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  1. #1
    Junior Member
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    Feb 2009
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    Replace Cogs / Crankset

    I rode my bike across the country last summer so I badly need to replace my cogs / cassette. I have a Giant Defy 1 with

    cranks FSA Gossamer MegaExo, 30/39/50
    cassette Shimano 105 12/27, 10-speed

    Are there any other parts I might want to replace (aside from the chain)? Do the teeth on the derailleur wear out at about the same time? Probably a stupid question, but I'm new to actually doing any work on my bike, lol

  2. #2
    Senior Member
    Join Date
    Apr 2009
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    New Rochelle, NY
    My Bikes
    too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
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    I assume you've measured the chain for stretch, or the cassette is rough, otherwise you might be replacing parts that still have decent life in them. Unles you're sure the cassette and chainrings are toast, take it one step at a time.

    Measure the chain and decide if it's time to replace it (1/2-3/4% stretch or 1/16"+/12"). If so, replace the chain only and see how it runs. If it runs OK you can put off replacing the cassette and chainring. Otherwise try replacing the cassette but hold off on the chainrings which generally last much longer. With good care you should replace 3 or more chains before replacing the cassette.

    Lastly if the chainrings are shot, decide if it's only one or all three, in which case you have an economic decision because often 3 chainrings cost more than an entire crankset.

    As for the RD pulleys, most last a long time because they don't run under much load. (the ones on my old road bike are over 50,000 miles old and still fine). Examine them by eye and listen or feel for vibration as the chain runs on them, if you don't see, hear, feel a problem you don't have one.
    FB
    Chain-L site

    An ounce of diagnosis is worth a pound of cure.

    “Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

  3. #3
    Mechanic/Tourist
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    Apr 2007
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    Syracuse, NY
    My Bikes
    2008 Novara Randonee - love it. Would have more bikes if I had time to ride them all. Previous bikes: 1968 Motobecane Mirage, 1972 Moto Grand Jubilee (my fav), Jackson Rake 16, 1983 C'dale ST500.
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    Just replace the chain if the cogs are bad. Are there any other parts to replace after a cross country ride? Possibly. We can't inspect it here so take it to a shop for an evaluation of bearings etc.

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