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Old 04-07-10, 09:36 PM   #1
5kdad
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Double chain ring vs. compact

What's the difference between a double chain ring and a compact chain ring?
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Old 04-07-10, 09:38 PM   #2
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BBC on a Std road cranks double is 130mm compact is 110mm.
This is distance from bolt to bolt center to center.
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Old 04-07-10, 09:59 PM   #3
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The BCD Bolt Circle Diameter for most modern cranksets, including Shimano are 130 mm. Compact cranksets have a 110 mm BCD and can accept smaller chainrings. Campagnolo standard cranksets have a 135 BCD.
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Old 04-07-10, 10:10 PM   #4
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The BCD Bolt Circle Diameter for most modern cranksets, including Shimano are 130 mm. Compact cranksets have a 110 mm BCD and can accept smaller chainrings. Campagnolo standard cranksets have a 135 BCD.
Of course to complicate things the TA cranks on my bikes have a BCD (50.4 mm) that's less than half the size of the current 'compacts' but they're considered regular size.

And to JTGraphics:
No, the BCD is the diameter of a circle that would pass through the center of the bolts. The center-center distance between bolts is 76.4mm for a 130mm BCD and 64.7mm for a 110mm BCD.
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Old 04-07-10, 10:24 PM   #5
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On the off chance you meant compact crankset instead of an individual chainring, the idea is to give you a lower/wider gear range without going to a triple. The size difference between the rings will be greater and the size of the rings themselves will be smaller than on a more standard double.
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Old 04-08-10, 01:40 AM   #6
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How about this, a compact crank usually has two chainrings,in the 48 and 34 range, while a standard usually has them in the 52 and 42 range. Give or take a tooth or two...
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Old 04-08-10, 08:30 AM   #7
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A "standard" road bike double is typically a 53/39. A "compact" road bike double is typically 50/34.
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Old 04-08-10, 08:52 AM   #8
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A compact crankset is a double crankset. Not all double cranksets are compact cranksets. The cyclocross crank (46/38) on my hybrid is neither a compact not a standard road double.
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Old 04-08-10, 08:54 AM   #9
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Originally Posted by prathmann View Post
Of course to complicate things the TA cranks on my bikes have a BCD (50.4 mm) that's less than half the size of the current 'compacts' but they're considered regular size.
And they make great "compact" cranks (43/30 in this case):
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Old 04-08-10, 04:54 PM   #10
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And they make great "compact" cranks (43/30 in this case):
Lyotard pedals!!!!
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