Flat mount options for metal forks

I build gravel bikes to be compatible with road/gravel components, and that means using flat mount brakes. Recently I built my first steel fork for flat mount brakes and would like to make this the standard option for my frames, rather than a carbon fork. I’m not crazy about the front standard because of the necessary adapter and how close it is to the axle. I’m also never going to use a 140mm rotor on the front of a bike. Has anyone used or thought about using a direct mount solution for a metal fork like Open Cycle does on their carbon forks? Bad idea?


There was a bit of discussion in this thread! I’ve been considering doing the rear-style mount on my steel front fork, but need to get back into the R&D on that project. If 3D printing ended up being a viable solution, we could collaborate on something like that!

Has anyone seen any examples of this being done on metal forks? I think everyone’s concern is that the tube is weakened by the bosses, but I can’t conclude anything without any lab testing.

I find it funny that there is already a flat mount adapter standard developed for forks, but even the big companies avoid using it :rofl:

When I get some time, I will see if there is any room to engineer a custom flat mount adapter standard for metal forks.

Save yourself and your customer the heartache and splice in some xc mtb callipers! Easier to build, bigger positions, bigger pads. Nothing but wins!

For my builds if the customer wants a carbon fork, I’ll do flat mount rear but if they want a steel fork it’s IS front and rear.


Dang! Eva, I somehow missed your thread in my search. Sorry to be redundant! I’m glad there are others thinking about this. You have come up with some interesting models that prove it is a bit of a sticky subject. I look forward to seeing more and I’ll contribute to the discussion if I have any ideas.

Em, that is a practical way to go for sure. Maybe I don’t have a good enough reason to embrace the flat mount system. IS continues to prove itself a solid, versatile option - and mtb calipers are so good. Thanks for the thoughts.

@Daniel_Y this forum is really turning into something great! Totally digging the discussions on here so far.


Are you combing GRX hydro levers with XT post mount calipers? Or perhaps SRAM Hydro road to SRAM MTB calipers? Since I build for fun, and take projects that interest me (I don’t pay my bills with framebuilding) I don’t take any requests for flat mount. I’m building up a ‘gravel’ bike right now with a post mount hydro SRAM Rival groupset. It’s dumb and frustrating that flat mount is even a thing.

Yeah grx with any Shimano (or Magura) mtb callipers, and sram with (pretty much) any sram mtb calliper. The only limiting factor with sram is making sure the correct hose exists. Sram seems to have a dozen hose end standards at this point.

imo the only reason fm came around was to get brakes off the seat stays for cleaner looking road bikes. Even then I have not encountered a carbon frame brand that can consistently get the flat mount…. flat. From felt, to factor, to colnago - they all need to be sanded and filed flat by mechanics for the brake to be set up correctly.


Yes, the SRAM Hose end is very frustrating. And the hoses aren’t cheap either…

I retired from the Bike shop gig last year. Really happy I did. Last position was suspension tech. I thought framebuilding could be frustrating sometimes… doesn’t even compare to working on 4-6 different suspension brands.

At the end of it, whenever a flat mount brake came in and I had to remove the caliper for some reason I’d get some pretty bad anxiety. Had several factory built bikes where the caliper fixing bolts were fastened too tight and had deformed the metal inserts. Sanding Trek flat mounts for every single bike… never again.


It’s funny people here are talking about using the rear mount on the front while people have actually used the front mount on the rear. I have wondered if the rear is going to change, since a lot of production companies have trouble building it. Flattening the mounts on a fork should be a lot easier though. On the rear, the seat stays get in the way


Flat mount is tricky, the precision and strength needed is a pain in the ass from my experience. On the carbon forks we had made at Moots we faced every one that came through the door. If anyone is interested in having anything tested a company in California I worked with does ISO testing on frames, forks, stems etc - Engineering Materials Laboratory inc 562-945-2138. I know from conversations with Kevin at EML getting a steel fork to pass the standard required for the carbon forks is very challenging


Thanks for this input, Butch! You actually answered another question I had yet to ask, which was where to go for testing. I will have to reach out to EML as I’m experimenting with 3D printed crowns and would really like to get some lab testing done before I let a customer ride one of these forks.

Off record I would not necessarily worry about hitting the standard, just be safe and close. The limit they have is pretty extreme. There are other testing facilities as well. I can say that the testing standard is tough to hit for steel. That is why the difference between the rim brake and the disc is at least a 40% increase is weigh difference. The thing with carbon forks is they fail catastrophically not just bend. When we first started building disc road bikes the first 100 forks from a very well known carbon company had to be recalled as we had 4 of them crack and one break above the flat mount. I do consulting as well so if you want to contact me for other help buthcboucher525@gmail.com I’m pretty flexible with info


That is a great insight. I have always wondered about the impact of the carbon forks and tapered headtubes that we inherited from the industry had on the ride quality of our bikes. If we had the resources, it would be great to start our own test lab. The testing facilities I reached out to were only interested in testing, not doing experiments with us.

So, Firefly just dropped their ti fork and it does exactly what I’m thinking about. Very interesting! Thoughts?


Very cool product. I want one. But $2k minimum is an absurd amount of money for a fork with no moving parts. Still a cool fork.

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and also


I think it’s super cool to have a Ti fork for Ti frames, but in my most judgemental of opinions it doesn’t actually look that great. It seems like the dropouts don’t flow that well into the blade shape. Maybe they’re trying to use different dropout inserts for different rakes but it seems klunky to me.


Well, aesthetics are most definitely subjective! Did you look at the images on their instagram post? The crown looks nice - and they have a pic showing the internal structure. I imagine the fork needs to be chunky due to the nature of titanium. For decades nobody built a ti fork. Drew at Engin says they have a weird springy feel that he doesn’t like (paraphrasing from his interview on Joe’s podcast). If I design something similar in steel I’ll try for a daintier look. But I’m glad to see someone making this approach work; it gives me encouragement to try it.