Shimano 105 Hydro question – post-mount / flat mount.

Hello. Having trouble finding answers from Google and for some reasons brake standards confuse me. Wondering if anyone here can help:

I am thinking of making the switch on my gravel / cx / road bike from the slightly knackered mish mash of Sram Rival 1x (With the 3-storey reservoirs) to a more roadieesque 105 Hydraulic groupset. Normally would be totally fine at swapping this over – however:

It is a relatively old frame (Trek Crockett 7 Disc) which has post-mount, whereas all the modern bikes have flat-mounts.

Am I right in thinking there is no adapter to account for this?

And if that is the case – am I right in thinking that there is a only 1 certain post-mount shimano caliper which can be hooked up to the road hydro levers? Or can I just get some, say, Deore calipers and hoses and plumb them into the new levers?

I think all shimano calipers are interchangeable as long as you match the hose/fittings. I’ve had a ‘roadie’ caliper (rebranded xt as ultegra as far as i could tell) and a Deore with 685 levers with no problem.

Alternative 1: there are post mount frame to flat mount brake adapters. Either expensive from wolftooth or cheap from amazon/ebay. I bought a cheap one for an old frame and while haven’t actually used it yet can’t see any reason why it wouldn’t work if the limitations on rotor size work for you (IIRC mine was a 140mm post mount and this bumped it to a 160mm flat).

Alternative 2: buy hope RX4s.

Just on the Hope RX4 suggestion I’d avoid them like the plague. Had no end of issues with them leaking / losing power etc. They were very powerful when working but just not worth the bother. Gone back to Ultegra calipers which feel slightly underwhelming power wise vs the Hopes but they’re the same everytime I use them with no faffing about.

If I were to want to try a more powerful caliper now I’d be giving the Magura flat mount calipers a go personally.

You could use the Ultegra/non-series one…

https://bike.shimano.com/en-EU/product/component/ultegra-6870-di2/BR-RS785.html

https://www.sjscycles.co.uk/brakes/shimano-brrs785-road-post-mount-hydraulic-disc-brake-caliper-front-or-rear/

That sucks. Must say mine have been pretty much forgettable in the year since i installed them. Although that process was annoying and a faff!

I’ve got Tiagra 4720 levers paired with TRP hylex calipers currently, which work, maybe a bit of a mismatch in terms of piston size and therefore volume making the, a little mushy on initial bite, I am tempted to go and find some cheap MTB calipers (Deore or lower tier) or some Ali-Express specials to try as I think those have the same diameter pistons as the stock road equivalents (don’t quote me on that)

There are/were definately 105 and Ultegra PM Calipers available when they first released the hydraulic braked groups, you should be able to track those down (a mate has the 105 on his older Arkose and I rented a Synapse with PM ultegra on holiday once, so they definitely exist).

Any FM to PM adapter is probably going to increase the rotor size (to like 180mm?) which you might not want, then again you might(?).

Thanks for the input all. I think I will probably just buy some rather cheap off-model Deore-level calipers or something and plumb them in. Not sure I want to go down the massive rotor route on this bike, 160s will be fine for me.

https://www.merlincycles.com/wolf-tooth-post-to-flat-mount-brake-adaptor-271466.html

Wolf Tooth adapter is what you need! Or as others have said, switch the calipers.

Deore / Shimano MTB Calipers work absolutely fine.

I’m also interested in this as I’m planning on doing similar. In my case I’ve an old steel all road bike with IS mounts. I’ve picked up some used RS-405 (non series Tiagra 4700) gears/brakes that I’m looking to fit to replace the Sora/Juin Tech post mount setup.

I’ve seen that you can get IS to flat mount adapters from AliExpress, but the Deore MT410 post mount calipers are available in the UK for under £20 an end. MT200 calipers are even less, but I think the MT410 is a stronger brake? One of my flat mount calipers is seized, so I’m going to replace the both calipers. Hopefully it’ll all work.

@dewd – Wouldn’t recommend getting MT200 anything. They came on an old MTB of mine and they were dreadful.

Granted, that was mostly the long lever being big and flexy that you’d change, and you don’t really need “stop dead in the middle of a rocky chute” power on a road bike as with an MTB so YMMV with those. In fact with good pads they’d probably be fine, just heavy and not as durable.

@dewd – Wouldn’t recommend getting MT200 anything. They came on an old MTB of mine and they were dreadful.

Granted, that was mostly the long lever being big and flexy that you’d change, and you don’t really need “stop dead in the middle of a rocky chute” power on a road bike as with an MTB so YMMV with those. In fact with good pads they’d probably be fine, just heavy and not as durable.

Cheers. I’ll order the MT410s.

I use R7020 levers with RS785 calipers on my road bike. They work well.

You can also get flat mount caliper to post mount frame adapters on UK eBay as well as AliExpress. Note that apparently they don’t work for all calipers.

@elray89 was thinking about this the other day….  Did you buy a full groupset and have the calipers ‘spare’ as it were? As I’m in need of some flat mount calipers.

I have previously done the opposite and thus im pretty sure i have a pair of new Deore M6000 post mount calipers in my spares box… a swapsie might work for both of us….?

@snotrag – I’ve not bought anything yet…but interesting proposition and will keep you in mind!

Slightly left of centre but …

What about cable 105 brifters and some TRP cable callipers in post mount variant.

I find the breaking ( power, modulation ) very similar to my Ultegra hydro brifters.