Torque arms

roostersgt

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Could someone post up a few pics of the proper placement of where torque arms should be mounted on both a rear hub drive and front hub drive? I’m building both and have seen conflicting information. On the rear it seems the arm should be mounted below the chain stays, and on the front , behind the fork, not in front. Is this correct? Thank you.
 
Could someone post up a few pics of the proper placement of where torque arms should be mounted on both a rear hub drive and front hub drive? I’m building both and have seen conflicting information. On the rear it seems the arm should be mounted below the chain stays, and on the front , behind the fork, not in front. Is this correct? Thank you.

My take is you want the arm, if it tries to rotate, to place its load onto the frame, not onto the weaker retaining band/s e.g. hose clamps being popular. What ever side and position puts that potential axle rotation (opposite to the forward wheel rotation) against the frame is the right place.
 
On the rear it seems the arm should be mounted below the chain stays, and on the front , behind the fork, not in front. Is this correct? Thank you.
Short answer is yes, if you are putting the arms on the non drive side.

Grin technologies torque arms are going to be more expensive but also of MUCH higher quality. Also, Grin has an excellent info page on how torque arms work which also answer your placement question. Note the 'V1' arm they show is widely copied and is junk relative to what else is out there in the world in 2023.


One thing I have done on front motors is to always use two torque arms. One on each side and despite the fact that one of them can be argued to be on the wrong side, the fact that two are in place just plain locks the motor down in the dropouts whether it likes it or not. The two together are enough to counteract anything a 2 kw motor can throw at them. Just checked my build pics and the first set I did have been in place since 2018 on a chromoly fork.

Here's a rear one. Ignore the slight space above the bolt on this one. I actually slotted the arm a bit so the M8 sliding dropout bolt could fit thru it. Its not possible for it to slip. this is another 2kw peak motor (58.8v x 35a = 2058w). If you are using a more powerful motor than this you want to be upping your game beyond what I am doing here.

IMG_20181008_113107.jpg
 
Short answer is yes, if you are putting the arms on the non drive side.

Grin technologies torque arms are going to be more expensive but also of MUCH higher quality. Also, Grin has an excellent info page on how torque arms work which also answer your placement question. Note the 'V1' arm they show is widely copied and is junk relative to what else is out there in the world in 2023.


One thing I have done on front motors is to always use two torque arms. One on each side and despite the fact that one of them can be argued to be on the wrong side, the fact that two are in place just plain locks the motor down in the dropouts whether it likes it or not. The two together are enough to counteract anything a 2 kw motor can throw at them. Just checked my build pics and the first set I did have been in place since 2018 on a chromoly fork.

Here's a rear one. Ignore the slight space above the bolt on this one. I actually slotted the arm a bit so the M8 sliding dropout bolt could fit thru it. Its not possible for it to slip. this is another 2kw peak motor (58.8v x 35a = 2058w). If you are using a more powerful motor than this you want to be upping your game beyond what I am doing here.

View attachment 8812
Do you have pictures of front both sides?
 
Do you have pictures of front both sides?
No, but they look the same on both sides. Here's a shot from my first ride post-build back in 2018. This was cleaned up a little afterwards, but it stayed essentially the same setup with some changes to the washers I used. At bottom is a different method on a different bike that works of course only on the non drive side since it uses the brake adapter bolt.

In the top pic, if you notice the modified brake mount, this is a Surly Ice Cream Truck fork and they use rear brake spacing. So to use a standard front hub I had to measure and in this case hand-file a modified brake mount.

This is a standard-issue Grin v2 torque arm that uses the dropout eyelet. Because the two are so close together, there is slack in the connecting arm. I eliminated the possibility of slippage by putting a second bolt in place as a sort of 'earring' underneath the one that connects to the actual torque arm. My revision after the fact was to go for smaller washers and putting that earring up high so its in direct contact with the connecting bolt. Notice also I used a spacer directly adjacent to the dropout, and underneath the connecting arm. This puts the connecting arm on the outside of the torque arm, and not onto the inside. The idea was that allows me to set those bolts directly adjacent to one another.

Different bikes will always have different spacing so you should always be prepared to wing it with regard to how you set up a torque arm. In particular its never a bad idea to lay in a few extra torque arms of slightly different designs so you can mix and match parts. That will be what you see in the pic down below this one.

This is an 80 Nm motor with a 35 amp controller so it gets very strong motor power. I have about 7000 miles on this bike as of today and no shifting and no markings inside the dropout from the axle digging in (i.e. it works perfectly as shown). Again, I did this same thing on both sides. Only one torque arm is needed for a motor with these specs, so the second one on the other side is only going to further lock the axle down, not cause some kind of condition where it wants to jump out of the dropout.

IMG_20181007_165742.jpg


And here's another way to do the non-drive side. This was a different bike in 2017. I took a similar Grin v2-style stainless torque arm, and instead of using the short dropout connecting arm, used a long one that let me do a full-extension clamp that needs nothing extra to fully immobilize the axle. (I still put another eyelet style arm on the other side). This was a bike where I physically destroyed my fork by using a Grin v1-style hose-clamp-restraining torque arm on and learned first hand why Grin and the rest of the experienced DIY community says they are crap by modern standards. I really wish I kept the pics of my spread steel dropouts on the fork that was permanently destroyed by me cheaping out and using a $10 clone torque arm.

20170412_184515.jpg



And since the rear shot I put out earlier for the orange bike is specific to a sliding dropout where there is no brake bolt to work with, here's another way to do a rear arm where you have a brake bolt available to work with. Here again you can see the on-the-fly nature of fitting a torque arm, as this bike used a front connecting arm, an entirely different torque arm upside down and backwards, and spacers and washers all over the place to get fitment just right. This particular setup lasted about 4000 miles until I cracked that frame (thanks to a dumb thing I did with the rack boss on the other side. Not related to the torque arm).

20170412_184604.jpg
 
On the rear it seems the arm should be mounted below the chain stays, and on the front , behind the fork, not in front. Is this correct? Thank you.
Worth noting: If you are doing a direct-drive motor with regen, then two torque arms both behind a fork or under a stay are actually correct. Regen puts pressure on the axle in the opposite direction as it would under acceleration, so you want a torque arm that does the opposite job.

Just as I am doing what I am doing knowing I am well under the limits that would cause any sort of problem, and which end up being beneficial with my parts and power level, you have to be up pretty high on the food chain to need a torque arm dedicated to counteracting the stresses of regen. As in a big motor where you have dialed up the regen effect.

Probably not something a new builder is going to encounter, but worth mentioning. Also the Grin Tech article I linked earlier in this thread gets into this regen subject as well as the two torque arms thing so a careful reading of that article and the faq at the bottom is not a bad idea.
 
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