203mm rotor post mount adaptor

[Tubby G]

Hi Forum

I’m having an issue fitting a 203mm Magura rotor to my partner’s Rise with FOX 34 forks

The adapter I bought is the incorrect size. I purchased the Magura 180-203mm QM44 adapter

My Rise has the FOX 36 forks with 203mm rotors, and uses the Shimano SM-MA-F180P/P2 adapter (fitted in Orbea factory)

when holding the two adapters side by side, they’re exactly the same size, and the new Magura adapter fits my FOX 36 forks absolutely fine

However, I have now noticed the post mounts on the FOX 34 forks are in a slightly different position to the FOX 36 mounts

So question is, has anyone converted their 180mm rotors to 203mm rotors on their FOX 34 fork and if so what adapter did you use ? Thanks

 

[Tubby G]

I think I need a 160-203mm post mount adapter, as the pre 2022 FOX 34 fork is meant for 160mm rotors without adapters

 

[Tubby G]

Right then, what I have discovered using google …

FOX 36 has a PM7 mount for 180mm rotors, callipers will fit directly to fork mounts, anything larger requires an adapter

FOX 34 has a PM6 mount for 160mm rotors, callipers will fit directly to fork mounts, anything larger requires an adapter

The adapter I believe I require is the Magura QM42, which is for 160-203mm

Shimano also make the adapters, as do many other third party companies such as Uberbike / DiscoBrakes etc

This document is useful:

https://www.magura.com/media/1061051/2019-08_mounting-guide.pdf

 

[JCU Delt Ox]

@Tubby G It looks like you're now well educated. It all comes down to the native rotor size for the fork. The 34 takes a 160 with no adapter, the 36 minimum is 180. You run into the same issue on the rear depending on what frame you run. Now you know.

 

[Tubby G]

Just to finish off this little story. Magura QM42 post mount bracket arrived today. This is the correct mount for FOX34 forks if upgrading to 203mm rotor

The bracket only came with two screws though, to mount the bracket to the fork mounts. You still require the same size screws to mount the calliper on to the bracket. I just used the screws that came with the 180mm mount but had to cut them down to length with a hacksaw