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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 10-20-09, 05:56 PM   #1
jtuba
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going from 50/34 to 53/39 crank

Other than moving the front derailleur, do I need to lengthen the chain or anything else?
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Old 10-20-09, 06:00 PM   #2
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Very possibly the chain... Check the big/big combination and note whether the rear derailleur pulley has enough clearance.
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Old 10-20-09, 06:02 PM   #3
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I just did this in reverse swapping an Ultegra 53/39 for a 50/34. Adjusted the FD and took a couple of links out of the chain.

More than likely you'll have to add a couple.
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Old 10-20-09, 06:07 PM   #4
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Possibly need to lengthen the chain. If the chain was previously sized to be as short as possible with the 50T ring, then it will be too short for 53T. See here: http://sheldonbrown.com/derailer-adjustment.html#chain

Before adding links, think about this:
1) Does the chain require a special connecting pin (Shimano) or quick-link? The design of newer chains allows the chains to be stronger, but removing and re-connecting the same pin can damage the outer plate, creating a significant weak spot.

2) How old is the chain? If it's stretched enough, it may be best to just replace the whole chain.
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Old 10-20-09, 06:09 PM   #5
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Also, going to a new crank may require a new bottom bracket if the crank/bottom bracket interface is different (square-taper vs. ISIS vs. External, etc.) or a different spindle length is required.
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Old 10-20-09, 07:31 PM   #6
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Don't bother changing the botom bracket or even the crank arms.
Chances are your 50/34 is a 110 not a 130mm.
I made the same move as you.
I just ordered a 52/38 set of chain rings.
The theory is that the change only cost about $150 and if I am planning on a big hard hilly Century the chain rings can go back to 50/34 in a couple of minutes.

My problem with the 50/34 was that I didn't like the big gear spread. If you are just looking for speed it is not rally going to gain you very much. Why not install a 23-11 or a 25-11 cog? or If you really believe that you have power to burn try a 21-11 cog.

Much easier to change sprockets than chain rings.
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Old 10-20-09, 07:36 PM   #7
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Quote:
Originally Posted by jtuba View Post
Other than moving the front derailleur, do I need to lengthen the chain or anything else?
You have to check the chain length in the big/big combo.
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Old 10-20-09, 07:41 PM   #8
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If the problem is the big ratio jump between the 50 and 34 another option would be replacing the 34 with a 36.

Al
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Old 10-21-09, 12:25 PM   #9
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Thanks for all of the input. I'm in the process of acquiring parts so I can build up a second bike. I would put the 53/39 on my main bike and put the compact on a second bike. Some good CL deals on cranks now. I'll get some advice from the LBS as far as chains go too.
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Old 10-21-09, 01:11 PM   #10
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Measure the chain with a good steel ruler.
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