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Turns out my front chain rings are biopace, after I thought they had disappeared!

I've got a problem with the chain rubbing the front deraileur at a certain point every rotation. I only get this in the highest gear on the inner ring and it happens from about the 4th gear when on the outer ring. getting gradually worse when changing up to the highest gear.

Not sure if it's a trim or height problem or both :S

when in the small inner ring height should not be a problem.

Front deraileur

But it could be height issue when on the highest gears on the outer ring.

Setup

  • Dura ace deraileur front and back
  • 105 cranks and chain ring
  • unknown back sprocket set
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If it's only rubbing once a revolution then the ring or crank is bent. If it's rubbing twice a revolution you need to adjust your derailer. Generally the largest ring is not Biopace. –  Daniel R Hicks May 2 '12 at 10:17
    
opinion –  will May 2 '12 at 10:25
    
Can't make out much on the video. (And I see that your large ring IS Biopace.) –  Daniel R Hicks May 2 '12 at 11:24
    
@will: Single word comments and answers are discouraged. Please explain the contents of the link. We are trying now to get video embedding enabled on the site. Using video in that fashion is the precise argument they are using to prevent it. Please don't do this. –  zenbike May 2 '12 at 11:47
    
Apologies zenbike I added the video as another another view of the problem. @Daniel R Hicks Yup quality pretty shite. I can't really see much of the chain ring being bent. How can I test and if needs be fix? –  will May 2 '12 at 16:11
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1 Answer 1

Keep in mind that there are 5 adjustments on a front derailer:

  1. Low limit
  2. High limit
  3. Cable adjustment -- selects where the derailer stops for intermediate cogs
  4. Height above crank
  5. Angle on seat tube

For subtle chain rub problems sometimes adjusting the angle (very slightly!) is the best approach.

But remember that if the rub is only once a revolution it suggests that the ring, arm, or crank is bent.

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