Hi, I have a summary similar problem, broken right ST-RS685 shifter but with BR-RS785 brakes. I initially bought a ST-R8020 to replace it as couldn't find a new ST-RS685 and only more expensive 2nd hand well used ones. Then found out the ST-R8020 is BH90 rather than BH59 so I bought a new brake (BR-R8070). Then found out the fitting is flat rather than post so bought an adapter. Then found out there is not enough space on the frame to fit the adapter! Bike is a 2015 Cube cross-race. So options I can think of are:

1) buy a 2nd hand BR-RS685 (over £100 for a well used one) - at least I know it'll work
2) upgrade rotor from 160mm to 180mm - think this should work as the post to flat adapter is a lot smaller. Rotor is a centre lock one so am I likely to run into compatibility issues (I'm scarred from this!)? And probably need some more tools?
3) find another B59 compatible dual shifter - all I can find is a ST-RS505 but that's 2nd hand as well, half the price though of the 2nd hand ST-RS685.

All help appreciated.

It does seem that my frame is the problem - guess I could buy new forks? Or buy a new bike if I'm going to run into these compatibility issues going forward!

see if these guys will sell you this... it's quite a bit less expensive... $76, so like, around 57 quid.
that's a great price, btw, so don't hesitate.

https://a.saas-forge.com/products/sh...76-0-0-0-0-0-0

Bit surprised the Cross Race came with Ultegra. My Cross Race Pro of a similar age has 105. Is it definitely that lever?

edit: I see Tredz say the cross race was 195 cable disc and cyclist.co.uk say the Pro that year was Ultegra. Guess yours is a Pro?

So I think the st-rs505 (105) should be fine but the hood shape might be slightly different, that could bother you. I’d be tempted to try the 180mm disc option. But the rotor itself is the best part of £70 I think.

Thanks so much both. I've checked and my bike is a cross race sl - maybe 2016 rather than 2015 (sorry!). I attach the spec I found on the web. I tried to buy the ST-RS685 which sounded the perfect solution but unfortunately they don't deliver to the UK.

So I think I'll go with the 180mm rotor, especially as I have the other new bits anyway. I've researched rotors and found an RT-MT800 for £30 which sounds ultegra level spec (says for MTB but fits road/gravel. Plus another post to flat adapter so only another £40 in total.

Sound the right decision?

Thanks again

As long as there’s enough adjustment leeway to get the caliper 10mm further away from the hub

Hopefully it will - I'll update once I've tried. Fingers crossed!