File these silly angles off my dropout? How risky is it lol

[Manc44]

Part of my bike frame near the dropout has these angled ridges that will overlap part of the torque arm that goes on the axle.

What risk is there in filing those ends of the ridges flat so the torque arm plate sits flat?

On this image, I have taken away the 2 parts of the torque arm plate so you can see where the ridges of the frame gets in the way of it...

Filing the torque arm isn't an option because I'd be filing so much into it, it would be too weak - I'd be filing it nearly all the way across it.

I have seen adjustable torque arms with that little 18-point star and while that's really clever, each point is 20° of adjustment (18 points /360° = 20°) and I think the offset on my frame is about 24° so, there's just not enough points on that star thing to do it (maybe if it has a gazillion points or rather, 360° /6° = 60 points, then I'd just move it around 4 notches to get that 24° offset I need.

Then there's a more expensive torque arm called "Arc", thats about £30 that does have 32 points, but even then 360° /32 = 11.25° per point and I fear that one still might not have the adjustability required, so, frame filing seems about the only option (or get a mid-drive HAHA - that was nervous laughter by the way).

For reference here it is without the torque arm covering stuff up, the ridges almost end up where the standard quick release is, sigh...

 

[vfr400]

Why don't you flip it so that it's clear of the frame?

 

[Manc44]

Why don't you flip it so that it's clear of the frame?

Thanks vfr400 but I have already tried that - the end of the slot in the long piece won't reach the hole on the short piece, if the short piece is flipped vertically.

You can probably see where the hole in the short piece will end up if I do that - about 3cm lower - while the longer piece has to stay where it is due to the hole at the top being held by the caliper bolt.

What I've not tried is abandoning the caliper bolt idea and instead, flipping the short piece, then putting the long piece so the force is going against the chainstay. If this is what you already meant, my apologies.

With only an M6 bolt and smooth washers holding it, I think I need to get a custom one made that's all 1 piece.

 

[vfr400]

Thanks vfr400 but I have already tried that - the end of the slot in the long piece won't reach the hole on the short piece, if the short piece is flipped vertically.

You can probably see where the hole in the short piece will end up if I do that - about 3cm lower - while the longer piece has to stay where it is due to the hole at the top being held by the caliper bolt.

What I've not tried is abandoning the caliper bolt idea and instead, flipping the short piece, then putting the long piece so the force is going against the chainstay. If this is what you already meant, my apologies.

With only an M6 bolt and smooth washers holding it, I think I need to get a custom one made that's all 1 piece.

Make your own tie bar out of a bit of scrap steel strip. All you need is a piece with a hole in each end. I nearly always make my own rather than use the ones that come with the torque arm. The steel doesn't have to be anything special. It's only the piece that goes on the axle that has to be strong.

 

[Peddlin' Pedro]

Wouldn't recommend it. Your dropouts are cast pieces, with those ridges amounting to a collection of connected triangles for strength and rigidity. You might get away with it, or you may find that after a few good hits you see cracks starting at the point you've filed into as the loads no longer dissipate out towards the points.

 

[Manc44]

I finally got it fitted There's no hub motor in sight yet, but this is at least proof of concept for now, without having to file those ridges I mentioned. In reality the axle slot in the torque arm lined up and it rests flat, without interfering with the ridges.

I did have to slightly file the bottom corner of my dropout, right on the tip, to get a gap between the washer/bolt of the torque arm.

The finished product - if the hub motor axle does slip, it doesn't have far to go before it should lock up (the small distance in the slot on the lower part of the long torque arm piece)...

A 3mm thick washer had to be used against the frame, at the caliper bolt, to make the torque arm flush with itself. The reason there's also one under the bolt head is, I couldn't get a 27mm bolt and didn't want to risk hacksawing the only bolt I had, so I used a 30mm bolt and the 3mm washer to space it. There's about 0.5mm of bolt sticking out on the inside of the disc brake adapter but it's well clear of the rotor...

The bit that got filed off, center of image...

Glad I finally got this to fit because I have been fretting for three days over it lol.