Can someone double check my torque arm installation?

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transposon   10 W

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Can someone double check my torque arm installation?

Post by transposon » Nov 15 2019 1:07pm

This is my first build and I was wondering if someone could let me know if this was installed correctly.
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torque arm.png
torque arm.png (285.72 KiB) Viewed 1298 times
Last edited by transposon on Nov 15 2019 5:41pm, edited 1 time in total.

Balmorhea   100 W

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Re: Can someone double check my torque arm installation?

Post by Balmorhea » Nov 15 2019 2:48pm

That link doesn't work right. Take off the IMG brackets so it will show as a hyperlink.

Anyway, it looks OK to me, as long as everything is nice and tight. What's the maximum torque of your motor?

transposon   10 W

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Re: Can someone double check my torque arm installation?

Post by transposon » Nov 15 2019 5:42pm

Thanks for the heads up, I attached a pic directly.
I am using a 1000W ebay hub motor with a 14s battery on a Trek 4500 aluminum frame. I probably will stay at 25mph or less.

It is a grintec v4 torque arm. I tried installing another on the opposite side, but the arm hits the bolt that holds on the disc brakes. I may try and find a different torque arm for the other side if it is necessary.

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E-HP   100 kW

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Re: Can someone double check my torque arm installation?

Post by E-HP » Nov 15 2019 6:10pm

transposon wrote: It is a grintec v4 torque arm. I tried installing another on the opposite side, but the arm hits the bolt that holds on the disc brakes. I may try and find a different torque arm for the other side if it is necessary.
Can you post a pic of the problem side and how the torque arm interferes with the caliper bolts?

There may be a way to fabricate something. For mine, I bolted on a plate with longer caliper bolts, then drilled and tapped the plate to fix the torque arm to:
viewtopic.php?f=6&t=97945#p1451659

I have a cheap generic one on the other side, mainly set up to handle regen.

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dogman dan   100 GW

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Re: Can someone double check my torque arm installation?

Post by dogman dan » Nov 16 2019 8:02am

Picture looks correct to me.

markz   100 GW

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Re: Can someone double check my torque arm installation?

Post by markz » Nov 16 2019 7:16pm

You could try reversing the torque arm on the problem side and see how it fits.

transposon   10 W

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Re: Can someone double check my torque arm installation?

Post by transposon » Nov 16 2019 10:04pm

Here is a pic of the other side. The bolt that holds the brake calipers keeps the torque arm about 1/2" from the drop out.
torque arm 1.png
torque arm 1.png (484.89 KiB) Viewed 1187 times
torque arm 2.png
torque arm 2.png (451.15 KiB) Viewed 1187 times



Here is a possible alternative placement, but it still has the same problem with the arm being 1/2" away from the drop out.
torque arm 3.png
torque arm 3.png (464.11 KiB) Viewed 1187 times
torque arm 4.png
torque arm 4.png (449.71 KiB) Viewed 1187 times

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E-HP   100 kW

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Re: Can someone double check my torque arm installation?

Post by E-HP » Nov 16 2019 10:16pm

try rotating it 180 degrees

EDIT: looks like it just clears the frame (actually might be nice if it touches and supported by it). If it doesn't, it can be flipped and definitely clear it.
torque arm 180.jpg
torque arm 180.jpg (57.22 KiB) Viewed 1054 times
Last edited by E-HP on Nov 17 2019 11:26am, edited 1 time in total.

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dogman dan   100 GW

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Re: Can someone double check my torque arm installation?

Post by dogman dan » Nov 17 2019 7:24am

yup. point it down.

transposon   10 W

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Re: Can someone double check my torque arm installation?

Post by transposon » Nov 17 2019 1:58pm

torque arm 5.png
torque arm 5.png (391.75 KiB) Viewed 1037 times


I thought about that, but given the direction of wheel rotation and the fact that the arm would be held on by hose clamps, wouldn't it not do much to resist the axle rotating? It seems to me that the outer arm would just slide down the frame.

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E-HP   100 kW

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Re: Can someone double check my torque arm installation?

Post by E-HP » Nov 17 2019 2:11pm

transposon wrote:
Nov 17 2019 1:58pm
I thought about that, but given the direction of wheel rotation and the fact that the arm would be held on by hose clamps, wouldn't it not do much to resist the axle rotating? It seems to me that the outer arm would just slide down the frame.
To me it looks about as good as it gets.

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NCC1941   10 mW

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Re: Can someone double check my torque arm installation?

Post by NCC1941 » Nov 17 2019 3:00pm

transposon wrote:
Nov 17 2019 1:58pm
I thought about that, but given the direction of wheel rotation and the fact that the arm would be held on by hose clamps, wouldn't it not do much to resist the axle rotating? It seems to me that the outer arm would just slide down the frame.
I've used that torque arm in that configuration on a few bikes over the last few years. It's never been a problem, even on a build where I was running 1800w peaks + some light regen. Just make sure to tighten everything down properly and it should be fine.
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transposon   10 W

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Re: Can someone double check my torque arm installation?

Post by transposon » Nov 17 2019 3:14pm

Alright, thanks for all of the input everyone. I will go with this configuration.

Voltron   10 MW

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Re: Can someone double check my torque arm installation?

Post by Voltron » Nov 18 2019 11:35am

They'll all work, but if I could make it happen easy enough, I would ditch the second part of the arm, and try to find a place where it lines up with a bolt hole in the frame already (even if it means a little hammer therapy, the steel arm can take some pre deformation without failing), or drill one in the middle of the dropout casting somewhere. It makes so many less parts to deal with.
Sometimes spacer-ing it out from the frame gets more important, as those other parts soak up some misalignment.

Voltron   10 MW

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Re: Can someone double check my torque arm installation?

Post by Voltron » Nov 18 2019 11:49am

I'd even consider sawing off the slotted section, and drilling a hole in the plate that's left... It really doesn't need that long of a lever arm when it's bolted to the frame, and with the 3d cast dropouts you have, you might even be able to cut it right to nestle in there nice and flat everywhere. The important thing is the axle slot fitting tight, the rest can be a little rough around the edges if you know what I mean...

Voltron   10 MW

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Re: Can someone double check my torque arm installation?

Post by Voltron » Nov 18 2019 11:59am

On a different note, is that as far as the axle goes into the dropouts? Usually you have to file a bit off the frame to get a hub motor axle up in there far enough, which you would want to do before going crazy on the perfect torque arm, as it might move the holes needed. Besides trying to pry open the dropout more, it makes the brake rotor ride low, so the pads don't grab as much, and they get a lip above where the rotor is now that makes them wear fast when the pads start touching in the middle over the rotor.

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