I have a cyclocross bike built on Shimano 105 (~2018), but the frame was too big for me, so I decided to buy a smaller one on the aftermarket and just move all my existing stuff to this frame. I found matching offer, checked the frame specs on the frame manufacturer's website and bought it. Upon arrival, it turned out that specs were totally wrong. For example: manual said that the fork uses 12mm through axle, but in reality it was 15mm. And currently the biggest problem for me: the frame uses 140mm post mount, while my current brake system is 160mm flat mount hydraulic brakes(BR-R7070).

Apart from selling this frame and looking for another one, what are my options? I have already found the conversion set for fork, but brakes keep me wondering: can I simply buy a new post mount caliper? Will it even work?

I also know that different brake systems from Shimano use different hydraulic hoses. How important this is? Can, for example, BR-RS785 caliper work with ST-R7020 levers?

  • Which country is it? In many countries you can return mail order purchases no questions asked, and wrong advertised information could well be a reason to return.
    – ojs
    Commented Jul 11, 2021 at 9:23
  • It is Germany. But the seller is a private person. So they won't accept returns.
    – AM5800
    Commented Jul 11, 2021 at 15:20
  • 1
    In Germany, even private sellers have to accept a return if the item was incorrectly advertised! There's just no warranty and no 14-day return-period if you happen to dislike the article. Selling something that doesn't match the description is basically a scam, and that's illegal for private sellers just as well.
    – Erlkoenig
    Commented Jul 11, 2021 at 19:03

1 Answer 1


You can try these PM to FM adapters. If the adapters don't work, you can always sell BR-R7070 and get any Shimano PM calipers, these are all cross-compatible, including BR-RS785.

I also know that different brake systems from Shimano use different hydraulic hoses. How important this is?

Not really important. BH-59 and BH-90 have different internal diameters, so you'll need to use different barbs. I noticed no difference when going from one to another.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.