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  1. #1
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    Anybody not impressed with outboard BB bearings?

    I'm not. I built up two frames with outboard BB bearing cranksets. The Shimano XT gives me an actual 50mm chainline. The chain has a tendency to drop from the middle to the granny ring in the rough stuff. The other is a Truvativ Stylo GXP with a 51.5mm chainline (by my measurement). It drops the chain in the smooth stuff.

    I'm going back to Octalink. So I have to replace the BB now and then. It's worth it.

    Or...maybe...1 x 10?
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  2. #2
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    They're fine with a properly adjusted derailleur. I'd try doing that instead.


    If you're still unimpressed I'll take that XT off your hands.

  3. #3
    Never trust a fart
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    Correct chain length and a proper front derailleur setup will stop 99% of your chain drop issues.

    Also, what chain line does your frame call for? Did you try moving spacers around to get it closer to the 47 mm chain line that is a little better?

    Been using external BB's for 3 years now on my personal bikes without issue. .

  4. #4
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    Do you have a spacer on the drive side? You may want to move it to the other side. There is no reason why this spacer HAS TO be on the dirve side, if that's making your chain line off. I swapped it out between drive and non-drive side for my 05 Slayer because the chain line was off with a spacer on the drive side.

    Edit - damn you won.

  5. #5
    ~Disc~Golf~
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    The bearings have nothing to do with dropping chains
    Honestly... ahh I give up

  6. #6
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    Do so! Do so!

    Quote Originally Posted by highdelll
    The bearings have nothing to do with dropping chains
    Ideal chainline is 47.5mm. To make room for the external bearing, the rings are moved outward, changing the chainline to 50mm or more.
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  7. #7
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    Subtle yet unmistable

    Quote Originally Posted by Hardtails Are Better
    They're fine with a properly adjusted derailleur. I'd try doing that instead.


    If you're still unimpressed I'll take that XT off your hands.
    Okay, I'll assume (as you have) that the derailleur is improperly adjusted. Exactly what adjustment are you referring to?

    I'll drop you a PM is I decide to lose the XT. I'm definite going to dump the Stylo, if you're interested in that.
    I dreamed I ate a 10 lb marshmallow. When I awoke, my pillow was gone.

  8. #8
    My gloves stink
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    99%?

    Quote Originally Posted by frdfandc
    Correct chain length and a proper front derailleur setup will stop 99% of your chain drop issues.

    Also, what chain line does your frame call for? Did you try moving spacers around to get it closer to the 47 mm chain line that is a little better?

    Been using external BB's for 3 years now on my personal bikes without issue. .
    Chain length is a short as possible. You're the 2nd guy to mention derailleur adjustment. What specifically are you referring to?

    Both cranksets were installed as per instructions. Neither has any spacers on the drive side.
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  9. #9
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    Quote Originally Posted by Appendage
    Ideal chainline is 47.5mm. To make room for the external bearing, the rings are moved outward, changing the chainline to 50mm or more.
    ....and the spider is inset more than a crank meant for internal bearings...no?

    Plus, when the rear is in the largest cog out back, the chain line is necessarily off and the chain should still not drop.
    Honestly... ahh I give up

  10. #10
    My gloves stink
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    Not entirely

    Quote Originally Posted by highdelll
    ....and the spider is inset more than a crank meant for internal bearings...no?

    Plus, when the rear is in the largest cog out back, the chain line is necessarily off and the chain should still not drop.
    The inset doesn't entirely compensate. That's why 50mm is "normal" now instead of the 47.5mm with the old style. Check it out yourself, all you need is a ruler.
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  11. #11
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by highdelll
    ....and the spider is inset more than a crank meant for internal bearings...no?

    Plus, when the rear is in the largest cog out back, the chain line is necessarily off and the chain should still not drop.
    By definition, the spider is not inset more when the chainline has been moved outboard.

    The more outboard chainline of the crank makes the chain angle more severe when on the larger cogs, which makes it easier for the chain to drop off the rings.
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  12. #12
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    Quote Originally Posted by Appendage
    The inset doesn't entirely compensate. That's why 50mm is "normal" now instead of the 47.5mm with the old style. Check it out yourself, all you need is a ruler.
    I dislike it, too. The new CL "standard" would be better suited to a 150mm rear hub (or a narrower cassette).

    In addition to needing clearance for the bearings, Shimano did this to increase tire/chain/chainring/FD/chainstay clearance.
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  13. #13
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    Quote Originally Posted by Appendage
    ...Check it out yourself, all you need is a ruler.
    yeah...I just measured it and it looks like 53 or so.
    I also think the wider CL also has to do with bigger seat tubes - I had that issue when swapping an old (almost 2 years ago?) ST BB.

    Regardless, I don't drop chains - well VERY rarely
    Honestly... ahh I give up

  14. #14
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by highdelll
    yeah...I just measured it and it looks like 53 or so.
    I also think the wider CL also has to do with bigger seat tubes - I had that issue when swapping an old (almost 2 years ago?) ST BB.

    Regardless, I don't drop chains - well VERY rarely
    The seat tube is not a factor
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  15. #15
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    Quote Originally Posted by shiggy
    The seat tube is not a factor
    yeah it is...It puts the derailleur out further.
    Front Derailleur Chain Rub W/Pics
    Honestly... ahh I give up

  16. #16
    the catalan connection
    Reputation: What&son's Avatar
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    This is my recently built new crankset.
    Q factor 163, chainline 47.5
    Attached Thumbnails Attached Thumbnails Anybody not impressed with outboard BB bearings?-prova-fotos-y-videos-nokia-011.jpg  

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  17. #17
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by highdelll
    yeah it is...It puts the derailleur out further.
    Front Derailleur Chain Rub W/Pics
    The seat tube is not the issue. You were using a FD designed for the new, outboard, chainline on a crank with the old chainline. Its working range is further out regardless of the seat tube size it is mounted on.

    Shimano designed the new FD to not swing inward as far. You would have had the same issue if you had mounted the new FD on your old frame.
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  18. #18
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    Quote Originally Posted by shiggy
    The seat tube is not the issue. You were using a FD designed for the new, outboard, chainline on a crank with the old chainline. Its working range is further out regardless of the seat tube size it is mounted on.

    Shimano designed the new FD to not swing inward as far. You would have had the same issue if you had mounted the new FD on your old frame.
    I get that - but the reason I had to get that derailleur was because of the seat tube size
    Honestly... ahh I give up

  19. #19
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    Problem solved, probably

    I think I've solved the problem on the bike with the XT crankset and 68mm BB shell. The installation instructions call for two 2.5mm spacers on the drive side and one on the non-drive side, which is how I installed it, and which gave me the 50mm CL. So I took one of the driveline spacers and put it on the non-drive side. Measured the CL, it is 47.5mm. Took the bike for a good 2-hour trashing in rough terrain and based on that ride my preliminary conclusion is that the problem is reduced if not resolved entirely.

    My other bike has a 73mm shell so I don't have the luxury of moving spacers around. Maybe if I dumped the 51.5mm CL GXP crank and replaced it with a 50mm CL set I'd be okay. But I'll be giving Octalink a try on that bike once all the stuff arrives.

    I don't know what all this says about the "modern 50mm chainline" except that I no likey.
    I dreamed I ate a 10 lb marshmallow. When I awoke, my pillow was gone.

  20. #20
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    I never knew that external setups have a different chain line. I also thought anywhere between 47.5 and 50 was acceptable, not 47.5 = internal, 50 = external.

    To the OP - I'm not sure I entirely understand though. You swapped bottom brackets entirely? From 73 to 68? Is that even possible? I thought if you had a 73, you use 73, if you had 68, you use 68, etc.

    Side Question - Is there any sort of strength difference between the 73 to 68mm bottom brackets? Given all things equal, of course. (I couldn't help but to notice a good portion of full sus bikes have 68mm shells...)

  21. #21
    the catalan connection
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    External shimano BB come with 3 spacers of 2.5mm. If you have a 68mm bb shell on your frame you mount 2 on the drive side (if not a e-type derailleur) and one on the non drive. If you have a 73mm BB shell you mount only the drive side spacer (again if not on e-type derailleur, in wich case the derailleur plate takes the spacer place).
    Some people mount the drive side spacer to the non drive for getting a better chainline, but that means youŽll have an off center crankset. Some people donŽt mind. I do.
    Answering your question, the crankset spindle either fits a 68 or a 73 BB shell, so no strength difference here. But a 73 mm BB shell will get more BB cup insert so there is some advantage here, but sure is marginal.
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  22. #22
    g3h6o3
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    Quote Originally Posted by Appendage
    I think I've solved the problem on the bike with the XT crankset and 68mm BB shell. The installation instructions call for two 2.5mm spacers on the drive side and one on the non-drive side, which is how I installed it, and which gave me the 50mm CL. So I took one of the driveline spacers and put it on the non-drive side. Measured the CL, it is 47.5mm. Took the bike for a good 2-hour trashing in rough terrain and based on that ride my preliminary conclusion is that the problem is reduced if not resolved entirely.

    My other bike has a 73mm shell so I don't have the luxury of moving spacers around. Maybe if I dumped the 51.5mm CL GXP crank and replaced it with a 50mm CL set I'd be okay. But I'll be giving Octalink a try on that bike once all the stuff arrives.

    I don't know what all this says about the "modern 50mm chainline" except that I no likey.
    Or, you could get a road BB that has only 1 spacer, thus 47.5mm CL.
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  23. #23
    g3h6o3
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    As far as the OP's question, I'm not impressed about wear on Ex. BB. They simply do not last more than a season or two, it's a shame!
    Check out my SportTracks plugins for some training aid software.

  24. #24
    My gloves stink
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    Quote Originally Posted by Roasted
    I never knew that external setups have a different chain line. I also thought anywhere between 47.5 and 50 was acceptable, not 47.5 = internal, 50 = external.

    To the OP - I'm not sure I entirely understand though. You swapped bottom brackets entirely? From 73 to 68? Is that even possible? I thought if you had a 73, you use 73, if you had 68, you use 68, etc.

    Side Question - Is there any sort of strength difference between the 73 to 68mm bottom brackets? Given all things equal, of course. (I couldn't help but to notice a good portion of full sus bikes have 68mm shells...)
    CL on an old style internal BB depends on spindle length. 113mm spindle should give you a 47.5mm CL which was standard. Other spindle lengths are available for other setups, although I don't know what. Maybe someone on here knows that.

    A current external bearing Shimano, installed per instructions, will give you a 50mm CL. As stated earlier, my Truvativ Style crankset and BB, installed per instructions, gave me a 51.5mm CL. Ext bearing BB's come with spacers so that you can use the same BB with either a 68mm shell or 73mm shell.

    The correct CL is the one that works for you. Plenty of people chimed in here saying 50mm works for them. I haven't been that lucky.
    I dreamed I ate a 10 lb marshmallow. When I awoke, my pillow was gone.

  25. #25
    My gloves stink
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    Off-center crankset

    Quote Originally Posted by What&son
    Some people mount the drive side spacer to the non drive for getting a better chainline, but that means youŽll have an off center crankset. Some people donŽt mind. I do.
    Wow, I didn't even think of the offset-center issue. When I rode the bike yesterday, I didn't even notice it!
    I dreamed I ate a 10 lb marshmallow. When I awoke, my pillow was gone.

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