Torque arms for rear wheel drives - are they really necessary?

[krzychoniusz]

Hi everyone,

As in the subject line, do you think torque arms are required for conversion kits up to 1500W if DD hub motor is mounted on the rear wheel? I have read a lot of stories where front forks snapped under much stress but did not find much evidence to suggest rear frame bars can't handle this much power. Does anyone have any experience in this subject and could clarify whether this is just a good practice and a preventive measure or a real requirement for the rear wheel drives?

Many thanks

K

 

[Woosh]

yes.
Any unprung weight greater than 4kgs at the rear wheel should really have a torque arm. It's not just for the torque, when your bike hits a pothole, the inertia can pull the wheel off the frame or round the dropout openings.

 

[krzychoniusz]

Thanks Woosh - that's indeed a very good reason to install a torque arm.

 

[Nealh]

The other good reason is you won't need to buy a new hub when you ******* up the motor cable when it rotates in the axle.

 

[krzychoniusz]

So the question is, is single torque arm enough or should you install one on each side of the wheel?

 

[Woosh]

you should fit two, one on each side.

 

[Nealh]

I only fit one on the brake side amking sure my AR washers are fitted never had an issue with 3 hubs 350 - 500w power.

 

[John L]

I only fit one on the brake side amking sure my AR washers are fitted never had an issue with 3 hubs 350 - 500w power.

Interesting. It would make it that bit easier to remove the wheel.

Sent from my SM-G950F using Tapatalk

 

[Nealh]

If possible try and make you own torque arm, it can then be the shape you want to blend in better. A one piece arm is what I make no joint to move, the important bit is to make sure axle hole shape is snug and tight then only requires affixing to the rear end. Often you can use an existing tapped hole.

 

[anon4]

If your bike has the anti rotation washers and it's not stupidly high power you'll be fine without. Front wheel is a different matter

 

[krzychoniusz]

Depends what you mean by stupidly high power? My original post mentioned 1500W DD hub motor, I guess for that torque arms are a must?

 

[Woosh]

it's best to err on the side of caution.
put that wheel on the scales.
If it's more than 5kgs, you'll need both torque arms.