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# Compact Cranks & Chain Shortening

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# Compact Cranks & Chain Shortening

04-16-07, 08:25 AM
#1
bluehorizons
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Compact Cranks & Chain Shortening

So I just put a compact crank on my road bike, and wondering how much i should shorten the chain by. Is there some sort of ballpark that folks have used when only changing from a 52/39 to a 50/34? I know I can test for the correct chain length, but just curious if everyone settles in on a similar number of links to drop.

04-16-07, 08:26 AM
#2
bdcheung
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Chain sizing 101:

1. Wrap chain around biggest chainring and biggest cog (don't thread through rear derailleur).
2. Add two links (an inner and an outer) to the spot where the chain overlaps.
3. That is your chain size.

I think I removed like 3 whole links when I went from standard to compact, but don't quote me on that.

If you're math inclined, you can work out your chain length using this formula:

L = 2 (C) + F/4 + R/4 + 1

where
L = Chain length in inches. Round the final result to closest whole inch figure.
C = Chain stay length in inches, measure to closest 1/8.
F= Number of teeth on largest front chainring.
R= Number of teeth on largest rear cog.
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04-16-07, 08:30 AM
#3
botto
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i didn't shorten my chain when i made a temporary 2 week long switch.
04-16-07, 08:50 AM
#4
Patriot
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I just put the chain on the small-small gears, then adjust the length so that the rear der is at a pretty good angle to the rear, but still enough tension on the chain. That way, when I put it back up to big-big, the rear der is angled about the same forward. After the angle is about the same forward as reverse for the opposite ends of the spectrum in gears, I then remove the necessary links.

Seems to work easy enough for me, and I've never had a chain skip or problems with shifting.

Also, a as suggestion, if you have thousands of miles on the chain to begin with, you may want to simply replace the chain when changing out any other parts of the drivetrain. It helps save on excessive wear.
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04-16-07, 10:01 AM
#5
urbanknight
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You only need to shorten the chain if the small/small combination sags or makes the rd rub the cogs.
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04-16-07, 01:24 PM
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Surferbruce
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i think i only removed one full link (inner and outer) and was spot on.
04-16-07, 01:51 PM
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OP - I switched from a standard triple to a compact double (FSA); based on suggestions I saw here on this forum, I replaced the long-cage rear derailleur (Shimano Ultegra) with a standard cage rear derailleur. As a net result, I didn't have to resize the chain at all.

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