When To Use Torque Arms

[3wheels1life]

Hi everyone,

As you may know I recently bought a 36v 350w BLDC gearless rear hub motor. Currently I'm shopping for a bike frame locally, and I have a couple of questions for you regarding torque arms...

1. Are torque arms needed for this hub motor on an Aluminum frame (rear forks)?
2. Are torque arms needed for this hub motor on a 4130 chromoly frame (rear forks)?
3. Any other information I should consider when buying the frame?
4. Are there any types of dropouts (vertical, etc.) that are not good for this hub motor?
5. Where can I get some good torque arms?

Again, this is a rear hub motor. I am not planning to overvolt it, mod it, etc.
Thanks in advance for your advice.

-3wheels1life

 

[davec]

with the amount of power you're running - the answer is no
i've run a 36v rig for many months and it was a front/ steel fork with no trouble
you're running 36v on a rear dropout which is considerably stronger than a front fork.....
at high power/voltage it is needed but not for 36v- but i suppose for peace of mind you can always include one... it wont harm anything

 

[Chalo]

If everything else is right about your build, then a torque arm may be optional. But...

That presumes the axle-to-slot fit is very snug, the axle nuts are done up quite tightly (which isn't always possible with interrupted threads and horrible cheap Chinese nuts), you don't use regenerative or active e-braking, and you don't ever suffer mechanically violent electrical failures such as dead shorts or phase shuddering.

Using a torque arm is easier, cheaper, and more convenient than repairing your rig from damage caused by not using one.

 

[wesnewell]

1. I'd use torque arms/plates on any aluminum dropout. That's why i don't use bikes with aluminum dropouts.
2. I've never used a torque arm on steel dropouts and never had a problem. Running 1000W motor up to 4000W at 100V for 10,000 miles.
3. Make sure you torque the axle nuts properly. That's about 100 ft lbs of torque. I also use a jam nut on the back side. Axle nuts have never come loose.
4. Some vertical dropouts are very shallow. Take care if you get this kind.
5. I don't think there's what I'd call good torque arms. If needed I'd use torque plates epoxied nad screwed into the dropouts.

 

[d8veh]

You don't need torque arm, but there's some provisos:

If you have dimpled or recessed dropouts, the first washer must sit completely within recess.
The larger motor axle doesn't go so deep into the drop-out, so consider deepening and/or re-profiling the drop-outs. The motors often come with anti-rotation washers, which can't do anything unless they're actually in the drop-out. Look at the photo below to see what I mean.

The 350w Q100 motor doesn't have much torque compared to a 350w Bafang BPM. i think I'd fit a torque arm fot the BPM but not the Q100.

Fitting a torque arm isn't difficult and they're readily available now, so it's always a good idea to fit one if you can.

 

[dogman dan]

In all cases, the fit of the washers and the axle of the motor to the dropout slots is of paramount importance. A mis fit washer on an alloy frame will crack the frame when you tighten the nut. So get that right first and foremost.

Tests showed that the nut pressure is sufficient to control the torque when the number is that small.

However, if your nut loosens then you are pooched. Even steel bikes can benefit from a torque arm backing up the nut.

Some bikes are easier to fit a torque arm to than others, but I'd say get one torque arm anyway.

 

[3wheels1life]

Thanks everyone who replied.

What type of torque arm should I use (the wires on my motor come out the end of the axle)?
Can you post (a) link(s) to good torque arms?

Thank you so much, your advice is much appreciated!

-3wheels1life

 

[cal3thousand]

Thanks everyone who replied.

What type of torque arm should I use (the wires on my motor come out the end of the axle)?
Can you post (a) link(s) to good torque arms?

Thank you so much, your advice is much appreciated!

-3wheels1life

A member on here makes very good torque arms: Migueralliart

 

[jbalat]

This is the one I made for my crystalite 5404 motor.
6mm mild steel plate. 3 days work drilling and filing.. I actually made the slot a little too big but managed to squeeze in a 0.010 feeler in the slot, folded it over and popped on the washer and nut to keep it secure. So no slop. Then I installed the torque arm under the frame so I can match drill the mounting holes. Finished with a coat of paint I think it looks ok ?