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Old 10-18-10, 12:04 AM   #1
bikonator
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Distance between the center of the bottom bracket to the big chain rings center?

Does anyone know the distance between the center of the bottom bracket to the big chain rings center? (in mm)
Thank you
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Old 10-18-10, 12:37 AM   #2
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Are you talking about chain line distance? (center of BB to center of chain ring--normally middle ring for triple, between big and small for double) If so, it would depend on what crank set and BB you use, as there are many different length spindles for different cranks, as well as different types of BB--square taper, ISIS, Octalink (a couple diff. I think), and the newer external bearing BB's. Depending on the setup you have, it could make quite a difference in the distance.
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Old 10-18-10, 06:44 AM   #3
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For a standard double crank, the chainline is 43.5mm, but that's from the center of the frame to an unmeasureable point, centered between the chainrings. The tip of a tooth on the big ring should measure 47-48mm, since the tooth to tooth spacing is in the 7-8mm range.

Triple cranks are measured to a more sensible point - the tip of tooth on the middle ring, but the chainline varies from 45-47.5mm, depending on the brand and seat tube diameter.
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Old 10-18-10, 07:39 AM   #4
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Originally Posted by DaveSSS View Post
For a standard double crank, the chainline is 43.5mm, but that's from the center of the frame to an unmeasureable point, centered between the chainrings. The tip of a tooth on the big ring should measure 47-48mm, since the tooth to tooth spacing is in the 7-8mm range.
Yeah, the chainline datum point is in thin air for a double but it can be determined reasonably accurately by recording the distance from the frame's center line to each of the chainings and calculating the midpoint.
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Old 06-25-11, 09:48 AM   #5
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Thank you everyone for your help.
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Old 06-25-11, 10:24 AM   #6
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http://www.sheldonbrown.com/chainline.html
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Old 06-25-11, 10:40 AM   #7
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Originally Posted by bikonator View Post
Does anyone know the distance between the center of the bottom bracket to the big chain rings center? (in mm)
Thank you
It's easier to measure from the centerline of the seat tube.

Brad
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