts to support a 135mm wheel so that may also be a factor.

Anyways, I got the chain tensioners and they seem to do a good job holding the wheel in place. Now I can easily center the wheel just by turning the bolts. With the tensioners in place, I don't even need to tighen the skewer that much; no more than a regular quick release. The tensioner bolt that presses against the frame fits in the place where the original adjustment screw was located so the tensioner doesn't move.



After all this, I missed riding it without all the extra weight of the kit, so now its back to being a regular bike.