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  1. #1
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    Chainring replacement

    I have a 4.7 Madone with an Ultegra compact setup that is a few years old. When cleaning it up today, I noticed the teeth on the outer ring are fairly jagged with uneven wear. Some are downright pointy. Now I haven't felt much slip or had any gear change issues, but I'd like to prepare for a replacement and have a few questions I'm hoping you can help with.

    When do you know it's time?

    Should you replace both? I'm in Flat Florida so I don't use the other ring very often.

    Should I stick with Shimano or is there better option for someone that does it for exercise and is a big guy?

    Is this something I can do myself? It looks like it's attached with 5 Allen bolts. Do you just unbolt, remove, bolt new one on?

    Thanks for the help!

  2. #2
    Senior Member escarpment's Avatar
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    If your going to do one, do both. If the inner one is rarely used I might not worry about it. It doesnt sound like it needs to be asap, but it cannot hurt. You could do it yourself without taking the crank off, but It might be difficult to get the force needed to loosen/tighten the bolts. It will be much easier if you take it off.

  3. #3
    just another gosling Carbonfiberboy's Avatar
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    The question that jumps into my mind is - how many chains have you gone through so far on that bike? If the teeth are that bad and your chain isn't slipping, is it possible that you have the original chain on there? In which case, yes, two new rings and a new chain. Probably new chain anyway.

  4. #4
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    On modern cranks the teeth are uneven to help shifting. Wear on a crank should be pretty even and should make the teeth look like shark's fins. What you're describing sounds like the shifting aids that exist on modern cranks.

  5. #5
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    Quote Originally Posted by ivan_yulaev View Post
    On modern cranks the teeth are uneven to help shifting. Wear on a crank should be pretty even and should make the teeth look like shark's fins. What you're describing sounds like the shifting aids that exist on modern cranks.
    Possible, need a picture to really tell.

    If they really are worn, I'd go for a 53/39 chainring combo. On the flats, that should be quite nice

  6. #6
    Senior Member echotraveler's Avatar
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    Id change both rings, the chain, and probably the cassette.

    As you ride with a worn chain your rings and cassette change their correct forms.

  7. #7
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    If changing the chain rings is in order, you can certainly do it yourself. I have never needed to remove the crank to do it. It just requires a little wiggling of the rings after you detach them to get them over the arms. What you do need is two tools, one to keep the rear or inside bolt half (or nut?) from turning while you unscrew the front or outside bolt. Check and see which type tools are required for the front and back. Don't forget to specify your "bolt circle" measurement to get the right rings that fit your bike. On an Ultegra compact the correct measurement is 110 mm.
    Last edited by rpenmanparker; 04-16-13 at 05:47 AM.

  8. #8
    Senior Member RollCNY's Avatar
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    Isn't an Ultegra compact crank always a 110 BCD?

  9. #9
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    Quote Originally Posted by RollCNY View Post
    Isn't an Ultegra compact crank always a 110 BCD?
    Yes. I was already in the process of correcting my post. Thanks for the catch.

  10. #10
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    To check wear one thing I do is put the chain on the big ring. Pull the chain off the big ring at the 3 o'clock position. You'll see some movement around the whole chainring but if you see substantial movement at the top and bottom it means the chain isn't engaging the teeth properly.

    This is more an exercise in checking overall wear. It's not an exercise in determining what needs replacing (it could be the chain or the chainring or both). The good thing is that it's free, it takes a second, and you're on your way.

    If you have a new/less-used bike then do the same thing on that for comparative purposes. The chain will feel much more snug.

    Although you may not need to replace your inner ring you may want to if you size up on the big ring. If you go from a 50 to 52T outer ring and you keep your 34T inner ring you'll be shifting across an 18T difference and your rear derailleur will need to take up an extra 2T of slack. If you get a 52/36 combo then you'll stay at a 16T difference and your rear derailleur will act the same (you need a longer chain though).

    Finally you may go a bit bonkers with the inner ring, pending frame clearance. On flat roads you don't need a 39x27 or whatever. You may take a page out of the Paris Roubaix book and use a larger inner ring. 52x46 or something odd like that (I chose 46 because you can get single chainring purpose 46T rings). This way you'll have more usable gears in smaller increments and you'll spread wear across more "gears" (two chainrings instead of one and you'll use more of your cogs than if you only used your big ring).

  11. #11
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    Quote Originally Posted by Carbonfiberboy View Post
    The question that jumps into my mind is - how many chains have you gone through so far on that bike? If the teeth are that bad and your chain isn't slipping, is it possible that you have the original chain on there? In which case, yes, two new rings and a new chain. Probably new chain anyway.
    Yes, they are original rings and chain. Different cassette.

  12. #12
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    Excellent insight everyone. Thank you. I did not know the rings had teeth of different angles/shapes. I'll snap some pics today. As mentioned, I haven't had any side effects (knock on wood), so maybe it's not that worn.

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