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Thread: Crank choice

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    Crank choice

    I am planning to build another tandem from the frame up soon,and I'm trying to decide on a crankset. Square taper offers the option of different spindle lengths to optimize the Q/chainline/clearance/etc,but BB's are getting harder to find. I know Phil Wood is out there,but this expense makes it a somewhat more difficult choice.

    The FSA Mega Exo seems attractive,but there are no choices in spindle length,so clearance may be an issue. Does anybody know of clearance issues with these cranksets on modern frames?The frame will not be a Santana,so 160 is not an issue.Most likely it will be a Cannondale or Co-Mo. Any reports on how the mega Exo BB's are holding up? I have chasing/facing tools,so BB prep will be good.

    ISIS is not a consideration,nor Octalink.It seems that the industry has made something of a mess out of the BB area of modern bikes...

    dan
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    hors category TandemGeek's Avatar
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    Quote Originally Posted by dfcas
    It seems that the industry has made something of a mess out of the BB area of modern bikes...
    Actually, I'm pretty sure the industry has been making a mess out of the bottom bracket area as long as there have been bottom brackets, e.g., British Standard (BSA), English, French, Swiss, Italian, ISO vs JIS square tapers, ISIS, Octalink, ISIS II, Gigapipe, etc... What a mess.

    This past weekend was my first close-encounter with FSA's highly integrated SL-K MegaExo BB & crankset. Although they cite a 46mm chain line, the ones I was looking at looked more narrow than that and a quick check of the outer chain ring orientation confirmed that they were indeed "tight in" on the frame, e.g., ~50mm? While everything seemed cozy, there wasn't an interference problem at the chainstays; however, the ubiquitous "chain chatter" against the big chain ring that often exists on tandems when attempting to run in the smallest cogs from the middle chain ring position was alive and well.

    I've sent off a question to someone who I believe would be well positioned to know how the MegaExo / Shimano 10spd on 145mm tandems is working and hope to hear back in a week or so. It's quite possible that summer vacations may be pulling folks out of their offices given the time of year. If there are any epiphanies I'll pass them along. Otherwise, I too am interested in hearing how the latest and greatest tandem cranksets are working out.

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    MegaExo on Co-Motion

    We are running the MegaExo on a 2005 Co-Motion Supremo with 54-42-30 rings and an 11-23 Campy cassette. Properly adjusted, we have no problems with interference running the 42/11 combination. We also run a 48-38-26 with a 13-29 with no problems. So far, we have over 5000 miles on the bike with no issues with the crankset other than a changeout on the big ring as a result of wear.

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    Quote Originally Posted by Senojev
    We are running the MegaExo on a 2005 Co-Motion Supremo with 54-42-30 rings and an 11-23 Campy cassette. Properly adjusted, we have no problems with interference running the 42/11 combination. We also run a 48-38-26 with a 13-29 with no problems. So far, we have over 5000 miles on the bike with no issues with the crankset other than a changeout on the big ring as a result of wear.
    What's the chainline measure out to on your Supremo, i.e., center of frame to center of middle chain ring?

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    Chainline on Supremo

    TandemGeek:

    The best measurement I could get shows the chainline to be 47mm. Hope this helps.

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    hors category TandemGeek's Avatar
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    Quote Originally Posted by Senojev
    TandemGeek:

    The best measurement I could get shows the chainline to be 47mm. Hope this helps.
    Are you using a C-10, KMC X-10, or Shimano chain?
    Last edited by TandemGeek; 06-07-07 at 06:54 AM.

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    Cyclist, Inline SpeedSk8r Sk8erByker's Avatar
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    We are running the FSA's SL-K MegaExo BB & cranks, Rotor Q-Rings, with Dura-Ace 10-sp & SRAM chain, on our 2006 CoMo Supremo. Our chainline is indeed 46mm. We have no interference with the stays, but do get chatter while in the 42/11 & 12 combos. Prior to installing the Q-Rings, we got the chatter only slightly, and only while in the 42/11.
    Charlie & Pat

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    Chain

    TandemGeek:

    We are running a C-10 chain on the Supremo.

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    Senior Member pocky's Avatar
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    Quote Originally Posted by dfcas
    Square taper offers the option of different spindle lengths to optimize the Q/chainline/clearance/etc,but BB's are getting harder to find.
    Are they really getting harder to find, or is their percentage in the market just getting smaller because the industry has flooded us with tons of different interfaces right now, instead of two or three? If you bike around remote corners of the world and bust a bottom bracket or crank, you'll have a far easier time finding a square taper one.

    Nashbar lists FIFTEEN different choices for square taper BB's, including four in its house brand, ten in Shimano (5 different spindle lengths for 68mm!), and one in Campagnolo, versus eight choices for ISIS and four for Octalink.

    See this thread: http://bikeforums.net/showthread.php?t=290371
    The only really convincing reason I've seen to ditch square taper is ease of disassembly, which for a tandem, could be a very good reason.

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    hors category TandemGeek's Avatar
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    Quote Originally Posted by pocky
    The only really convincing reason I've seen to ditch square taper is ease of disassembly, which for a tandem, could be a very good reason.
    Can you elaborate as I'm not sure I fully comprehend the inference, i.e., do you mean that square tapers are too hard or too easy to disassemble?

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    Senior Member pocky's Avatar
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    Quote Originally Posted by TandemGeek
    Can you elaborate as I'm not sure I fully comprehend the inference, i.e., do you mean that square tapers are too hard or too easy to disassemble?
    I meant that square tapers are harder to disassemble than a splined or integrated interface (especially a pullerless one-key-release system type), presumably due to the greaseless "stretch the hole" physics of the square interface. Stripping the crank threads even if everything's threaded properly is a concern with the square taper crank puller. Because the principle of the crank attachment mechanism in the splined or integrated systems isn't about deformation of the aluminum of the crank hole itself, it should come off easier. So if you frequently remove and reinstall your cranks, I imagine the splined or integrated systems might save you a bit of hassle. Then again, I suspect the hassle of trying to replace a proprietary system in the middle of nowhere could be worse.

    Also, Sheldon points out that repeated removal and reinstallation of square taper cranks does in fact enlarge the hole, causing your chainline to decrease a miniscule amount over time, and this could theoretically cause you to eventually bump into the edge of the taper if you're mixing JIS and ISO standard tapers. But he says he's done this a lot and he's never seen it happen. This is interesting from a purely scientific perspective but I don't think it's any sort of a valid argument against the square taper.
    http://sheldonbrown.com/bbtaper.html
    Last edited by pocky; 06-08-07 at 01:13 AM.

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    Quote Originally Posted by pocky
    I meant that square tapers are harder to disassemble than a splined or integrated interface ... This is interesting from a purely scientific perspective but I don't think it's any sort of a valid argument against the square taper.
    No offense, but you're talking in circles.

    My sense here is, you're simply regurgitating what Sheldon has written to educate cyclists coupled with the marketing BS that was put forward to support the acceptance of new-fangled, licensed and sometimes proprietary splined interface designs. Similar "technical discussions" have supported increases in head tube diameters, larger crank BCDs (and more recently smaller, "compact" BCDs), lower spoke count wheels, every different type of frame material, 29" wheels for off-road use, and so on.

    Here's the deal: A square taper is no different than any other component on a bicycle. It requires a certain amount of knowledge to properly spec. (ref. to JIS & ISO) and to service, to include understanding torque specifications and the like. Just as square tapers can be over-torqued by a novice, splined interfaces can be incorrectly aligned and/or also incorrectly torqued. Moreover, the use of self-extracting crank bolts eliminates the need for a crank-puller to facilitate quick and easy removal and reinstallation of square taper cranks (I've used them for well over a decade).

    Bottom Line: With few exceptions, square tapers are more than adequate for the vast majority of cyclists. They have few REAL drawbacks for all but the strongest cyclists who have a compelling reason to eliminate all forms of drivetrain deflection, e.g., professional racers. Splined interfaces are a bit more idiot proof and help to preclude so-called "bike shop techs" or do-it-yourselfers from deforming square taper cranks by over-torquing during installation which may or may not be a good thing, i.e., it allows their lack of skill to go unnoticed a little bit longer similar to how threadless headsets no longer require as much "touch" to properly adjust compared to the older quill models. Good and skilled mechanics are a dying breed.
    Last edited by TandemGeek; 06-08-07 at 05:30 AM.

  13. #13
    Senior Member pocky's Avatar
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    Quote Originally Posted by TandemGeek
    No offense, but you're talking in circles.
    None taken! I have square taper on all my bikes. Besides, you're a very knowledgeable fellow and I don't mind the criticism. For everything you just wrote in your last post, I came to the same conclusions so I agree with you completely: I was just playing devil's advocate for the one solitary point I had read on another thread (can't find it now) in favor of splined for average cyclists that seemed to make sense--getting the greased splined crank off would be easier and require fewer tools than the average square, for users that might remove and reinstall their cranks all the time for portability. I don't fall into that category, so I don't care. But it sounds from what you're saying that square with one-key-release bolts is pretty quick too. (I've never used 'em; I suppose I would if I found myself packing and unpacking cranks a lot.)
    Last edited by pocky; 06-08-07 at 10:08 AM.

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