Torque Arm Question

[AxialFlux]

So I started on my 500w rear hub Townie conversion this evening, and ran into a slight problem with the torque arm. If I install enough washers so that the bolt doesn't hit anything, I am left with what I think is very little thread for the axle nut to tighten onto. It does thread on it, but I don't think I would ride it like this. Maybe I am missing something, or possibly have the arm on incorrectly, who knows. I did notice that there are "keyed" washers that go between the hub and frame, but I think I would feel safer with the torque arm on as well.

Here are a couple pics:

 

[harryS]

I agree with you, the axle nut needs a couple of threads exposed for margin. You will end up stripping what threads do make contact if you use it like that.

You should turn the arm so that its mounting screw won't hit the frame, and this will allow you to place the arm directly against the frame. Then I would put a thin washer over the arm, I've done several hubmotors with only that tabbed washer, a torque plate and a washer under the axle nut. You'll have to relocate the second arm of the torque arm to be under the frame, rather than on top where it is now,

I had two commercial ebikes with rear hubmotors and alloy frames, and neither used torque arms, but I've always had at least one arm on my converted bikes.

 

[Sierratim]

I always used torque arms on my DIY conversions, but the axle nuts always engaged fully with the axle threads. No need to go beyond the axle threads for full strength, but every thread in the nut counts so engage every one.

Yours aren't fully engaging. Too many spacers? Hard to tell from the pics.

 

[AxialFlux]

I agree with you, the axle nut needs a couple of threads exposed for margin. You will end up stripping what threads do make contact if you use it like that.

You should turn the arm so that its mounting screw won't hit the frame, and this will allow you to place the arm directly against the frame. Then I would put a thin washer over the arm, I've done several hubmotors with only that tabbed washer, a torque plate and a washer under the axle nut. You'll have to relocate the second arm of the torque arm to be under the frame, rather than on top where it is now,

I had two commercial ebikes with rear hubmotors and alloy frames, and neither used torque arms, but I've always had at least one arm on my converted bikes.

Annnnd....I feel like an idiot. Rotated it around, and was able to get rid of a couple washers. Ended up with this:

 

[Sierratim]

and... success!

 

[AHicks]

My opinion, there's noting written in stone about you having to use that hose clamp to fasten the torque arm to the frame. I don't care for them myself.

I think maybe you might have a much sturdier setup if you didn't even use that second piece. Just use one of the existing bolt holes to hold the part that goes over the axle (like you show in that first pic). That single bolt is going to provide a much sturdier mount than that hose clamp could ever hope for....

 

[harryS]

I agree with AHicks, but I've spent many a winter evening shaping a DIY torque plate. Then I drill the mounting hole in the wrong place and I have to start over. This one was a success.

 

[Marcela]

There is a low profile lock nut that can sometimes be used in place of the std height.

 

[AxialFlux]

My opinion, there's noting written in stone about you having to use that hose clamp to fasten the torque arm to the frame. I don't care for them myself.

I think maybe you might have a much sturdier setup if you didn't even use that second piece. Just use one of the existing bolt holes to hold the part that goes over the axle (like you show in that first pic). That single bolt is going to provide a much sturdier mount than that hose clamp could ever hope for....

I think I will look into this, as the hose clamp looks janky. Plus, sturdier is better.