If you are reading this than you have likely noticed that there are not a lot of options for someone who wants to use flat mount caliper on a post mount frame/fork. This is probably because it is very difficult for a manufacture to guaranty compatibility. However it may be possible, but it will depend on your frame/fork and the size of the rotor that you want to use. This guide is meant to help you determine which adapter you need and if it will work with your frame/fork.


Post Mount Size

The first step is to determine which size post mounts you are using. The post mounts on most road or cyclocross frames have been designed for either 140 mm or 160 mm rotors. You can use the dimensions shown below to help determine the size of your post mounts. Dimensions “A” and “B” are measured in a straight line from the center of the axle to the center of the mount hole. It is difficult to measure these dimensions exactly but you should be get close enough to determine the post mount size.

Frame/Fork Compatibility

PM-FM Adapter:

  • 140 mm. Post Mount – works with 140 mm. rotors
  • 160 mm. Post Mount – works with 160 mm. rotors
  • 180 mm. Post Mount – works with 180 mm rotors
  • You need at least 24 mm. clearance between posts.

PM-FM+20 Adapter:

  • 140 mm. Post Mount – works with 160 mm. rotors
  • 160 mm. Post Mount – works with 180 mm. rotors
  • 180 mm. Post Mount – works with 200 mm. rotors
  • You need at least 13 mm clearance between posts.

Caliper Compatibility

The adapters were designed to have enough clearance for Shimano calipers. Most other calipers are smaller and should work without problems.

Campagnolo: Rear 140 mm calipers should work with all our adapters. Rear 160 mm calipers will only work on a 140 mm post mount frame with a 160 mm rotor, if you use the PM-FM adapter. Front calipers won’t work with our adapters. (Ekar calipers will work with all our adapters.)


You can also download a drawing with the images from this page.


The drawing is 1:1 scale so If you print it on the correct size paper should be actual size. You can cut out the adapter you want to use and hold it up to the frame/fork to get a better idea if it will work.

Flat Mount Adapter Drawing - Cutout

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