Torque bar needed on aluminium offroad bike?

[Marsbar]

I am waiting for the Magic Pie 4, my 2nd build.

This time I ordered a rear motor. I have an aluminum frame bike. I want to set the motor on max. 20A 48V. This is important in order not to stress the batteries too much.

Now the question is, if you install it in front you need a torque bar because of only two tiny lips holding the weel.

Can I skip the torque bar this time since I am installing in rear where there are more solid aluminum around the bolt, and I have limited the torque to 20A power.

Would save me allot of work since I have to cut a torque bar from 4mm stainless steel plate.

Any recommendations? Should I take a picture?

Bicycle is a 28 inch weel offroad with installed front damper.

[Bikemad]

Can I skip the torque bar this time since I am installing in rear where there are more solid aluminum around the bolt, and I have limited the torque to 20A power.

250 watts or less should be fine in nearly any steel or aluminum dropout without torque arms. 500 watts is about the limit you’d want to put in rear aluminum dropouts without a torque arm. If you have a 500 watt motor in the front, especially if you have an aluminum fork, you’ll want to use a torque arm. 750 watts or above should almost always use a torque arm, even in the rear of the bike, even in steel. Generally speaking, 750 watts in rear steel dropouts will probably be fine, but it’s getting near the limit. That’s why we recommend 750 watts or above, using a torque arm.

20 Amps may not seem a lot, but with a fully charged 48V battery it is still going to be over 1000 Watts of power, and that amount of power will produce a large amount of torque, especially with the MP4.

I would not want to use an MP4 in an alloy frame without some form of torque arm, but as it's your motor, your bike and your safety being put at risk, the final decision is yours too.

Check out Justin's superb article on torque arms for further information

Alan