104/64bcd Crank Question

[Coal Bee Rye Anne]

I'm curious whether anyone could confirm or deny if all 104/64bcd cranks are created equal with middle/outer chainring compatibility or whether there are possibly some variances in spider/shelf design?

The reason I ask... and this is purely academic at this time as I've no real need/time/expense to fully pursue any projects right now... is that I just now became aware of a spec/design feature of my Deore LX FC-M571 Octalink triple crank which actually has a different shelf height on the middle and outer part of the 104bcd spider.

I came to this realization after recently cleaning and mocking up my spare crank for a potential 2021 build.  I originally acquired this crank used as a 22-32-44 triple on a hand me down frame plus parts and turned it into a 32t bashguard sandwiched 1x crank for a while and then had picked up a 64bcd 32t inner ring (see example in the link below) and temporarily set it up as a 32t-32t-guard while experimenting with some chainline stuff on a previous project. 

It never occurred to me before that 104bcd were unlike most 110bcd or 130bcd cranks I have with matching shelf height/spacing on the inner(middle if a triple)& outer ring positions.  My line of thinking was that if the 64bcd 32t position proved to offer better overall alignment than the middle 104mm 32t position I could just shift the bashring to the middle position with some single stack bolts.  Plus it gives me the option of a future 32-48t double for some more road oriented riding but  I was rather surprised to realize the chainguard and OEM outer 44t rings do not actually fit the middle 104bcd position because there's shallower spacing on the shelf to bolt hole on the inside and they'd need to be filed to fit.

This realization had me further wondering about the 48t ring noted as being compatible with my exact 64bcd 32t inner ring for a 2x double crank.  Anywhere I look I only find 48t SRAM/Truvativ rings spec'd as outers and/or for triples with 104bcd (any 48t doubles I've found are a different BCD altogether.)

I'll admit my search hasn't been overly thorough, and possibly even more confusing with the same ring often being labeled as 'SRAM in Truvativ packaging' but for a 32t ring that everywhere I find it clearly states 'for use with 48t' I've yet to find the complementary 48t 'for use with 32t' that would specifically fit as a middle 104bcd.

My moderate investment in this still useful 104/64bcd crank with spare BB-ES51 bottom brackets for both 68mm and 73mm shells and Riv's recent release of the 104/64bcd Silver crank is mostly what has me wondering...

https://planetcyclery.com/sram-32-tooth-64mm-bcd-aluminum-chainring-gray-use-with-48t?gclid=Cj0KCQjwuL_8BRCXARIsAGiC51Cx5-QnwJ5GwH4cASMAgEDJ8yy9wxwkgIGS-zdE3hVNrWIPDNsfh9caAvpcEALw_wcB

You could certainly argue that if I'm ultimately after a narrower 1x chainline and/or 32t/40something double for pavement usage I'd be better off with a narrower q crank, and you'd generally be correct.  I do also have another option with a 110 crank and rings that should be sufficient but just more or less trying to figure out the possibilities and details I've apparently overlooked all these years on 104bcd.

Thanks,

Brian Cole

Lawrenceville NJ

[Joe Bunik]

Colby, ;-)

As a 4-bolt 104mm fan, all I can say is... 🤯

Pics / links would definitely help visualize this - are you saying the "depth" of the shelf for the middle rings is shallower than what is typically seen on other cranks?

I am both excited to learn of the existence of a 48t / 104 as well as the 32t / 64! That could be a game (or really, just a Q-factor) changer...

Thanks
=- Joe Bunik
Walnut Creek, CA

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[Coal Bee Rye Anne]

Hi Joe,

I'll definitely try to get some pics and measurements together.  Unfortunately this is my only 104bcd crank so nothing else to directly compare at this time but I could at least confirm the actual existence of the 32t 64bcd ring.  I'd stumbled on that one a while back and had a LBS order for me and still able to dig that one up from various sites (including the planetcyclery one which was the first one that came up on my last search.) 

And yes, the outer shelf is spaced deeper from the bolt hole than the middle position shelf.  So if I move the middle 32t ring to the outside if floats without contact of the outer shelf but the outer rigns are too deep to fit the shallower middle positin shelf.  This is the first time I've ever seen this detail but also the first time I recall trying to fit an outer 104bcd ring to the middle position so wasn't sure if this crank is just unique or if this design is the same for other 104 cranks. 

[Coal Bee Rye Anne]

Here's a few pics and looks like the total difference is about 1mm in shelf depth.  Last pic is with a Salsa 32t in the outer 104 position with daylight between shelf and bottom of the ring edges.  These sit flush on the shallower middle shelf ledges.

... Scratch that... sorry, corporate seems to have intranet blocks in place keeping me from attaching any photos (yes, this is a much needed distraction from work ; ) and with Google's changes to the mobile side I'm pretty much locked out I guess when it comes to uploading any imagery.  Tried both of our browsers (IE and Chrome( and both paper clip and image attach icons and same restrictions either way.  They've always blocked outside email servers but I was at least able to fully use groups on occasion without issue... up until these recent platform changes.  Bummer.

Joe, I'll be able to send you pics privately but can't share here with the group unfortunately.

Anyway, outer shelf is about 3mm depth from bottom of each bolt hole circumference and inner/middle shelf is about 1mm shallower.  When I place either 32t ring (OEM Shimano 9spd ramped and Salsa 32t non-ramped) in the outer position there's that ~1mm of daylight between the spider shelf ledge and underside of the ring flats.  These same 32t rings sit completely flush on the middle position shelves but that ~1mm is enough of a difference to keep the outside OEM 44t ring and my BBG 32t Bashguard from mounting to the middle position without filing either the underside of ring/guard flats or crank spider shelves.  Not pursuing either of these alterations at this time, however.

Best,

Brian Cole

Lawrenceville NJ

[Victor Hanson]

Brian, 

There is......I have first hand experience.    You cannot mix and match Shimano 10spd chainrings.  Thus, if you a 38 am for the upper ring you must  use a 22 or 24(?) am for the small ring.   So on and forth.   If you mix and match, it will fit together but you will throw the chain between the chain rings.   

This is one advantage of 110mm spiders you can mix and match to your hearts content.   SImilar gearing advantages are achieved through 30/32/34 chainrings and the wide range cassettes now available.   This why SRAM NX Eagle is so popular.  Have fun.  

VTW

On Wed, Oct 21, 2020 at 8:42 AM Coal Bee Rye Anne <lionsrug...@gmail.com> wrote:

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VIctor R. Hanson

Gen Mgr

Schmier Industrial Properties

o:  510-652-0800

c:  510-207-8593

[Jim Plaugher]

Brian, Peter White sells 2 different TA104 chainrings and has pictures and spider dimensions under TA Chinook 9s chainrings. Hope that helps your research!
Jim in Lansing Iowa

[Coal Bee Rye Anne]

Thanks to All who've responded.  I'll definitely be bookmarking the Peter White page and great to know about the TA Chinook ring selection and detailed descriptions. 

Some additional weekend sleuthing yielded some further info and I think I've finally found the 48t mate to my 32t 64bcd ring.  I hadn't realized I had a 10spd ring in my hands and in fact I don't even think the original packaging even specified chain compatability.  But I came across a Bike24 link with some additional searching for SRAM 32-48 combos and this page shows both rings and specified a 2016 model date.

https://www.bike24.com/p2182446.html

I then searched SRAM archived parts calatlogs for 2016 and found on page 92 (last two items) which lists both the 32t and 48t 104bcd which appears to fit as a middle with a longer pin like some of those listed above?

https://www.servicearchive.sram.com/sites/default/files/techdocs/2016_sram_spc_reva.pdf

Glad to know it wasn't just me or an out of spec crank, ha!

Best,

Brian

[Marc Pfister]

The inside shelf is a weird Shimano lock-in thing and it can be easily filed off. 

- Marc