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  1. #1
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    R4550 compact crank- question

    My LBS put on a Tiagra 4550 Compact crank50/34 on my Cervelo Soloist SL -- I had a Dura Ace crank 53/39 with a 12/27 cassette. The problem I first experienced with the 4550 was that I could not get into the 27 cog without the chain jumping off the big chain ring. After many trips to different bike shops it works now but I dont know exactly why nor hasnt anyone told me why .

    After looking through this forum I see that the 4550 is for a nine speed. It works now but what are your thoughts on this whole thing besides having a low level used crank on such a great bike.
    Would appreciate your thoughts -- the smaller crank seems to work well for me , thinking of going for a new Ultegra compact.

  2. #2
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    Sounds like the front derailler needs to be positioned better. I've had a similar problem using the smallest cog when in the middle ring of a triple crank. Fixed it by moving the front derailler a little closer to the chain, but not so close that it made any noise.

    The crank being 9 speed should have absolutely nothing to do with it. The only downside to using a 9 speed crank with a 10 speed chain would be slightly slower shifting. The only downside to using Tiagra in place of Dura Ace is some weight. How much do you care about a few ounces?

    According to weightweenies, Tiagra standard crank is 975 grams with BB and Ultegra SL Compact FC-6650-G is 811 grams with BB. 5.7 ounce difference.
    Last edited by joejack951; 05-19-09 at 08:09 PM.

  3. #3
    AEO
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    well, the 34T inner ring is the same thing for 9 and 10sp

    only the outer ring is different between the models.
    Food for thought: if you aren't dead by 2050, you and your entire family will be within a few years from starvation. Now that is a cruel gift to leave for your offspring. ;)
    http://sanfrancisco.ibtimes.com/arti...ger-photos.htm

  4. #4
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    You said the 9 speed crank should have no problem handling the 10 speed cassette.That is what my worry has been after reading that it was designed for 9 speed. i have been concerned that the nine speed thing was part of my problem,. Thanks-the weight thing is not a big factor. Seems to be working ok now.

  5. #5
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    Easy solution- don't use the 27 cog while on the big ring. That's cross-chaining, creating too large of an angle which increases friction, decreases efficiency, and shortens the life of the drivetrain.

    Al

  6. #6
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    You are absolutely right about the cross chaining. But I still would like to be able to get into the 27 with out the chain jumping.

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