Chain-Length on GX Eagle?- Mtbr.com
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  1. #1
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    New question here. Chain-Length on GX Eagle?

    Setting up my new bike. What's the best way to size the chain for a setup like this? In day's past, I'd just "eyeball" it. But with a 12 speed, and on a brand new bike, I don't really have a "feel" for anything yet.

    Also the adjustment that pushes the detailer towards and away from the cassette.... I saw one SRAM video where they had a nice gauge tool for that. But being a normal person without that gauge, is there some other way to adjust it? It looks like you should be able to use a normal measuring device to pretty accurately get the center point of the pulley the right distance from the big cog... but what is that distance?
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  2. #2
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    You wrap the chain around the chainring and largest cassette cog and add 4 links for full suspension bikes (with suspension fully compressed) or 2 links for a hardtail. Once routed through the derailleur the length will be right.
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  3. #3
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    4 links for the hardtail, 2 for the full suspension. Seems backwards, but that's what's in the manual.
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    Quote Originally Posted by briantortilla View Post
    4 links for the hardtail, 2 for the full suspension. Seems backwards, but that's whats in the manual.

    Yes, that's what I meant to write but got it backwards.
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  5. #5
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    If you don't have SRAM instructions get them and follow them for derailleur setup...website also has a good video. The 'B-gap' tool is useful but you can use a small metric ruler. The 'gap' is 15mm from top of upper jockey wheel to bottom of biggest cog on cassette with susp compressed.

    Park tool site has good videos on proper chain sizing
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  6. #6
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    I tend to agree with that, think SRAM somehow fvcked up on that one and got it backwards as well. Why would a HT, which has no chain growth need a longer chain vs a FS which can have lots of chain growth Definitely follow their instructions for the B-screw adjustment though, quite critical.


    Quote Originally Posted by briantortilla View Post
    4 links for the hardtail, 2 for the full suspension. Seems backwards, but that's what's in the manual.
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  7. #7
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    Quote Originally Posted by LyNx View Post
    I tend to agree with that, think SRAM somehow fvcked up on that one and got it backwards as well. Why would a HT, which has no chain growth need a longer chain vs a FS which can have lots of chain growth Definitely follow their instructions for the B-screw adjustment though, quite critical.

    It's probably because you're not usually riding with the suspension maxxed out so if you size it +4 it wouldn't be optimal when in the normal range of travel. I doubt SRAM got it wrong and for sure I would follow their instructions.
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  8. #8
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    The SRAM directions are indeed correct. On a FS bike you need to compress the shock to the point of MAX chain growth, and then measure the chain and add two links. This means when the suspension is not compressed and there is less chain growth, you will have MORE than 2 links overlapped. It will probably be closer to 4 links overlap when uncompressed, depending on your suspension. The important thing is that you measure at MAX chain growth, that way the chain can never be pulled any tighter by suspension travel.

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    Here it is, visual representation
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  10. #10
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    I put the chain on full length, and then removed one link and test fitted, removed another link etc... until it fit right.
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    Quote Originally Posted by davesupra View Post
    I put the chain on full length, and then removed one link and test fitted, removed another link etc... until it fit right.
    I agree that's the most foolproof way for the home mechanic who isn't trying to save a couple minutes.
    And it'll let you see what the shortest possible chain you can get away with is.

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    Quote Originally Posted by ac1000 View Post
    I agree that's the most foolproof way for the home mechanic who isn't trying to save a couple minutes.
    And it'll let you see what the shortest possible chain you can get away with is.

    You'd be better off sizing it correctly, the shortest possible chain you can get away with isn't always the best. You could remove 2 links at a time until you get there but it seems like it's easier just to do it once. Just my opinion.
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  13. #13
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    get the b tension tool and follow the sram instructions. If you do not setup eagle right it will not only never perform correctly but you risk derailleur destruction. eagle isn't forgiving with setup, you either do it right and it's the best drive train you've ever owned, or you don't and you hate it. Read the entire eagle thread in this sub forum for context.

    For reference, there is plenty of info on the question you asked in that thread already. There was no need for a new thread.

  14. #14
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    Quote Originally Posted by J.B. Weld View Post
    You'd be better off sizing it correctly, the shortest possible chain you can get away with isn't always the best.
    Could you explain how the shortest possible chain is not necessary the best?
    Not disagreeing with you, just hoping to learn more.

  15. #15
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    Unnessesary strain on the drive train by maxing out the derailleur travel when on the biggest cog. A bad landing, hammering hard enough to flex too much and there goes the chain, derailleur or cassette

    And SRAM screwed up instructions big time. Probably the cause of all the early reports of bent 50t cogs.

    Doesnt matter what drivetrain. Eagle or shimano 1x10. Its big ring big cog and plus 2 links. For full suspension you compress to max chain growth then big, big plus 2 links.

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  16. #16
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    Quote Originally Posted by ac1000 View Post
    Could you explain how the shortest possible chain is not necessary the best?
    Not disagreeing with you, just hoping to learn more.

    Basically what RAKC said, you can size a chain so it can still shift into the big cassette cog but be unnecessarily tight which stresses the derailleur, which is why the instructions have you add a little beyond what might be technically the minimum.
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  17. #17
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    I had a full suspension single speed (IGH) setup for a while, and the chain was too short. Near the bottom of the travel, it would run out of chain and thump like it was hitting something solid, but it was just the lack of more chain. Somehow I never broke it, and once i figured it out, I put a link back.
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  18. #18
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    Quote Originally Posted by RAKC Ind View Post
    And SRAM screwed up instructions big time.

    Why do you think that? If their instructions were an error that was costing them warranties and reputation I think they'd make a revision. The instructions basically say what you said, big/big +2 with the suspension at full growth. They do ask for more chain (big/big + 4 links) on a hardtail but that would put less stress on the 50t.
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  19. #19
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    I didnt see the part about at full growth. I dont have Eagle (far from worth the money imo) and seemed like from the convo here something wasnt right about the instructions.

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  20. #20
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    Quote Originally Posted by RAKC Ind View Post
    I didnt see the part about at full growth. I dont have Eagle (far from worth the money imo) and seemed like from the convo here something wasnt right about the instructions.

    Sent from my SM-G950U using Tapatalk

    I think there is some confusion as to why they ask for +2 links on full suspension and +4 links on a hardtail because it seems like it might be the opposite, but after thinking about it that makes sense to me now.
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  21. #21
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    why not err on the longer side? dropped chains on a narrow wide/clutch combo are rareer than flats on a tubeless setup.

  22. #22
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    Quote Originally Posted by ElwoodT View Post
    why not err on the longer side? dropped chains on a narrow wide/clutch combo are rareer than flats on a tubeless setup.
    I agree, slightly long beats slightly too short.
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    Quote Originally Posted by ElwoodT View Post
    why not err on the longer side? dropped chains on a narrow wide/clutch combo are rareer than flats on a tubeless setup.
    I had both, well almost, in the same ride today.

    Not sure how, but actually dropped a chain for the first time, just shifted to my granny ring and somehow dropped the chain. Nothing is worn, chain is new, not sure I didnt kick up a stick or catch it with the heal of my shoe. About 1/2 mile later, for the first time ever I punctured my tire to the point it hissed for a bit before finally sealing. Didnt loose enough pressure to be a huge deal since the rough stuff was over, avoided wasting a CO2.

    In fairness was an advanced blue loop that hadnt been ridden really and not cleared from off season down fall as trails just opened a few days ago. And that was only a 2 mile loop of a 12 mile total trail set...

    So ya my luck is THAT bad lol.

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  24. #24
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    Quote Originally Posted by J.B. Weld View Post
    Basically what RAKC said, you can size a chain so it can still shift into the big cassette cog but be unnecessarily tight which stresses the derailleur, which is why the instructions have you add a little beyond what might be technically the minimum.
    I don't we disagree on that point. If you are stressing the derailleur I think you can see that visually when in the largest cogs and the suspension compressed to the longest point of chain growth.

    Next time I'll try it your way but I'll still check it to see if I was on the cusp of taking out 1 more link without stressing out mr. derailleur.

  25. #25
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    Quote Originally Posted by RAKC Ind View Post
    I didnt see the part about at full growth. I dont have Eagle (far from worth the money imo) and seemed like from the convo here something wasnt right about the instructions.

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    Seems odd to comment on how to set up a drivetrain you don't have. Also regarding not worth the money... it's not as if GX eagle is significantly more expensive then an XT drive train. But when I see comments like yours the first thing I think is... this person doesn't do long hauls in the mountains.

    If you're doing 20-50 mile rides with 4-7k elevation with climbs that last for 30-40 minutes... eagle is worth every single penny and then some. Especially true because you can get an extra climbing gear for 12-17% grades without compromising the antisquat design kinematics of your frame.

  26. #26
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    Quote Originally Posted by ac1000 View Post
    I don't we disagree on that point. If you are stressing the derailleur I think you can see that visually when in the largest cogs and the suspension compressed to the longest point of chain growth.

    Next time I'll try it your way but I'll still check it to see if I was on the cusp of taking out 1 more link without stressing out mr. derailleur.
    It's entirely possible to size a chain that works, but would be more optimal with 2 more links, which is why I said that "the shortest possible chain" isn't necessarily the best.

    I think that following the manufactures directions is the easiest and best method.
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  27. #27
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    Quote Originally Posted by sturge View Post
    If you don't have SRAM instructions get them and follow them for derailleur setup...website also has a good video. The 'B-gap' tool is useful but you can use a small metric ruler. The 'gap' is 15mm from top of upper jockey wheel to bottom of biggest cog on cassette with susp compressed.

    Park tool site has good videos on proper chain sizing
    So you measure from the tip of each tooth to get the 15mm distance? Or inbtween 2 teeth on the upper jockey to the tip of one of the teeth on the cassette.

  28. #28
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    Quote Originally Posted by minimusprime View Post
    Seems odd to comment on how to set up a drivetrain you don't have. Also regarding not worth the money... it's not as if GX eagle is significantly more expensive then an XT drive train. But when I see comments like yours the first thing I think is... this person doesn't do long hauls in the mountains.

    If you're doing 20-50 mile rides with 4-7k elevation with climbs that last for 30-40 minutes... eagle is worth every single penny and then some. Especially true because you can get an extra climbing gear for 12-17% grades without compromising the antisquat design kinematics of your frame.
    Agreed. Gotta wonder sometimes. I just installed a 12 speed drivetrain on my cheapo Surly Karate Monkey and the upgrade cost me $300 in parts, $35 for a new 12 speed chain tool (Park CT 3.2), some spare cable and housing I have sitting around, $13 for a 4 pack of spare quick links, and some time. The use of the b gap tool was surprisingly useful. Had to put a 12 speed ring on the stock NX crankset and that was good to go. A tooth broke off the stock 11 speed cassette on the 11t cog after 3,000 miles on it. 11-41t was nice, 11-50t is way better. I do 15-100 miles per day on this bike since it's my bikepacking and singletrack bike.

    I cut my chain per the Sram instructions in their video - which specifically states for hardtails 2 inner links and 2 outer links, for full suspension 1 inner link and 1 outer link from where the overlap starts.

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