So it would appear from the Tiagra thread that they are flat mount only, same as the new Sora kit released earlier this year.

If this continues, where does this leave existing post mount road disc users when their calipers need replacing?

Isn’t it just an adaptor, and worse case, a bigger rotor?

Deore/Alivio calipers?

Presumably you can use MTB calipers (or are the pistons different sizes? [edit] I know they are for SRAM [/edit] ), hose/fittings compatibility is an issue also with the road hyd-shifters.

But regardless shimano will likely still offer post mount calipers for systems where they have already supplied them, just not at tiagra level, which has come in not flat-mount is a thing. Obviously not much help for people with older frames using post mount, but shimano arnt known for making new stuff backwards compatible.

Isn’t it just an adaptor, and worse case, a bigger rotor?

You can fit post mount caliper to a flat mount frame, but the calipers are not backwards compatible, or at least there isn’t an adaptor available right now.

Yep, just found that out. Looks like the options are SRAM or mtb calipers then.

Love the idea of disc brakes road bikes but glad I decided to hold off until standards settled down.