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Old 10-26-08, 06:21 PM   #1
Plow13
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replacing a chainring

i have a 46/36 crank up front (cross bike) and 12-25 in the back...Is it possible to remove the 36 ring and replace it with a 34? Or would i be better off going with a 12-27 in the back...
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Old 10-26-08, 06:57 PM   #2
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Quote:
Originally Posted by Plow13 View Post
i have a 46/36 crank up front (cross bike) and 12-25 in the back...Is it possible to remove the 36 ring and replace it with a 34? Or would i be better off going with a 12-27 in the back...
You need to answer this question yourself. We're not going to be riding the bike you are using.

http://www.sheldonbrown.com/gears/
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Old 10-26-08, 08:34 PM   #3
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Yes, it is possible to replace your 36t ring with a 34. They are available, will fit your crank, and will work fine with your existing front derailleur.
A Shimano short-cage rear derailleur can handle a maximum cog size of 27t, so you could install that too if you want.
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Old 10-26-08, 10:33 PM   #4
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i just wasnt sure if the 12 tooth jump would be too much....i may go with a 34 and 12-27
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Old 10-27-08, 12:44 AM   #5
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Operator is on the right path. Knowing the gear inches would help you know how much the differences in gears would affect you. What would be better would be a chart of them all. Google for one - they are pretty common and I have one as a background on my other computer.
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Old 10-27-08, 07:58 AM   #6
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If you really need a lower gear, do both. A 36x25 produces a 39 gear-inch low gear and a 34x27 gives you a 34 gear-inch low gear so the difference is significant 13%.

Shimano's 12x25 and 12x27 cassettes differ only in the largest two cogs so you give up nothing in the smaller, more used, cog spacing.
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Old 10-27-08, 08:06 AM   #7
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You may also want to replace the chain so you get equal wear.
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