flat mount frame, post mount brakes (road) – adaptors questions

I can see that adaptors exist but much more available for front brakes.

How are we with current “standards”  – is there an actual difference between front & rear flat mount standards ?

(in the good old days of IS you could shove the same adaptor in either end and it would work but for different rotor sizes)

The flat mount brakes are the same, but the front needs an adapter as most forks you can’t bolt through from the front so you bolt the adapter plate to the fork with the caliper attached, this is reversible 140mm one way up the other 160mm.  The rear is 140mm standard bolted straight to the frame and a spacer to go 160mm.

These are Shimano standards.  Hope’s RX4 flat mount is native 160mm front and rear.

Cheers B-S, but either I don’t understand what you’re saying or I explained myself badly at first.

If I want to use F&R 160mm rotors with my old post-mount brakes but on a frame that has flat mounts, can I use, say, two of these:

https://www.westbrookcycles.co.uk/cannondale-160mm-flat-mount-to-post-mount-disc-brake-adapter-p333329

Front and rear flat mounts are different.  The callipers are often the same but require adaptors to make them work with either end and different size rotors.  The difference (as above) is that Hope have specific callipers front and rear for flat mount.

Shimano do flat mount > post mount adaptors for front and rear, both are on CRC and wiggle for about £15-£20 each.

alternatively, you could just buy a set of new RS805 callipers (flat mount) from eBay, for about the same price.  Assuming you have Shimano that is.

WTF is this ?

Aha – these ? :

https://www.tritoncycles.co.uk/components-c9/disc-brakes-c58/flat-mount-adapter-for-post-mount-caliper-p18911

This explains it :-

Road Disc Brake Tech: Flat-mount vs Post-mount

Beware that allthough rear adaptors exist, they may not physically fit in the frame, especially smaller sizes. Most frames with a seat tube smaller than 54cm have curved seat stays to fit around a FM brake, and there’s no way an adaptor + PM caliper will fit, it will hit the seat stay.

WTF is this?

A captive bolt that your post mount brake slides onto and then a nut is placed atop it.  There’s not enough space to allow for a threaded bolt to screw down through the brake into the adaptor (as per normal) without hitting the frame.  This is the solution.

Thanks everyone – stuff to read and everything !