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Thread: Shimano BB92

  1. #1
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    Shimano BB92

    My next XC build I'm going to utilize Shimano's BB92 standard.

    I've searched for shell spec's, but can't find any drawings/info on internal spec's of the shell.
    Even Shimano's tech doc's portion of their website is down...

    I've gleaned info from a few different sources, putting things together... but nothing that looks official. I want to double check with those that have used/built with it to make sure, before getting things done.

    Is it just a straightforward 41.0mm ID x 92mm shell width? Symmetrical, with nothing offset?
    To be faced down to 91.5mm?


    Cheers

  2. #2
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    Search for it by Shimano Press fit.

    http://www.pvdwiki.com/index.php?tit...racket_Options

  3. #3
    pvd
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    For mtb, it's 92mm, offset 2.5mm on the drive side.

  4. #4
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    With people already complaining about external bottom brackets having too high a q-factor, is the BB92 with a 92mm shell only going to make it worse?

  5. #5
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    Quote Originally Posted by bad mechanic
    With people already complaining about external bottom brackets having too high a q-factor, is the BB92 with a 92mm shell only going to make it worse?
    No. You're still using the same Shimano cranks used for outboard bearings. The spindle lengths aren't adjustable, so the Q is exactly the same.
    May the air be filled with tires!

  6. #6
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    Thanks for the info!

  7. #7
    rider of bicycles
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    Digging this one up, to confirm: a BB92 MTN system is made for the same spindle length as a standard 73mm mtb crank, right?

  8. #8
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    It's just the current external style bottom bracket, put back inside an actual BB shell.
    No longer member of the bike industry nor society, so don't hassle me.

  9. #9
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    Thanks, that's what I thought.

  10. #10
    febikes
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    What is the advantage of the new style?

    I think it looks cool but is it lighter and/or stronger then the current threaded BB and external cup style approach using a 73mm shell?

    What I like about 73mm shell vs. 68mm shell is that there is more room for welding on the outside of the stays and it gives an option for a slightly wider tire. This seems to be also an advantage (even more so) with the BB92 style but are there other advantages?

    In terms of downsides other then the new tooling what are the downsides? What happens if after a few years of use, is there a risk that the press in bearing will no longer fit correctly after several years of service?

    -Mark

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    BB92 is a marketing scheme by SHIMANO!!!

    The BB92 is just a press fit bottom bracket. That's it. You don't have to read more. The BB is usually 92mm in length so they called it BB92. Bike companies made their Bottom bracket a little bit narrower, say 89.5 mm so you could put a 2.5mm spacer. When people hear this a the bike shop they think eventually they can buy a one day a crankset that is 89.5. Such thing doesn't exist.

    Oh by the way, you want to know what they were trying to copy. BB30 named for the size of the bearings that are 30 mm not the width. The actual width on a BB30 is narrower therefore giving a better Q factor.

  12. #12
    pvd
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    Silly person.

    BB30 does nothing to alter Q-factor.

  13. #13
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    @Markfarnsworth.

    As far as I can tell BB92 offers no advantages over a threaded bb to the end user. After a mini-nightmare with an On One Whippet I'd go as far as saying BB92 is a deal breaker on any frames I might get in the future.

    It's a pain in the rectum is what it is.

    Of the BB90/92 frames I've worked on so far all have been a pain. None have managed to take a crankset yet without same kind of mod for the cranks.
    Most common (On One Whippet, Trek Madone) problem is small chain rings interfering with the fat BB shell, filing down need to avoid damage. That, is, annoying.
    It also uses the same (too small) size bearings as a normal Hollowtech II bb, so no advantage there either.

    Moreover the primary selling point the BB90/92 is that is allows more area for carbon frames to attach to the shell at the bottom, it doesn't. The ends of the shell have to have clearance for the rings.

    Most irritating of all is that you can only fit Shimmy or Race Face bbs, neither of which are much good compared to Hope (better sealed) and Prestine (tapered roller bearings, last for ages) or any of the other myriad bbs. Fitting and removing them is a pain in the ass too. At the moment my Whippet is fine, but with the way Carbon wears I expect it to be a hive of creaky goodness within a year or two.

    In short, I hate bb92, avoid.

  14. #14
    pvd
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    I've done BB92 on quite a few bikes and there is no reason at all for it to be any different on the crank side than any other system. It must be a manufacturing issue rather than a design issue. Remember that 92mm is asymmetric by 2.5mm.

  15. #15
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    Quote Originally Posted by pvd
    It must be a manufacturing issue rather than a design issue.
    It's a design issue centered around the volume of carbon, or that's my (unskilled) take on it.

    The lay ups on the carbon frames with bb90/92 I've seen/worked on all put a goodly amount of material round the bb insert (assuming there is one). After clear coat that leaves the shell too big to fit 64bcd cranks.

    On a normal HTII bb that's no problem, the inner ring sits over the bb cup, on the bb92 it cuts rings out of the shell. On 2 or 1 ring cranks it's fine, but plenty still want all three.

    The steel bb shell on your wiki is a lot thinner than the carbon ones I'm encountering. That inner ring in the picture wouldn't even fit over the end of the shell on a Whippet. I'd have to file it down so the tabs were flush with the bolts.

  16. #16
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    Quote Originally Posted by markfarnsworth
    What is the advantage of the new style? . . . -Mark
    The advantage is to dazzle you with the over complication of the simple to appear smart

  17. #17
    pvd
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    Quote Originally Posted by Fix the Spade
    That's my (unskilled) take on it.
    Sure enough.

    BB92 does not specify the OD of the BB, just the ID and width. It's a pretty simple standard to work with. The issues you describe are due to poor engineering on the side of the frame manufacturer, not Shimano. That's pretty obvious. Try working with some better brands that do better work and properly engineer their products.

  18. #18
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    Quote Originally Posted by pvd
    Try working with some better brands that do better work and properly engineer their products.
    If I can't trust Trek and On One we're doomed.

    Dooomed!

  19. #19
    pvd
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    Why do you think I started building my own bikes? Nobody else seems to care to much about good design.

  20. #20
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    PVD, since it seems like you are a you are a fan of BB92, can you explain the ream/face required for the job? I noticed your wiki site had a statement about ordering a 1.625 reamer and having it reground. Can you (or anyone else) provide a bit more explanation about the tooling I would need to buy if I decided to go with the BB92?

    After reading this thread and looking at your site I think this is something I would like to try at some point since it seems that it would work well for 29er bikes with short chain stays because it gives more room to weld the stays wide.

  21. #21
    rider of bicycles
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    Quote Originally Posted by pvd
    Why do you think I started building my own bikes? Nobody else seems to care to much about good design.
    I know how you feel. BB92 seems to be a more structurally efficient BB design over a standard threaded 73mm shell to me, which is why I was asking about it.

  22. #22
    pvd
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    You need a 41mm reamer.

  23. #23
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    Joe Bringheli has any sized seatpost reamers made to order foe $150-$210. I'd bet he could have his guy make a 41mm reamer for a bit more.

    http://www.bringheli.com/PDF/TOOLS.pdf
    NOTHING WORKS LIKE CLOCKWORK

    www.clockworkbikes.com

  24. #24
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    Ice toolz do a 41.4mm reamer for 1" zero stack headsets.
    http://www.lifu.biz/icetoolz/index_p...rent=49&id=276
    Should be easy to regrind to 41mm and it'll face the shell as well as ream the ID,
    Once my LBS actually orders me one I'll get it reground and see how well it works.
    Del

  25. #25
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    I know this is an old thread but I am looking to build some frames with the new BB92 standard and I am looking to source a reamer for final assembly. The Ice toolz reamer above has a cutting diameter of 41.4mm, PVD has stated that the ID is 41mm, I can order a 1 5/8" reamer online for cheap and that comes out at 41.275 mm. Wondering if this will work as is given the Ice Toolz specs? Or if I will need to have the 1 5/8" cutter reground to 41mm exactly? Any input would be appreciated.

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