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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?

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  • 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
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    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

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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.

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