1. The most important thing about buying a new bike is to make sure it fits. The only way you'll know if the bike is right for you is to size up the bike and make sure that the bike's geometry matches your body's geometry. Ask questions and do some research.
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2. If possible, try to find a shop that will let you demo the bike on real dirt. Five minutes in a parking lot won't cut it. You wouldn't buy a car without a real world test drive, and a bike should be no different.
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  1. #1
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    Need help understanding BB and Crank

    Hello All,

    I'm suffering from a total lack of knowledge for bb and cranks. I've been picking most things up but this is proving a little difficult for me. Way too much information out there.

    I have a 2012 Trek Marlin which I've been upgrading over the past two seasons. Trek Bicycle

    I want to upgrade the drivetrain and go to a 1x10. I'm not in a rush and am just snagging the best deals as they come along. I already have a 1x10 Shimano Deore Shifter so I will get a shimano derailleur eventually. I have a pretty good understanding of the cassette, deraillieur, chain, and shifters working together but i'm lost with the cranks and bottom brackets.

    I know my bike has a square tapered bb and the cranks are not usesable b/c they are one piece with the chainrings.

    What size/style bottom bracket do I need or can I use/not use?

    When looking at cranks I see some that 1x10 specific. Can i use a 2x10 crank and drop the granny off? Could I use a ss crank and replace the chainring with a 10spd ring?

    If i use a regular chainring (not a narrow wide) than I have to use a chain guide correct?

    Thanks in advance for any advice

  2. #2
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    I'm also a little confused about Shimano's Dyna-sys if anyone has pointers for that as well. Are all shimano 10 speed components compatible with each other or are some 10spd products dyna-sys and some aren't?

  3. #3
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    partial advice:

    get a single-speed specific crankset with the appropriate BB. (a SS ring does not mean that it's only for single-speed use, just single front chainring use.) remove the current crankset and BB and sell/give them away together. there are lots of SS-specific cranksets out there and most of them will have a 32t or 33t chainring.

    there are a lot of newer chainrings out there with a unique tooth shape that are designed to not drop the chain. these are a great idea, but if you can't get a "no drop" chainring, get some sort of chain guide to help avoid dropping. I have been using a MRP guide- Mountain Racing Products home of MRP, White Brothers, Kreitler, Tamer, and Power Grips | 1x

    I think one of the new Shimano Shadow Plus derailleurs with the clutch is worth the extra money, especially for a 1x drivetrain.

  4. #4
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    Thanks. I have heard that as well. Which ones have the clutch. I never see it come up in the specs?

    Aren't the chainrings speed specific though? I just assumed a single speed ring was for a wider chain then a 10spd?

  5. #5
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    Read this article:
    Bottom Bracket Types - Your Complete Guide To Threaded, BB30, BB90, BB95, BB386 EVO, BBright, PF86 And PF92 - BikeRadar

    This is the bottom bracket that you have...
    Halfords | VP-BC73 68 x 122.5 Square Taper Cartridge Bottom Bracket

    You can use conventional threaded bottom brackets to replace the one you currently have.

    This is from the article above about threaded bottom brackets:
    Pros: Easy at-home service; interface surfaces can often be machined; huge selection of parts and accessories
    Cons: Heavier than press-fit systems; frame design limited by relatively small-diameter and narrow shell
    Crank designs that will fit: Standard 24mm external type (Shimano Hollowtech II, SRAM/Truvativ GXP, Campagnolo Ultra-Torque, FSA MegaExo, Race Face X-Type, etc), square taper, ISIS, BB386 EVO

  6. #6
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    Thank you very much. That helps to understand some of the differences but i'm still confused by some of the specs I see when looking at them online. For example I dont understand what the 68/73mm or 83mm or external cup specs mean.

    Do they have to correspond to the cranks i want to use or the frame i have?

  7. #7
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    The measurements refer to the width of the frame where the bottom bracket goes.

  8. #8
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    Ok, I'm now seeing that its shell width? So do you know how i can find out what size shell i need? Or do i have to pull mine out and measure it?

  9. #9
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    nevermind, i'm guessing that is in the link you sent from my bb. so i should be looking for a bb with a 68mm shell width. Can I do 68/73?

    Thanks for baring with me

  10. #10
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    Quote Originally Posted by hankscorpio View Post
    Thanks. I have heard that as well. Which ones have the clutch. I never see it come up in the specs?

    Aren't the chainrings speed specific though? I just assumed a single speed ring was for a wider chain then a 10spd?
    there's Shadow and Shadow Plus. the "plus" is the clutch that eliminates chain slack/slap.

    chainrings for 3x or 2x setups are designed to allow the chain to pop off the ring when you shift. they have gates and pins to aid in shifting. a SS ring has taller teeth and lacks the ramps and pins. a "shifting" chainring will be more likely to drop the chain when you don't want it to, whereas a SS chainring will be more likely to hold the chain.

    most SS rings have narrow teeth that will work with any chain. some are extra thick for a 1/8" SS chain, but there's no real need for that. most SS riders seem to use narrow SS chains or 8-speed chains.

    Quote Originally Posted by hankscorpio View Post
    nevermind, i'm guessing that is in the link you sent from my bb. so i should be looking for a bb with a 68mm shell width.
    if you buy a new crankset and want to use your old BB, find out what length spindle you need for the new cranks. your frame likely has a standard 68mm shell (check the specs on that first).

    this Shimano cranks, it's pretty easy to find out what you have. locate the model number of your cranks, it should be something like "FC-M311" or something. do an internet search for "shimano FC-M311 PDF" with whatever model number you have. you will easily find a PDF document on Shimano's website like this one: tech doc, which tells me that, for example, you need a 123mm BB with the FC-m311. if the crankset you have now takes a much wider or narrower BB spindle, it will be difficult to get the chainline to work.

  11. #11
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    Quote Originally Posted by hankscorpio View Post
    nevermind, i'm guessing that is in the link you sent from my bb. so i should be looking for a bb with a 68mm shell width. Can I do 68/73?

    Thanks for baring with me
    68/73 is probably what you are looking for.

    Also, you don't necessarily need a shadow + (clutch type) Rear Der.

    When using the Narrow Wide ring, its not required, though it does help with chain slap.

  12. #12
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    You guys are awesome, thanks. It looks like I need something that is 68/73 and 123mm bb

  13. #13
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    why do you need a 123mm BB? what crankset are you putting on this bike?

    the length of the BB will determine your chainline, ie, how far the chainring (the center chainring if it's a triple, or the center of the two chainrings if it's a double) is from the center of the frame. depending on the design of the crank arm, the appropriate spindle can vary by several millimeters, so choosing the right spindle is critical. or it's at least critical to get it close enough to work, within 3mm or so. some cranks work best with a 118mm spindle, others need a 126mm spindle, and so on. the best way to know is to research what the manufacturer suggests. I am sure there is some way to measure it and find the right one arithmetically, or by trial and error, but it's usually easier to just look up what the manufacturer recommends.

  14. #14
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    yea I'm still confused and finding that most cranksets online dont tell you the spindle length.

  15. #15
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    Many cranksets will include this info. Take this SLX crankset for example. This one actually notes that includes the external bearing BB cupset, and will supply the spacers needed to accomodate either a 68 or 73mm shell.

    If I were in your spot, I'd consider this crank. Price is right, includes BB, and can convert to 1x10 easily.. Info here on how the spacers work with an External Bearing BB and BB shell size to create the appropriate chain line Park Tool Co. ParkTool Blog External Bearing Crank Systems (Hollowtech II, MegaeXo, Giga X Pipe, X-type, Campagnolo Ultra Torque)

  16. #16
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    Thanks a lot. I had once heard that 2x10 setups didn't convert as well as a triple or single because of the chainline?

  17. #17
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    Race Face Evolve SS Cranks 2012 Oe > Components > Drivetrain > Cranksets | Jenson USA Online Bike Shop
    Race Face Ride Single Speed Cranks 2013 > Components > Drivetrain > Cranksets | Jenson USA Online Bike Shop

    Something like this that uses an external bottom bracket. As long as its not 83mm you should be fine. The description sounds like it comes with a bb, but I am not sure. Also, Ebay has great deals on take off cranksets.

  18. #18
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    Quote Originally Posted by hankscorpio View Post
    Thanks a lot. I had once heard that 2x10 setups didn't convert as well as a triple or single because of the chainline?
    Seems to me that it shouldn't be a problem with one of the new narrow/wide rings. The chainring will be on the 104bcd position of the crankset, which would be the same as where the "big ring" would be with the 2x10 setup. However I have no direct experience with that conversion.

  19. #19
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    This doesn't have anything about BBs, but I used this guide to help me when I converted from 3X10 to 1X10.
    Trail Tech: Put Your Drivetrain On A Diet - BikeRadar

    I went with the WolfTooth components chainring, but RaceFace's looks good too.

  20. #20
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    Great link! +1

  21. #21
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    I actually did a live chat with Jenson yesterday about that specific set you linked and it does come with a bb. Thanks again everyone. As i've learned about components over the last year bb have proven to be the most confusing in terms of fit

  22. #22
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    Quote Originally Posted by hankscorpio View Post
    yea I'm still confused and finding that most cranksets online dont tell you the spindle length.
    they do if you know how to look. SRAM/Truvativ should have all that tech info on their website. Shimano makes it painfully easy to find.

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