bigevil

Ok, this one has my head spinning. SRAM tech geeks please any insight!

I have a brand new 2023 S Works Epic Evo LTD ( https://www.specialized.com/us/en/s-...=356880-218876 ) that came with the XX SL Eagle Crankset (this one https://www.sram.com/en/sram/models/fc-xx-sl-d1 ) with a 32T 0mm offset chainring.

I'm looking to upgrade it to a power meter spider to which I need the XX SL Eagle Power Meter Spider (this https://www.sram.com/en/sram/models/pm-axs-spdr-d2 ) and then their thread on chainring to match ( this https://www.sram.com/en/sram/models/cr-ttyp-tm-d1 )

Where things get weird is that supposedly because I'm on 52mm chainline bike (according to specialized) I should theoretically need the 3mm offset chainring but after asking my local spesh dealer and another friend who owns Sierra Bicycle Supply (rad shop btw!) they all say 0mm offset. This contradicts all the support docs and literature about it.

Being new to MTB [and not a SRAM spacing expert] does any of this make sense to anyone here and can someone explain it like I'm 5?

Extremeengineer

According to SRAM LINK your PM crankset has a chainline of 55mm, so seems pretty cut and dried that if you have a 52 chainline now, you need a +3 to pull you back in to 52, since the positive offset goes back towards the centerline of the bike. Scroll down to offset and chainline pics HERE

bigevil

is there a reason why the non power meter XX SL Eagle crankset would have a different width/offset needed? [mine currently has the 0mm chainring on it]

Extremeengineer

If Specialized contracted with SRAM to supply an OEM 52mm chainline version, I haven't heard of that, but it would not be unheard of. Another option is maybe Specialized designed the bike for 52, but the 55 fell within their spec for functionality. So if Specialized says optimal is 52, then you can easily accomplish that with a +3, and so I would think you would just do that instead of trying to set yourself up with an alternate chainline

bigevil

Interesting.... how does one measure to confirm? I'm just confused why they'd be different.

bigevil

SRAM just sent me this, which makes more sense!

bigevil

So the plot thickens (semi).

I think I've spent more time than anyone in the world now reading about the various offsets for their threaded chainring options when installing the transmission power meter spide. this page on PowerMeter City is great but.......

My Epic Evo (which according to specialized is 52cm chainline). The bike came stock with the XX SL Eagle Crankset in 168mm Q Factor with a 32T 0mm offset chainring. (I even verified the Q factor with Sram via the serial number on my cranks) and so based on everything I've seen I should get the 3mm offset right?

Problem is, when I installed it all shifting went to hell, the installed chainguard no longer fit and so I swapped it for the 0mm offset (i'd ordered both) and whala, works perfectly.

Any idea why this is?

I even went to the local Specialized dealer and looked at a bunch of their EVO and Epic Evos with the new power meters already installed and they all have the 0mm offset threaded chainrings.