How do I choose the correct disc brake adapter?

With this article, we want to give you all the knowledge and understanding you’ll need to be able to identify which brake mount standard you have, and which adapter you need based on the disc brake rotor size that you intend to use. It’s important to understand the 2 most common disc brake mount standards we currently offer in our adapters - International Standard (IS), and Post Mount (PM).

Post Mounts

Post Mounts feature 2 threaded posts that stand off either the frame or fork. Up until around 2018, pretty much all suspension forks and frames would use a 160mm or PM6 direct mount. Now, with many bikes such as Enduro bikes becoming specced with larger disc brake rotors, you often see 180mm or PM7 direct mounts fitted to frame and forks too, so can be a little more confusing as to which direct mount size you have. Beyond this, 203mm or PM8 direct post mounts can be found on bigger travel suspension forks such as the Fox 40, where the caliper would bolt directly to the fork without the use of an adapter when running a 203mm disc brake rotor.

This image illustrates a 160mm or PM6 direct mount fork using a 160mm disc brake rotor. In this setup, no brake adapter is required, as the brake caliper direct mounts to the fork.

a disc brake caliper directly mounted to a bicycle frame with a 160mm rotor
a 160mm disc brake adapter mounted onto a frame with finned pads in a caliper

This image shows the installation of our 180mm disc brake rotor with a PM6 fork. With this setup, the adapter you need would be a Post Mount 6 to 180mm or PM6/180, so the first part stating PM6 refers to your frame or fork direct mount size, and the 180 part is the disc brake rotor size you intend to fit.


This image shows the installation of our 203mm disc brake rotor with a PM6 fork. With this setup, the adapter you need would be a Post Mount 6 to 203mm or PM6/203, so the first part stating PM6 refers to your frame or fork direct mount size, and the 203 part is the disc brake rotor size you intend to fit.
a 220mm disc brake adapter mounted onto a frame with finned pads in a caliper

This image shows the installation of our 220mm disc brake rotor with a PM6 fork. With this setup, the adapter you need would be a Post Mount 6 to 220mm or PM6/220, so the first part stating PM6 refers to your frame or fork direct mount size, and the 220 part is the disc brake rotor size you intend to fit.

International Standard

a rear 180mm international standard disc brake adapter mounted onto a frame with finned pads in a caliper

 

International Standard mounts are the unthreaded tabs found on either a frame or fork. These allow for the brake adapter to be bolted to the IS tabs, then the brake caliper is bolted to the adapter. These adapters are front and rear specific, so an adapter for a fork would require a front, and the frame a rear adapter. Current fork manufacturers use almost exclusively post mounts now, but IS mounts are still commonly used on the rear of frames. As an example, if you were looking to install a 180mm disc brake rotor onto an International Standard fork, you would need a Post Mount to International Standard Front 180mm, or PM/IS-F180.


Note - Always check the frame and fork manufacturer specifications on the maximum rotor size you are permitted to fit, as exceeding the maximum specified size may result in frame/for damage.
Adapter Type PM to PM +20mm PM to PM +23mm PM to PM +43mm PM to PM +60mm PM to PM +40mm
Also known as PM6/160 to 180mm PM7/180 to 203mm PM6/160 to 203mm PM6/160 to 220mm PM7/180 to 220mm
Used For Increases rotor size by 20mm on a
Post Mount fork/frame with post mount
brake caliper 		Increases rotor size by 23mm on a
Post Mount fork/frame with post mount
brake caliper 		Increases rotor size by 43mm on a
Post Mount fork/frame with post mount
brake caliper 		Increases rotor size by 60mm on a
Post Mount fork/framewith post mount
brake caliper 		Increases rotor size by 40mm on a
Post Mount fork/frame with post mount
brake caliper
Common Rotor Sizes
based on *native mount
size 		160 → 180
180 → 200
200 → 220 		180 → 203
200 → 223 		160 → 203 160 → 220 160 → 200
180 → 220
Required Bolts 1x M6x38mm / 1x M6x32mm 1x M6x38mm / 1x M6x32mm 4x M6x20mm 4x M6x20mm 4x M6x20mm
Front or Rear Fitment Both Both Both Both Both

*Note: A native brake mount size indicates the minimum disc rotor size compatible with a frame or fork. When the brake caliper is attached directly to the mounts, without the use of adapters or spacers, the rotor is positioned perfectly within the brake pads.

 
Adapter Type PM to IS Front 180mm PM to IS Front 203mm PM to IS Rear 160mm PM to IS Rear 180mm PM to IS Rear 203mm
Used For Allows fitment of a 180mm rotor
on an international standard
fork mount with post mount
brake caliper		 Allows fitment of a 203mm rotor
on an international standard
fork mount with post mount
brake caliper		 Allows fitment of a 160mm rotor
on an international standard
rear frame mount with post mount
brake caliper		 Allows fitment of a 180mm rotor
on an international standard
rear frame mount with post mount
brake caliper		 Allows fitment of a 203mm rotor
on an international standard
rear frame mount with post mount
brake caliper
Required Bolts 4x M6x20mm 4x M6x20mm
 4x M6x20mm
 4x M6x20mm
 4x M6x20mm
Front or Rear Fitment Front Only Front Only Rear Only Rear Only Rear Only
Adapter Type FM to FM 140 / +20mm 160mm FM to FM 180mm Front +40mm FM to FM 160mm Rear +20mm FM to FM 180mm Rear
Used For Depending on which way you install
this mount, it allows you to either mount
a flatmount caliper without increasing
rotor size from the native mount size,
or increases the rotor size
by 20mm on a Flatmount fork with
Flatmount brake caliper 		Increases rotor size by 40mm on a
Flatmount fork with Flatmount
brake caliper		 Increases rotor size by 20mm on a
Flatmount frame with Flatmount
brake caliper		 Increases rotor size by 40mm on a
Flatmount frame with Flatmount
brake caliper
Common Rotor Sizes
based on native mount
size		 140 → 140
160 → 160
140 → 160
160 → 180		 140 → 180
 140 → 160
160 → 180
 140 → 180
Front or Rear Fitment Front Only Front Only Rear Only Rear Only
Adapter Type FM to PM 140 Front FM to PM 160 Front +20mm FM to PM 180 Front +40mm FM to PM 140 Rear FM to PM 160 Rear +20mm FM to PM 180 Rear +40mm
Used For Allows fitment of a Flatmount fork
with post mount brake caliper
without increasing rotor size from
the native mount size		 Increases rotor size by 20mm on a
Flatmount fork with post mount
brake caliper		 Increases rotor size by 40mm on a
Flatmount frame with Flatmount
brake caliper		 Allows fitment of a Flatmount frame
with post mount brake caliper
without increasing rotor size from
the native mount size		 Increases rotor size by 20mm on a
Flatmount frame with post mount
brake caliper		 Increases rotor size by 40mm on a
Flatmount frame with post mount
brake caliper
Common Rotor Sizes
based on native mount
size		 140 → 140
160 → 160		 140 → 160
160 → 180
 140 → 180
 140 → 140
160 → 160
 140 → 160
160 → 180

140 → 180
Front or Rear Fitment Front Only Front Only Front Only Rear Only Rear Only Rear Only

*Note: A native brake mount size is the minimum disc rotor size compatible with a frame or fork. When the brake caliper is attached directly to the mounts, without the use of adapters or spacers, the rotor is positioned perfectly within the brake pads.