My chain is rubbing against my big chainring when on the small chainring

Discussion in 'Cycling Equipment' started by xxtimber, May 3, 2010.

  1. xxtimber

    xxtimber New Member

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    Hi

    I have an Ultegra front derailleur, Truvativ Elita crankset w/ powerglide chainrings, Sram 951 9 speed chain, and 9 speed Tiagra cassette.

    When on the small chainring, in the smallest 3-4 cogs, the chain rubs against the big chainring. I have never encountered this on a bike before. I have adjusted the front derailleur already. What is wrong??
     
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  2. xxtimber

    xxtimber New Member

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    I had the same problem previously with an octalink bottom bracket and dura ace 9 crankset so I repaced the crankset with the Truvativ with GXP external bottom bracket but same problem...
     
  3. Peter@vecchios

    [email protected] New Member

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    What you are seeing is normal for multi cog systems with modern chainrings with all sorts of pins and ramps on the big ring to aid in shifting under load plus with smaller small chainrings...normal.
     
  4. alfeng

    alfeng Well-Known Member

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    How long/short are the chainstays on your bike?

    Is the rear spacing on your bike 130mm or 135mm or __(?)__?

    Regardless, on one of my bikes whose rear spacing is 130mm & the chainstay length I measure as a relatively short 40.3mm, when the chain is on the small chainring it does NOT rub against the large chainring regardless of the cog that the chain is on ... I do have to trim the front derailleur (6500) when the chain is on the smaller cogs if series of shifts begins with the chain on the larger cogs ...
    The particular bike has a 9-speed Shimano chain (CN-HG92) + a 7700 crankset (53/39, 109.5mm BB) & a Hugi 240 rear hub & 9-speed Shimano cassette.
    While some people believe that the chain width doesn't matter, FWIW, I recommend you consider switching to a 9-speed SHIMANO chain ... it may-or-may-not resolve your problem.
     
  5. dhk2

    dhk2 Active Member

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    alfeng, is the Shimano 9 sp chain narrower than a SRAM chain? I use HG-93 chain currently; have used SRAM in the past but never measured either. The KMC chain on my track bike is definately wider....that I can tell :)

    BTW, I do get a light rubbing from the big ring when on the smallest two cogs. It's not severe, and since I don't cross-chain not a problem at all. My bike has an FSA triple chainring with the "medium" ISIS spindle...113mm.
     
  6. alfeng

    alfeng Well-Known Member

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    I don't know -- I don't have digital calipers; but, I am going to guess that the Shimano chain MUST BE narrower than the particular SRAM chain which the OP is currently using.

    Cambria used to list the different widths of all the chains they sold ... but, I don't think they do any longer (at least, I couldn't find the information the last time I looked a year-or-so ago) ... if I had known that the information would disappear then I would have copied all of it down for future reference ...

    The only 9-speed SRAM chains that I have are the 89R which I actually bought to use with my Campy cassettes ... but, I subsequently opted to focus on using the 9-speed Shimano cassettes & Shimano chains (why pay more?) ...

    One of these days I guess I'll put one of those 89R chains on to see whether there is rubbing when the chain is on the inner chainring & the smaller cogs ... if it rubs, then I'll relegate the 89R chains to the non-Shimano cassettes.

    Is that on a frame with a 135mm rear or a 130mm rear?

    On a frame with a 130mm rear, I would think that the 113mm spindle should be more than long enough to preclude the chain rubbing against the outer chainring when the chain is on the middle chainring & the smaller cogs ...

    If the frame has a 135mm rear, then changing to a 118mm spindle should eliminate the chain rub (if it ever becomes something that you want to achieve).
     
  7. curby

    curby New Member

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    OP,

    Last 3-4 cogs is unreasonable, last 2 Okay but there should be something you can do.

    What bottom bracket you are using? Rear wheel/hub?

    The chainline should be checked on the bike as well as the chainring distance from the bike's centerline, Shimano is 43.5mm from the middle of the crank to the middle of the seat tube for a double if I remember correctly, Truvativ is probably similar but it is something to check. The chainline is an imaginary line that runs from the middle of the chainrings parallel to the bike centerline back thru the cogset, that line should ideally run right thru the 5th cog of a 9sp cassette. Bottom bracket spindle and frame alignment are the most likely factors to produce bad chainline. In your case we would expect the cranks to be too far inboard which allows the chain to rub the large chainring in the gear combinations you describe.

    Also sometimes a spacer behind the cassette isnt really necessary but the hub manufacturer says it is to run 9sp so ppl put it on. I find that my Dura ace cassettes have to have a spacer and my SRAM cassettes dont need it. The Dura ace cogs end up further outboard and my 2nd smallest cog brings the chain out far enough to catch on the ramps/pins on the backside of the large chainring.

    good luck

    curby
     
  8. dhk2

    dhk2 Active Member

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    alfeng, your guess appears correct. I put the calipers on the HG-93 chain on my bike, then a Wippermann, finally a SRAM PC-58. Measuring across pins (max width), was surprised to find the Shimano @ 6.5 mm, the Wippermann @ 6.8, and the SRAM a "whopping" 7.1mm.

    Honestly didn't expect to find significant differences like this, but I'd never actually measured chains before. Agree with your suggestion to the OP that a Shimano chain may help reduce the problem.

    Oh, my bike has a 130 mm rear axle. Now that I think about it, the chainring interference was noisier with the SRAM chains I used when the bike was new. With Shimano chain, the noise is slight, and since I rarely use the smallest two cogs, not a problem for me. The 113 spindle "looks right", with the middle chainring aligned with the middle cog, and provides good shifting on the inner ring with the four larger cogs. Sadly, those I do use a lot :)
     
  9. xxtimber

    xxtimber New Member

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    Thanks guys, I really appreciate the help. I've always heard that SRAM chains were 100% cross compatible with Shimano but that could be the problem. And I will check the chainline. :D
     
  10. alfeng

    alfeng Well-Known Member

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    Thanks for taking the time to measure the widths of the chains you had on hand ...

    FWIW. I eyeballed one of the SRAM PC89R chains that I have, and it is ~6.9mm +/- wide ... another FATTIE.
     
  11. dhk2

    dhk2 Active Member

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    Well, probably should be mentioned that my measurements were just done on one sample of each chain. Have no idea how production variance would affect the width, but seems to me it would likely be held to 0.1mm or less. The Wipper and SRAM chains I had lying around were several years old. Would be interesting to see the drawings on these to look at the actual spec value and tolerances for width, or if the spec width has changed at all over the years. .
     
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