I bought a cheap 28" steel fork to replace a rusted 26" suspension one on an old Trek MTB for my kid. The geometry looks good, but I can't align the the disc brake caliper properly. The pads end up outside the rotor.

I have a couple of different IS-adapters but none work. To me it seems that this 160 mm rotor can't work with the fork's IS-mount. Should I consider a bigger rotor? Is there a problem with the fork, or could the cheap zoom caliber be the problem? Am I missing something?

Pictured below is what I think would be the optimal position for the caliber. I haven't found an adapter online that would position the caliper as pictured.

optimal caliper position

  • Are you able to provide Make/model and/or specs for the fork?
    – mattnz
    Commented Mar 28, 2023 at 3:01
  • It's an M-Wave Trekking Fork 28" bike-discount @mattnz
    – Panmanp
    Commented Mar 28, 2023 at 11:38

3 Answers 3


It looks to me as if the fork was built to take a larger rotor. You might find the cheapest/simplest solution is to change the 160mm rotor for a larger one. You'll need to measure up to see how much larger.

  • Good overview here. bicycles.stackexchange.com/questions/44161/…. @Nathan Knutson says that 160 is the minimum front, so I take that to mean 180 could be the minimum for that fork.
    – mattnz
    Commented Mar 28, 2023 at 3:00
  • @MaplePanda I think 160mm is the minimum size for a front rotor with an IS mount caliper. In this case, a larger rotor would mean that the caliper could be mounted on the existing adapter - so instead of moving the caliper in (towards the hub) with an adapter the OP can't find, I'm suggesting moving the rotor's braking surface out by using a larger diameter rotor. Commented Mar 28, 2023 at 9:59
  • @GregShailes Oh my goodness, I somehow misinterpreted the question as left-right misalignment. Total cock-up.
    – MaplePanda
    Commented Mar 28, 2023 at 18:34

Getting a bigger rotor (180 mm) and using some cup and cone washers from old v-brakes did the trick.

I know it's not perfect, but it seems to work with my 100 kg so should be fine with my 35 kg kid.

enter image description here


Front and rear is not the same. If you get the correct adapter it is likely to work.

You seem to be testing a few different IS adapters. It would to me make sense to use a front IS to PM 160mm adapter.

  • 1
    Hi, welcome to bicycles. In this case the difference is between two different forks, so the rear doesn't enter into it.
    – DavidW
    Commented Mar 27, 2023 at 10:59

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