I have nice ti road bike which is now 5 years old. Both front and rear brakes are shimano r685 post mount. One of the calipers is leaking and the levers are really ratterly,so I’m thinking of replacing them completely. However new users seem to be flat mount calipers. The question I’m asking is can I fit these to a post mount frame with an adaptor?.

You can, eg:

https://www.wiggle.co.uk/shimano-mount-adaptor-front-post-to-flat-road/?lang=en&curr=GBP&dest=1&sku=500057&kpid=500057&utm_source=google&utm_term=&utm_campaign=Shopping+-+All+Products&utm_medium=base&utm_content=mckv%7CsQ3Pt0sef_dc%7Cmcrid%7C295292317327%7Cmkw%7C%7Cmmt%7C%7Cmrd%7C500057uk%7Cmslid%7C%7C&mkwid=sQ3Pt0sef_dc&pcrid=295292317327&prd=500057uk&pgrid=58852352866&ptaid=pla-520919874706&gclid=Cj0KCQjw3Nv3BRC8ARIsAPh8hgKqBspFbagKT0WYAFQ_D3KHygDaeCj7wpnKh3mhs3fOCM0wVTT1lrUaAhVUEALw_wcB

Yes.

That link is for post calipers to flat mount fork I would need the other way round. Flat mount calipers to post mount frame/fork?

The adapter above is the wrong way round – Pm calipers onto FM frame.

It is possible to do the reverse but it’s not pretty and may not fit all frames:

Flat Mount Adapter (140PM-140FM)

If you’re buying new stuff, I’d buy new PM calipers. Looks neater, and probably cheaper.

BR-RS785 look like they are compatible with all current shimano hydro levers.

Or use this as an excuse to get a new frameset with FM & thruA.

That link is what I’m after PDW. Bit pricey though. I’d have thought they must be available in the uk by someone

I’d buy some post mount Hope RX4s. You can always buy an adaptor if you change the frame.

That link is what I’m after PDW. Bit pricey though. I’d have thought they must be available in the uk by someone

I think I may have one of those in the garage spares box, will check for you.

It’s almost certainly easier to put some Mtb calipers on- my cross bike is post mount rear, flat mount front and I’m mix-and-matched on 685 levers.

I’d be curious to try the hopes at some point though, I must admit.

These guys are importing the AS Solutions adapters.

https://spokeydokeybikes.co.uk/

Having recently spent a lot of time and money (unsuccessfully) trying to fit flat mount calipers to an is mount frame i would honestly exhaust all post mount caliper options before even contemplating this.
From what I can acertain flat mount had 3 main design goals, making it cheap for carbon frame manufacturers to fit disc mounts, looking pretty for image conscious roadies and being incompatible with literally everything in order to force people to buy new calipers and/or frames

I’m running shimano 105 hydraulic levers with xt calipers. Buy the shifters you want and sell the flat mount calipers and either buy shimano mtb or hope calipers. I think they are better than road ones anyway

sell the flat mount calipers

Is this even possible? I’m imaging there is a massive oversupply of the things as so many folk in the same boat are trying to get rid of them.

If Shimano have built in their patented slow leak feature then yes should be easy to sell them on.

Exactly the same problem here! Eventually found two hope rx4s but the rear wouldn’t fit onto my frame so ended up with rx4 front and r785 rear. Both are fine. Although I have a supply of o-rings on hand for when the 785 leaks…
Shimano have a compatability chart that tells you what calipers and levers work together – easy to find if you Google it.

most makes are doing post/flat mount interchangeably – sram rival for eg

Bracket (Disc Brake) Direct mount DIR, Flat Mount 20mm offset, Flat Mount no offset, Intl Std(140mm Rear,160mm Frt rotor) 0IS, Intl Std(160mm Rear,180mm Frt rotor) 20I, Post mount (20mm bracket) 20P

time for Di2?

https://www.probikekit.co.uk/bicycle-brakes-and-pads/shimano-st-r785-hydraulic-disc-brake-di2-sti-s-pair/11211776.html

Otherwise i’d just get set of Ultegra hydro STis and a pair of Deore calipers

https://www.fawkes-cycles.co.uk/2498624/products/shimano-deore-m6000-caliper-front-or-rear-black-one-size-post-mount.aspx

Or as others have said, upgrade to hope rx4’s

https://www.merlincycles.com/hope-rx4-caliper-complete-125534.html?utm_source=PHG&utm_medium=AffiliateMarketing&utm_campaign=phg-GB&ucpo=59294&source=PHG

You can get BR-RS785 calipers if you want something that’s “road branded”. I bought an XT caliper.

I suspect that the 2nd hand market for FM calipers is pretty strong, as I’ve certainly had pair of FM calipers develop the dreaded Shimano seal leak, and there will be people looking to upgrade to a FM frame and move existing kit across.

When I did this, it was cheaper to buy the levers with calipers anyway and the price of the adapters quickly eats into any savings.