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Old 08-29-12, 12:07 PM   #1
VicM
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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!
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Old 08-29-12, 12:13 PM   #2
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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
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Old 08-29-12, 01:50 PM   #3
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Thank you, Luis!
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Old 08-29-12, 03:15 PM   #4
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Sheldon Brown has all the details with pics.
Here you go. http://sheldonbrown.com/gloss_bo-z.html#bcd
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Old 08-29-12, 03:35 PM   #5
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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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Old 08-29-12, 04:10 PM   #6
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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.
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Old 08-29-12, 04:52 PM   #7
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Lots of older Sugino, SR, etc. cranks were 110 and not Compact.
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Old 08-29-12, 09:08 PM   #8
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110 was the old MTB size, later touring and lately, compact road.
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Old 08-30-12, 04:13 PM   #9
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Quote:
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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?
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Old 08-30-12, 04:28 PM   #10
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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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