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  1. #1
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    What does "B.C.D" mean for chainwheels?

    This is a dumb question but I didn't see it on the Sheldon Brown site and I want to order a replacement chainwheel. Thanks!

  2. #2
    Dharma Dog lhbernhardt's Avatar
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    Bolt Circle Diameter. If you scribed a circle around your cranks, with the center at the middle of the bb axle and the circumference passing thru the center of all the bolt holes of the chainring, the diameter of that circle would be the bcd.

    Standard road (and track) bcds:

    Shimano road: 130mm

    Campag road: 135mm

    Standard track (also Campag Nuovo Record road, back in the 70's): 144mm

    Old style Campag (going way back): 151mm (figure that one out!)

    Compact cranks: 110mm

    Luis

  3. #3
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    Thank you, Luis!

  4. #4
    Life is good RonH's Avatar
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    Sheldon Brown has all the details with pics.
    Here you go. http://sheldonbrown.com/gloss_bo-z.html#bcd

  5. #5
    Semper Fi USMC qcpmsame's Avatar
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    In the same vein as RonH reply here is a link for our own list of shortcuts to Sheldon's topics:

    http://www.bikeforums.net/showthread...-com-shortcuts

    This is in the Bicycle Mechanics section, the list and the subsequent replies are worth their weight in spokes and rims for me. I use it when I need to get information from Sheldon's treasure trove of bicycle knowledge. The member that compiled this list for BF did a great job that took a while and a lot of effort. 23 Kudos!!!

    Bill
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  6. #6
    I need speed AzTallRider's Avatar
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    Quote Originally Posted by lhbernhardt View Post
    Bolt Circle Diameter. If you scribed a circle around your cranks, with the center at the middle of the bb axle and the circumference passing thru the center of all the bolt holes of the chainring, the diameter of that circle would be the bcd.

    Standard road (and track) bcds:

    Shimano road: 130mm

    Campag road: 135mm

    Standard track (also Campag Nuovo Record road, back in the 70's): 144mm

    Old style Campag (going way back): 151mm (figure that one out!)

    Compact cranks: 110mm

    Luis
    And then there is the new Shimano "one size fits all" road crank with a 110mm BCD, 4 asymmetrical arms, and a hollow outer chainring. It goes up to 55/42, with a "compact" BCD. There is no 130mm version.
    "If you're riding less than 18 MPH up a 2% grade please tell people Coggan is coaching you."

  7. #7
    rebmeM roineS JanMM's Avatar
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    Lots of older Sugino, SR, etc. cranks were 110 and not Compact.
    RANS V3 - Ti, RANS V-Rex - cromo, RANS Screamer - cromo

  8. #8
    just keep riding BluesDawg's Avatar
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    110 was the old MTB size, later touring and lately, compact road.
    The more you ride your bike, the less your ass will hurt.

  9. #9
    rebmeM roineS JanMM's Avatar
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    Quote Originally Posted by BluesDawg View Post
    110 was the old MTB size, later touring and lately, compact road.
    Nit-picking: Sugino Super Maxy came on '79 Schwinn LeTour and Super LeTour bikes, before more than a very small number of factory-built MTBs existed.

    Question: Would a weight weenie go with a 110 crankset over a 130 with the same size rings? Smaller spider versus rings with more mass?
    RANS V3 - Ti, RANS V-Rex - cromo, RANS Screamer - cromo

  10. #10
    Senior Member NOS88's Avatar
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    Quote Originally Posted by JanMM View Post
    Nit-picking: Sugino Super Maxy came on '79 Schwinn LeTour and Super LeTour bikes, before more than a very small number of factory-built MTBs existed.

    Question: Would a weight weenie go with a 110 crankset over a 130 with the same size rings? Smaller spider versus rings with more mass?
    Didn't they also put them on some of the Voyaguers in the 70's too?
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    Favorite rides in the stable: Indy Fab CJ Ti - Colnago MXL - S-Works Roubaix - Habanero Team Issue - Jamis Eclipse carbon/831

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