Compact Double Q
12-08-08, 04:24 PM
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Compact Double Q
Looking at the various Shimano groupsets available, a compact double doesn't appear to be one of the options. Can you DIY by replacing the chainrings with a 50 and a 34, or do you need to buy a dedicated crank assembly? And if so, does Shimano make one? And if you can DIY, will a 34 work with the stock 52?
12-08-08, 05:59 PM
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Looking at the various Shimano groupsets available, a compact double doesn't appear to be one of the options. Can you DIY by replacing the chainrings with a 50 and a 34, or do you need to buy a dedicated crank assembly? And if so, does Shimano make one? And if you can DIY, will a 34 work with the stock 52?
You need a new crank... "compact" cranks have 110mm BCD while "normal" Shimano cranks are 130mm.
A 38t ring is the smallest that will fit on 130mm BCD.
You could make a chainset with a 34t small and 52t large but it will shift poorly. 50/34 and 52/36 are about as far apart as you can go and still have decent shifting.
12-08-08, 06:15 PM
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Cool. If I get the regular double and decide to switch to the compact later (on the Ultegra group) are there any other modifications or changes needed?
12-08-08, 07:49 PM
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Shimanos compacts are outside the groups.
You need a new crank... "compact" cranks have 110mm BCD while "normal" Shimano cranks are 130mm.
A 38t ring is the smallest that will fit on 130mm BCD.
You could make a chainset with a 34t small and 52t large but it will shift poorly. 50/34 and 52/36 are about as far apart as you can go and still have decent shifting.
You need a new crank... "compact" cranks have 110mm BCD while "normal" Shimano cranks are 130mm.
A 38t ring is the smallest that will fit on 130mm BCD.
You could make a chainset with a 34t small and 52t large but it will shift poorly. 50/34 and 52/36 are about as far apart as you can go and still have decent shifting.
Shifting up front isn't that great, but you don't have to shift often. On a ride, the spread is far enough apart that I only shift the front if I know there are major climbs coming up. On all but the steepest terrain, the outer ring works. I might shift 2 or 4 times per ride.
