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Brake stay/torque arm that will clear wide tire

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Brake stay/torque arm that will clear wide tire

PostAuthor: briandk » Wed Oct 09, 2019 8:35 am

Swapping my rear tire, I mostly focused on chain clearance and kind of forgot about the brake stay / torque arm that prevents the brake drum plate from spinning.

This thing:
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I'm running a 170/60 17" rear tire and I need about 1-2 cm extra to clear the wheel. I've tried to see if I could do it with spacers and I can gain a few millimeters on the point where it anchors to the brake plate, but on the frame the mount point is a crevice which makes it hard to do right. Instead I've been considering fabricating a new bar with bends in it like this:

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If I make this from 3-4mm thick and about 25mm wide steel, how likely is it that this will stretch/break under stress when braking and kill me?

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Re: Brake stay/torque arm that will clear wide tire

PostAuthor: bstig60 » Wed Oct 09, 2019 10:03 am

Fabricating a new torque arm is your only choice. Curious where the 17 inch rim came from>
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Re: Brake stay/torque arm that will clear wide tire

PostAuthor: briandk » Wed Oct 09, 2019 10:23 am

bstig60 wrote:Fabricating a new torque arm is your only choice. Curious where the 17 inch rim came from>


It's a chain driven bike (TR1), so I'm running a Honda CB750 hub with a wider rim laced onto it. There are some details about it here: viewtopic.php?f=12&t=58098&sid=9ec80cd04620219dd133453b729f2ed1#p477250

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Re: Brake stay/torque arm that will clear wide tire

PostAuthor: Cusstout 1100 » Wed Oct 09, 2019 11:19 pm

Tubing would be a better, more rigid, choice of materials. If I had to use flat bar, I'd likely weld in a gusset at each of the bends on the outside to stiffen it up. I'm not an expert by any means, just a couple thoughts.
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Re: Brake stay/torque arm that will clear wide tire

PostAuthor: Flyingdog » Thu Oct 10, 2019 3:04 am

:yup:

Was thinking close to same thing. But was wondering if one could cut off and weld in new clevis type thing with a fairly thick walled steel sleeve on the front end. Sleeve (w/harden bolt) long enough to clear tire, then Z-bend back to brake plate, once you clear the tire. There, you could gusset the inside of the Z-bend. This way you'd only have one bend. I would think, since the torque forces would be "pull'n", they wouldn't be as stressful as if they were "push'n" on the rod/bar. And..any lateral flex would be eliminated "cuz" of this pull'n rather than push'n. :;:
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Re: Brake stay/torque arm that will clear wide tire

PostAuthor: briandk » Thu Oct 10, 2019 4:10 am

Flyingdog wrote::yup:

Was thinking close to same thing. But was wondering if one could cut off and weld in new clevis type thing with a fairly thick walled steel sleeve on the front end. Sleeve (w/harden bolt) long enough to clear tire, then Z-bend back to brake plate, once you clear the tire. There, you could gusset the inside of the Z-bend. This way you'd only have one bend. I would think, since the torque forces would be "pull'n", they wouldn't be as stressful as if they were "push'n" on the rod/bar. And..any lateral flex would be eliminated "cuz" of this pull'n rather than push'n. :;:


I'm trying to imagine the force direction in my head with a little difficulty, but won't they always be pulling and trying to stretch the bar? I like the idea of only one bend though,

I saw Cognito moto went with the Z bends on their CB550, but I don't know how much that bike is just for show vs. riding.

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I was thinking if I add some flatbar pieces cut in triangles and weld them perpendicular to the bar at the bends like this, that it might better the design

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Re: Brake stay/torque arm that will clear wide tire

PostAuthor: Cusstout 1100 » Thu Oct 10, 2019 10:49 am

Yes, "gussets".
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