[Closed] Road flat mount/post mount confusion

You need something like this, assuming there are no issues using a Shimano adaptor with Sram callipers -

https://www.sjscycles.co.uk/brakes/shimano-adapter-for-post-type-caliper-140mm-flat-type-frame-mount/

Thanks, I can see that will sort the rear.
Might have to find it cheaper than £24 though!?

Merlin have them for £7

Thanks, they have a TRP rear one in stock but this Shimano one says post to flat mount but the image looks like a post to post mount? Each set of holes is the same distance apart? Maybe the pic or description is wrong?
https://www.merlincycles.com/shimano-disc-adaptor-post-to-flat-mount-99268.html

That link is a front fork mount adaptor. You don't need a front adaptor to run a post calliper on post fork with 140mm rotor.

Well the body of the caliper around the piston extends below the line of the post mount holes, there has to be an adapter between fork and calliper.

Are you sure the fork is post rather than flat mount?

The fork attachment for flat mounts uses bolt spacing which looks similarly spaced to post. Also, you would usually bolt a post mount straight on, so if there's insufficient room to fit the calliper it sounds like something strange is going on.

Well the body of the caliper around the piston extends below the line of the post mount holes, there has to be an adapter between fork and calliper.

Need pictures. It should just bolt straight on.

See page 6

Right I think I’m getting there (or going mad)
No a flat mount brake will bolt straight on but mine is post mount looks like this:

But my fork looks similar to this one

So that is flat mount? Where I got confused is front flat mount holes are the same distance apart as post mount calipers!? The rear flat mount holes are closer together.

My caliper will not bolt straight on,it needs an adapter to clear the piston body and bring the caliper far enough away for pads to line up. Flat mount calipers are already tilted to bring the pads further out to line up with the disk.

I'm amazed that framesets are still being supplied with this strange mix of brake mounts.
It's not really a satisfactory solution to fitting a pair of flat mount calipers, and is just laziness on the part of the supplier

Frame comes with front and rear 140/160 adapters clearly marked for whatever disk combination you want as long as it’s flat mount.

I’m using second hand brakes, would be good to go if I had new flat mount callipers.

Reminds me of the IS mount changeover with MTB years ago

That's a flat mount fork so you DO need an adaptor. That Merlin link is correct.

So that is flat mount?

Yes

You need a TRP FF1 if you can find one...

https://www.upgradebikes.co.uk/Catalogue/Disc-Mount/Flat-Mounts

Thanks, I assumed flat was the same front and rear which added to the confusion.

@MrSmith, your original post seems to contradict your recent post...

Forks have a post mount (holes Sam distance apart as calliper)
Frame is Flat mount (holes close together)

Frame comes with front and rear 140/160 adapters clearly marked for whatever disk combination you want as long as it’s flat mount.

Now that it appears you have flat mount all round, my statement doesn't apply

I didn’t explain it very well, should have said ‘as long as your brakes are flat mount’

I guess once you are up on all the mounts and sizes it’s less confusing, even the sram pdf above shows different spacers and adapters but just tells you distances in mm for each bolt, no mention of what disk/caliper/mounts combo works.

Now know what I need so thanks for input.
Now I just need to work out what length bolts I need...

Thanks, I assumed flat was the same front and rear which added to the confusion.

No, it's quite confusing! The bolts for FM calipers screw into the bottom of the caliper.

On the front, the caliper bolts onto an adapter plate which then bolts on to fork in a similar way to a PM caliper i.e bolts from the rear. The adapter plate can be reversed to swap between 140mm and 160mm.

For the rear, the caliper bolts directly onto the frame, with the bolts going through the chainstay from the underside.

For added fun, there's no standard depth of chainstay, which means that you need to get the right bolt length to match your frame.

It looks like that Shimano adapter above swaps one of the PM bolts for a stud and nut, presumably because otherwise the bolt would hit the frame.

Ah - the flat mount bolt length dilemma.

The designated length refers to the thickness of the chain stay where the bolt goes through - it has nothing to do with the actual length of the bolt.
Don't ask me how I know this, and don't ask my LBS how many visits it took to work this out

bit of measuring and internet searching and i have ordered some bolts.
found this shimano PDF handy as it shows you the chain stay width and bolt length options.