Brake 203mm adapter sizing for Fox36+SRAM?

[phillynight]

I'm running a 2021 Fox 36 with SRAM G2RS brakes and a 203mm rotor. I did research and thought I got the right adapter (Shimano SM-MA-F203P/PM) but after starting the bed-in I notice the pads aren't using the full rotor patch. Am I using the wrong adapter or is this path of rotor usage 'normal'?

 

[Tubbsy]

I think you need this one:

Shimano Post Frame Or Fork To Post Caliper Brake Mount

Post to post brake mount to mount your caliper for a rotor size, dependent on what rotor you have, and what your fork/frame has as standard.Ultimate adaptors are XTR level and use a lighter alloy with more cutouts to save a couple of grams in weight. F 160-180mm - R 140-160mm 160-180mm: +20mm...

www.mtbdirect.com.au

 

[leitch]

Hah, yeah I did this too when I went from Fox 34 - 36 without thinking/checking. The 36 is a 180mm post mount (i.e. minimum rotor size is 180mm) so you need a smaller adapter to go up to the 203mm.

 

[phillynight]

Hmm so which one do I need? The one I got looked like it was supposed to go from 180-203 ?

 

[leitch]

Yeah actually just checked @phillynight and I'm running the same adapter on my 36 with 203mm rotor no problems (XT 4pot brake though not SRAM). Seems odd... what's the rotor? It's definitely not SRAM.. might be a rotor:caliper compatibility issue?

 

[phillynight]

Okay that's weird, so I then have to wonder if Shimano and SRAM have a different idea of what 23mm is ?

It's just a plain old (new) Disco rotor (https://www.discobrakes.com/)

 

[Tubbsy]

The one I linked is what I'm using on my Mezzer with 203 rotor.

 

[Isaakk]

The stack height for 203mm looks alright (at least for shimano) - I run the same adapter on Pikes to go from 180->203mm with an SLX caliper + 203mm IceTech rotor and it works just fine.

Maybe measure the rotor diameter to see if it's actually 203mm?

 

[Tubbsy]

Or hang on, is that link just giving you all of them? I might have to check what's written on it exactly.

 

[Isaakk]

If going from 180 -> 203 the cleanskin is the cheapest choice (link - you'd want mount B), but in theory it should be the exact same as the Shimano one you already have.

I have a suspicion that the rotor is actually 200mm.

 

[phillynight]

Well I just pulled the rotor off hoping it was 200 (which would make the most sense) but measured and it looks exactly 203mm. There is about 3-4mm of rotor that the pads aren't touching... maybe I just start shaving down the Shimano adapter until I get it right?

 

[Isaakk]

Another thought I had - which pads are in the calipers?

 

[Minlak]

Am I missing something here? I have always used Sram adapters with Sram brakes and Shimano with Shimano - I was under the impression they were slightly different? Are they meant to be the same?

 

[Staunch]

The Shimano SM-MA-F203P/PM is a +23mm mount. While technically you've made the correct choice, the SRAM/Shimano combo maaay have something to do with it, I'm not really sure tbh.
I'd try a +20mm mount like a SM-MA-F180P/P2 or the SRAM equivalent to bring that caliper in closer.

 

[ozzybmx]

... maybe I just start shaving down the Shimano adapter until I get it right?

That's what I would be doing, then touch up the raw edge with a black pen.

 

[phillynight]

The Shimano SM-MA-F203P/PM is a +23mm mount. While technically you've made the correct choice, the SRAM/Shimano combo maaay have something to do with it, I'm not really sure tbh.
I'd try a +20mm mount like a SM-MA-F180P/P2 or the SRAM equivalent to bring that caliper in closer.

Okay, I think you guys are right... I assumed 23mm was fucking 23mm hahah the variation in MTB specs ABSOLUTELY fucking pisses me off. So it seems that according to SRAM if you have a 180 Fork and want to run a 203mm rotor, then you have to use a 20mm adapter like this one. I'm not sure who the mathematician over at SRAM is

 

[Oddjob]

Okay, I think you guys are right... I assumed 23mm was fucking 23mm hahah the variation in MTB specs ABSOLUTELY fucking pisses me off. So it seems that according to SRAM if you have a 180 Fork and want to run a 203mm rotor, then you have to use a 20mm adapter like this one. I'm not sure who the mathematician over at SRAM is

The guys in SRAM who can math are in marketing and finance.

It's all about the vibe in engineering.

Sent from my SM-G970F using Tapatalk

 

[Minlak]

Am I missing something here? I have always used Sram adapters with Sram brakes and Shimano with Shimano - I was under the impression they were slightly different? Are they meant to be the same?

Just quoting this to point out I said this way back up there and no one paid me any attention - what kind of forum is this?

 

[The Duckmeister]

The guys in SRAM who can math are in marketing and finance.

It's all about the vibe in engineering.

Sent from my SM-G970F using Tapatalk

They're American, therefore still haven't managed to get their heads around the Metric system.....

 

[Staunch]

Just quoting this to point out I said this way back up there and no one paid me any attention - what kind of forum is this?

At the end of the day a +20 is a +20 no matter what the brand. I've used SRAM post mount adapters with Shimano calipers to go from 160mm to 180mm no problem. I think the only issue is when you transition from 180mm to 203mm, and yet still only need a 20mm difference with SRAM calipers.