Dropouts, Grin v4 Torque Arm doesn't fit

[majornelson]

My great thanks to all on this forum. I've been browsing (pouring over the details) for a couple of months and finally completed my first build. It is a Trek DS 8.4 with an aluminum frame. I built it out using a MAC motor and 48v frame battery from cell_man (em3ev.com) with cycle analyst v3. Nice setup (although I struggled with the disc brake...)!

I purchased a Grin Technologies torque arm v4 but it won't fit with my rear rack and dropouts...

So...

1) How much risk to a commuter bike do I have without using a torque arm on the rear with this motor?
2) Any alternative (for purchase) torque arms recommended?

Attached is a photo of the (in progress) build. I couldn't have done it without the great information on this forum.

Lee

 

[biohazardman]

I am sure that the Mac motor will have enough torque to twist in your dropout sooner or later. How long I can't say with everything good and tight you may be able to get by for some time depending on your riding habits. Still I would put a torque arm on right away to be sure I would not have a malfunction that might cause me injury. Can you show us pics as to why it won't fit?

 

[mark5]

The left side dropout looks pretty clear on one not so clear Internet closeup picture of a Trek 8.4 DS. Granted, the motor wire comes out on that side but the wires can be removed from their plug shells and threaded through the torque arm. Majornelson, you're sure you can't use the left dropout?

 

[majornelson]

I'll post pics today. And I'll double check the left side again (most of my efforts were on the right side). I have a rear rack that is complicating things.

Thanks!

 

[dogman dan]

What's cheaper to replace? One rack? Or one controller, one motor, and one frame? Not even counting potential medical costs.

That clear enough? You need the torque arms, properly fitted, much much more. Sort that, then solve the rack problem.

 

[melodious]

I'd ride it, but don't overdo the WOT stuff at complete stops. BUT, knowing full well that eventually I won't fall into the "oh it's fine as is" mode, eventually getting a torque arm that fits. I'm sitting here contemplating a similar motor/battery build. 8)

 

[RLD70]

Take it from experience, you dont want to be riding along then all of a sudden your motor drops out of the dropouts. It can be both painful and an expensive repair that couldve been avoided by using a TA or 2.

 

[MadRhino]

Making your own custom torque plates is not so complicated, and takes little time compared to all the hassle of a dropout failure.

 

[melodious]

Are you suggesting he just glue/epoxy on a wrench? Har har! Ghetto! I love it. 8)

 

[majornelson]

Got it! I was able to fit the torque arm on the left (non freewheel) side... Re-worked and shimmed the rack. Really wasn't much so I'm not certain why I didn't try it earlier.

I really appreciate all of the feedback. I've attached a photo of the setup. Please let me know if I missed anything.

Best.

 

[MadRhino]

It will do for low power, but it is weak and couldn't stand real torque or regen.
You had room there to make neat and solid torque plates