I'd like to mount caliper rim-brakes on a rear fork where no center hole exists for that purpose. I'm trying to find the part underlined and shown in white on picture attached.
enter image description here

As you can see these rear Shimano calipers are fixed to this U- or horseshoe-shaped part that itself was tightened using the holes where normally 2 v-brakes are fixed.

I'm only trying to find this part online, but have no idea what it is called (whether in French or English or whatever...). Can someone please point me to the right direction ??


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    Does this answer your question? Mounting caliper brakes without center hole
    – GageMartin
    Commented Sep 25, 2020 at 15:25
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    I've never seen anything like that. I tried searching but couldn't come up with anything. Do you have the whole picture that shows the full URL that's cut off there? Commented Sep 25, 2020 at 16:55
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    Since post placement isn't standardized it's not too surprising all examples of such a thing appear to be original equipment to the frame?
    – Affe
    Commented Sep 25, 2020 at 19:34
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    Don't use one of these. It will flex like mad and perform terribly. Commented Sep 25, 2020 at 22:50
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    i'm sure you're aware of this but just in case - keep in mind you will need new brake levers, or cable-pull converters. Commented Sep 25, 2020 at 23:24

1 Answer 1


Note these are not product recommendations, these are examples showing the features you would need on a part to do this task. I can't find one item with all the suggested features, so you may be up for modifying existing items, or making one from scratch.

Also note that most/all of these will make wheel swaps harder in that you probably can't fit an inflated tyre into the frame.

There were items in the past called Brake Boosters, that worked with Cantilever or U brakes to support the end of the mounting posts and to stop outward flex.


Problem here is they're only bolted to the end of the boss by one bolt, whereas for braking performance you would want the two ends of the booster to go over the mounting posts, just like a V/canti brake arm.

So you need much thicker metal too - a lot of what I could find was stamped steel or aluminium, which would have too much flex for a brake. These seem to be from the BMX crowd, perhaps replacing U brakes. Contrast with this casting that is easily three-times thicker, and has a top hole intended for a caliper brake bolt:

enter image description here
from http://ratrodbikes.com/forum/index.php?threads/rim-brake-adapter-for-fat-tire-bike.94912/

Here's another similar one from the side, but this one clamps around the fork's tines/seat stays, and does not use any bosses. Since you have bosses it would be best to use them.

enter image description here
from http://buildesign.co.jp/kimori/front-brake-adapter/

enter image description here
from http://buildesign.co.jp/kimori/rear-brake-adapter/ (dead) https://web.archive.org/web/20170117014042/http://buildesign.co.jp/kimori/rear-brake-adapter/

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    I had seen these "boosters" too, to reinforce cantilever brakes - but that's not the same... All I got from maker is that this is a "CNC part" that shouldn't be too difficult to find anywhere... No idea what "CNC" stands for, and in spite of all search terms I used I wasn't able to find this horseshoe stuff...
    – Seb
    Commented Sep 26, 2020 at 8:45
  • @Seb yes that's the point - there are brake boosters which might look like they will work, but they wont. You want something cast not stamped, and that goes over the existing brake bosses, not just bolted to the end. You may have to make it yourself from a thick chunk of aluminium or get a job-shop machinist to make you one from a plan.
    – Criggie
    Commented Sep 26, 2020 at 8:52

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