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Can Grin 311 Front Torque Arm Be Used on Rear G310 Hub.?

KitsBeach

10 mW
Joined
Sep 21, 2022
Messages
30
I'm wanting a torque arm on my bike. Even though it might not be needed, I'd feel better about it.

Can a Grin Front Torque Arm 311 Be Used on a Rear G310 Hub.?

I notice Grin shows the front 311 torque arm in their website drop-down menu options for the rear G310 kit. But, when I asked Grin, they suggested I use a V4 torque arm (but it seems to me that the G310 hub has round axles and therefore no place for the V4 torque arm to hold on and do anything).

The front 311 torque arm goes on the inside of the frame and replaces the anti-rotation washer. It seems to me that it should fit on the rear as well, especially since I have a fender eyelet right there.

Just wondering if anyone here knows first hand about this, before I buy another (incorrect) torque arm.
 
Either should work. Just depends on your frame and where the convenient anchor points are. A picture of the dropout might be helpful.
 
Torque arms aren't specific to a motor, but only to an axle size.
 
Screen Capture from https://youtu.be/qHj3Qk5Whfo
Bafang G31X Axle.png
The G31X motors do have flats on the axle shaft but they are "inboard" of the dropouts. It may be difficult to see but note the area where the yellow "X" is drawn. I can imagine one might have a conflict between the disk caliper and a torque arm if disk brakes are installed.

Edit:
The drive side appears to have flats as well:
GHw7cmm.jpg


FYI, Long thread on the G310 Motor: https://endless-sphere.com/forums/viewtopic.php?f=2&t=92124
 
Thanks for the replies..!!

I'll confirm that, yes, the G310 has inboard axle flats (and that is why V4 torque arm is not appropriate).

Here are pictures of my rear dropouts.

I'm pretty sure the 311 front torque arm would work (which is why they offer it as an option on their kits). The person I was talking to at Grin may not have known exactly what I was talking about.

Please take a look at these photos and let me know what you think.

Rear dropout right-2.JPG

Rear dropout left-1.JPG

Edit: the V4 torque arm is appropriate it just needs to be mounted on the inside of the frame.
 
I'll also say its probably a bit crowded on the right side of my bike, maybe could use torque arm on the left.
 
LewTwo said:
I can imagine one might have a conflict between the disk caliper and a torque arm if disk brakes are installed.

Thank you for this LewTwo.! Good thing for me to check.!

Here are some pics from bottom left side, and I think there is room for a torque arm.

Left side drop outs from bottom -2.JPG

Left side drop outs from bottom -1.JPG
 
KitsBeach said:
I'll confirm that, yes, the G310 has inboard axle flats (and that is why V4 torque arm is not appropriate).

I can't tell from the images; is it just not possible to install the V4 inboard of the dropout on your frame/wheel/etc setup? It has a lot of possible angles it can mount in, especially since your motor axle can be rotated in any orientation as the axle itself in the dropout area is round. I think, but can't see for certain, that you could use just the axle-mounted portion of the arm, and clamp it directly to your frame, rather than using the bolt-on portion, and this could simplify your installation and make for less points of failure depending on how the arm fits against the frame. (may even be possible to file the arm to fit the curve of the frame tubing for a really close fit)
TorqArm_V4[1].jpg


If it won't, then any torque arm that fits as snugly as possible on the flatted axle segment you do have, and will fit between the frame and wheel without interfering with moving parts, etc., would be appropriate.

If you can't tell, you could take some plastic (in layers if necessary) or even cardboard, and cut it out according to the best info available about any particular torque arm you want to try, then see if it fits where you need it to without distorting it.

If it does require changing it's shape, then that's also ok as long as you have the necessary tools to do that to the actual torque arm as well. :)

The primary requirement for a good torque arm is that it fit the flatted axle section of the motor as snugly as possible in all dimensions, and that it use as much of the flatted section as possible to contact the flatted faces of the torque arm itself, for maximum torque transfer into the arm.

The looser the fit, or the lower the mating surface area, the less torque transfer there is via the arm, and the more likely a failure of the interface is, leading to axle spinout, wire damage, etc.
 
KitsBeach said:
I'll also say its probably a bit crowded on the right side of my bike, maybe could use torque arm on the left.
Well for 20 Bucks, I would say it is worth a try.

https://ebikes.ca/torqarm-311.html
https://ebikes.ca/amfile/file/download/file/142/product/950/
 
amberwolf said:
I can't tell from the images; is it just not possible to install the V4 inboard of the dropout on your frame/wheel/etc setup?

The other thing one can not tell from the images is if the hole is the same size for both the G311 and the V4.
Personally, I do not like loose fitting torque arms.
 
Well, AFAIK the Grin arms will have a hole that has 10mm between the flats. (how exact, I don't know, but i expect its' a lot better than the average torque arm out there...how close a fit it is on any particular axle will also depend on the axle's tolerances, some of which can be pretty wide).

The motor itself in this case says it's 3/8" round axle, which is a bit smaller than 10mm, and the flats in the image of the axle do appear to be just that slight amount more than 3/8" that 10mm is, so my best guess is that they are also 10mm.


The other dimension, parallel to the flats thru the axle, from rounded endpoint to rounded endpoint, is probably 12mm. The Grin v4 arm is a 14mm long hole, so it would fit, but it leaves a mm of open space at each end if centered (or up to 2mm on one end if not). It's still better than many torque arms I've seen. :)

Thickness...seems to be about the same for both. If the Grin arm is too thick, and would cause interference with the rotating part of the motor for some reason, it could be filed or sanded without significantly affecting it's ability to withstand the torque.


Can't tell for sure without actually fitting it on there....but worth a shot. :)
 
Totally worth a shot..!!

Don't know why I didn't think of this but I'm glad I asked the right people.!

The Grin V4 torque arm is just slightly larger than 10mm between the flats btw. I can't remember the exact measurement but I did measure it and thought "close enough".

The anti-rotation washer is actually pretty thick between the frame and the hub, so I feel hopeful about this. I can always widen the frame a little bit more.

Edit: I measured the V4 torque arm and it seems to be 10.25mm between the flats
 
KitsBeach said:
Totally worth a shot..!!

Don't know why I didn't think of this but I'm glad I asked the right people.!

The Grin V4 torque arm is just slightly larger than 10mm between the flats btw. I can't remember the exact measurement but I did measure it and thought "close enough".

The anti-rotation washer is actually pretty thick between the frame and the hub, so I feel hopeful about this. I can always widen the frame a little bit more.

The nice thing about having the round axle in the dropout is that you can rotate the axle flat, so aren't stuck with the typical angles compared to having a fixed orientation of other hub motor axles. If by some miracle the distance between the axle centerline and the fender eyelet is the same as the V2, you could use an extra long fender bolt, assuming the eyelet has a through hole, and use that to secure the torque arm with a nut.
 
KitsBeach said:
I can always widen the frame a little bit more.

For those of you thinking that widening the frame is going to mess with the disc calliper spacing, well...you are right.

So I spaced it a bit with a couple m6 washers.

Shimmed caliper mount-1.JPG

Shimmed caliper mount-2.JPG
 
Thanks for everybody's help with this.

I cut off the extra bit of the hose clamps and wrapped them with this self-sealing silicone tape.

wrap-it self-sealing silicone tape.JPG

De-edged hose clamps-1.JPG

De-edged hose clamps-2.JPG

V4 torque arm on bottom chainstay-3.JPG
 
Here is a comparison of the thickness of the V4 torque arm to the bafang anti-rotation washer.

comparison thickness of torque arm to anti-rotation washer.JPG

bafang anti rotation washer.JPG
 
And here is a couple pics of alternate locations for the torque arm that didn't work for me because it either hit the caliper or interfered with bump in my frame.

Alternative torque arm fittings-5.JPG

Alternative torque arm fittings-4.JPG

Alternative torque arm fittings-3.JPG

The bike is upside down in all of these pics btw....

There was a suggestion that I could rotate the torque arm wherever I liked it but I wanted to keep my anti-rotation washer on the other side, so I ended up on the lower chainstay. I don't think the torque arm would have fit anywhere else on my frame anyway.
 
Glad it worked out easily enough. :)

How much rocking happens with teh axle flats in the torque arm because of the oversized spacing?

It shouldn't matter much becuase I don't think you can't use regen with that motor (internal freewheel/clutch), and regen causing rocking back and forth repeatedly is what more often than not defeats torque arms, etc.

If there's enough torque it could cause a problem, but if the antirotation washer never had a problem (those are generally kinda loose in the ones I've directly worked on in other Bafangs), and never caused a problem with the dropout, the torque arm will probably be fine, too.


FWIW, I think with the frame design you have, if it could fit there, I would probably have pointed the arm (without the extension) "forward and up" between the chain and seat stays, along the dropout flat. If the meat of the dropout plate lined up with enough of the mounting slot in the dropout, I would then use the bolt intended to hold the extension to the arm to bolt it directly to the dropout plate instead, drilling a hole for it in the plate whereever it lined up. (assuming that bolt head would clear everything on the motor on the inboard side of the arm).
 
amberwolf said:
How much rocking happens with teh axle flats in the torque arm because of the oversized spacing?

I don't think it rocks at all, but it is hard to tell. Its not a big motor and the rear dropouts are pretty robust. But, yes, I wanted a torque arm in the mix.
 
amberwolf said:
FWIW, I think with the frame design you have, if it could fit there, I would probably have pointed the arm (without the extension) "forward and up" between the chain and seat stays, along the dropout flat.

That's a good idea I will go look at it and ponder that. I think my disc caliper might be in the way tho (if that's what you mean by "forward and up").
 
KitsBeach said:
amberwolf said:
FWIW, I think with the frame design you have, if it could fit there, I would probably have pointed the arm (without the extension) "forward and up" between the chain and seat stays, along the dropout flat.

That's a good idea I will go look at it and ponder that. I think my disc caliper might be in the way tho (if that's what you mean by "forward and up").

Ahh ok amberwolf, I see what you are saying. It might fit into the "forward and up" location. It is a little tight and I'm not sure if the flats would let me choose that location, if I want to keep the anti-rotation washer on the drive side.

Here's a couple pics of that spot, in case anyone else is thinking about this.

Potential forward and up torque arm location -3.JPG

Potential forward and up torque arm location -2.JPG

Potential forward and up torque arm location -1.JPG
 
And a couple right-side-up pics of my final install. Its a bit easier to understand when the bike is right-side-up.

Right side up pics of V4 installed-3.JPG

Right side up pics of V4 installed-2.JPG

Right side up pics of V4 installed-1.JPG
 
I've only ridden this motor 9 kilometres, all without a torque arm. So it is hard to tell if there is any rocking. I don't think so. Addition of the torque arm should improve things even more.
 
Looks well done to me. :thumb: :thumb: :thumb:
For posterity and future reference, the next time that you pull that motor off please measure and post the distance across the flats, diameter and thickness of that section of the axle.
 
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