I'm building up a road frame with IS disc mounts and would like to use the Ultegra R8020 groupset (with newest gen hydraulic discs). These disc calipers are flat mount, but in the product specifications, the Shimano website has the cryptic added comment "(available for IS mount with mount adapter)". I don't see any available flat-to-IS mount adapter from Shimano or anyone else. Does that comment mean there are substitute calipers that are IS-compatible or is there a flat-to IS adapter that I haven't found?

I've looked, and so far as I've found, there are no adapters to "retro" a flat-mount caliper to an IS or post-mount frame. There are adapters to put traditional post-mount calipers onto flat mount frames, but not the other way around. If you have the frame you want, the easiest (and cheapest) option is to use different calipers.

TRP has a direct to post mount adapter I assume direct mount bolts all follow a standard internationally for cross market compatibility
as does ISO and post mount..

Maybe the MTB hydraulic caliper would be compatible with the road master.. Shimano, + Magura , TRP use mineral oil..


TRP, Hylex is their road disc hydraulic ..
https://www.trpcycling.com/wp-conten...-FM-160602.pdf

HyRd is their cable operated hydraulic
https://www.trpcycling.com/wp-conten...-FM-160602.pdf

Note; there is an adapter even for direct mount 1 for each disc size ..





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Just went through this. I ended up buying the groupset in pieces instead of a single package, which worked out OK since I set the bike up for 1x. You can use the new Ultegra brifters, but you will either need RS685 or XT calipers.

Per TRP, "Adapters to convert flat mount forks or frames to post mount for 140mm and 160mm rotors."

The adapters are to put post-mount calipers on flat mount frames. There is currently no way to put a flat mount caliper on a post or IS mount trame.

That would be a mistake, the same thing is also on the MTB brakes that are PM, you can attach PM brakes to IS mounts with adapters, there is no adapters for attaching FM brakes to IS mounts.

https://productinfo.shimano.com/#/spe...20disc%20brake)

Give up on the idea of attaching FM calipers and get some PM calipers instead.

Here's some flat mount to post mount adapters.

https://www.assolutions.ca/product-category/adapters/


It might be possible to attach the FM to PM adapter onto a PM to IS adapter but it would probably mean a increase of rotor size.
I doubt those FM to PM adapters would fit on a F160/R140 PM to IS adapter, they mightn't even fit on a F180/R160 PM to IS adapter.

At least someone is making adapters-- but on an IS frame, it would still not be possible, as the flat-mount adapters require vertical clearance, and IS adapters are usually nearly flat (except for those for 203 rotors.) It's still just easier to buy post-mount calipers and sell the 8070s. 685s, 785s, or XTs are all around 50 bucks each, sometimes less-- and won't require double adapters.