Flat Mount Brakes on Post Mount Frame...Is It Even Possible?

Discuss light weight issues concerning road bikes & parts.
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by allenpg

I've been doing some searching and was curious if putting flat mount brakes on a post mount frame/fork was even mechanically possible. There don't seem to be any adapters, and I figured someone would have created one by now if it was. Thought any engineers might be able to weigh in. Thanks!


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by romanmoser


by Weenie

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by morganb

I did a lot of research on this after finding a bike that was perfect except for post mount and I wanted future compatibility with Shimano. I ended up going custom as a result. The long and short answers were both no.

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by joejack951

TRP has lead me to believe that is it mechanically possible, perhaps with some rotor size constraints. I need to take a closer look in CAD to decide for myself. If it is doable, I plan to make some. I have a post-mount disc fork on my commuter and that adapter would likely prolong its life as I get the itch to upgrade components on it.

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by Broady

It is possible but very difficult to pull off.

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by Broady


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by JAQ1

I made one like the above picture.

Used it to mount a force flat mount on my CAADX fork.

The Fork PM is for 140mm rotors. I use a 160 mm Rotor. With the mount I designed I have to space the adaptor out by 3mm to give enough clearance.

I have CAD designs for FM140 to PM140 (for 140mm rotor), FM160 to PM140(+3mm spacer needed) (for 160mm rotor), FM160 to PM160 (for160mm rotor) and FM180 to PM160 (For 180mm rotor).

My biggest problem is to get the side to side allignment correct, as a straight adaptor leaves the FM caliper too inboard. So the adaptor needs extended tabs in order to get the allignment correct.

Biggest constraint is your PM design. If its filled up too much between the posts, then there isnt enough space for the adaptor.

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by Broady

Yep, good call with the PM design, I did look into it for my Enve forks but don't think I'd have the clearance needed as they have a bit too much 'webbing' between the mounts.

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by jfranci3

You're better off paying $100 for new calipers and selling the old ones on Ebay in almost all cases.

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by MayhemSWE

Chirobike wrote: ↑
Fri Sep 21, 2018 4:51 am
Check into these.

https://www.alligatorcables.com/product ... er-04.html
Judging by the pictures those are the other way around, for attaching a post mount caliper to a flat mount frame. I'd argue they have labeled the columns in their conversion table the wrong way, though I guess that'd depend on whether you see it from the direction of the caliper or the frame…

by Weenie

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