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Chain rubbing issue
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I have a fairly new Cannondale Ironman 2000 (stock) and am having some shifting issues. I know just enough about bikes to be dangerous but not enough to actually fix much (yet). My problem is when I am on the small chainring up front and either of the smallest two rings on the back, my chain rubs against the large chain ring in the front as it comes off the cogsof the small one. It makes that annoying noise as well as not feeling smooth. Is this something that is easy to fix as my LBS is 30 minutes away? Any help would be appreciated.
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Re: Chain rubbing issue [MultiSport PDX] [ In reply to ]
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Patient: It hurts when I touch this spot

Doctor: Well, don't touch it.

The "problem" you're having is quite normal, especially in recent years as 53/39 chainrings are the norm (14t difference), rather than in the old days with a 52/42 setup (10t) difference. I wasn't riding in the days of the 52/48 and such :-).

You should not be using those gears, as the chain is at an excessive angle, especially so if you have 650c wheels and a correspondingly short chainstay. If you need to use the 39/13 or 12 (assuming a 12t smallest cog), these are almost the same as a 53/17 or 16, which will give you a much better chainline.

Hope that helps,

J.
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Re: Chain rubbing issue [jasonk] [ In reply to ]
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I am indeed on 650c's. I guess I was a little naive to think that I could actually use all those fancy gears back there. The thought had not crossed my mind that it was an actual bike limitation. I guess that is what happens when a runner buys a road bike after being on fat-tires for the last several years. Thanks for the info.
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Re: Chain rubbing issue [MultiSport PDX] [ In reply to ]
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Multisport, I'd suggest that you look up (you can find charts all over the web, I think www.analyticcycling.com has one) the gear lengths of all your possible combinations. Without knowing what cassette you have, I'd still venture a guess that you'll find a couple of 53 x something gears that are REALLY close to the 39 x somethings you aren't able to use. Bike manufacturers do a fairly good job of spec'ing appropriate gearing with availability of reasonable steps but taking unusable combinations into account. Its a tedious thing, but knowing your available gear lengths will help you make wise choices on the road. At this point I could trail off on a long digression about gear selection/tactics/history....but I won't....

1st Place, 50-55 2018 USAT Duathlon Sprint Duathlon National Championships, National Champion; 2nd Place Overall, 2018 Virginia Duathlon; 3rd Place, 50-54, 9th overall, USAT Long Course Duathlon (Miamiman); 4th Place Masters, 10th overall, 2018 Kiawah Island 1/2 Marathon
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Re: Chain rubbing issue [TriBriGuy] [ In reply to ]
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Thanks for the info... does the following look right concerning my 39/53 - 12/23 gearing setup? The bold area indicating the unusable gears... 650c's....

12 13 14 15 16 17 19 21 23

39 83.2 76.8 71.3 66.5 62.4 58.7 52.5 47.5 43.4

53 113 104.3 96.9 90.4 84.8 79.8 71.4 64.6 59
Last edited by: MultiSport PDX: Mar 25, 03 10:59
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Re: Chain rubbing issue [MultiSport PDX] [ In reply to ]
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Without checking that looks about right. Notice that 39 x 12 roughly = 53 x 16, 39 x 14 roughly = 53 x 19, etc. etc. I wonder about your claim to have FOUR unusable gears, though. Usually recommendations are that you shouldn't use 39 x 12,13 OR 53 x 21,23. You should be able to use your 39 x 14,15 though, especially on a Cannondale since its chainstay lengths are relatively long for 650 (as opposed to bikes like the P2k/P3 from Cervelo).

1st Place, 50-55 2018 USAT Duathlon Sprint Duathlon National Championships, National Champion; 2nd Place Overall, 2018 Virginia Duathlon; 3rd Place, 50-54, 9th overall, USAT Long Course Duathlon (Miamiman); 4th Place Masters, 10th overall, 2018 Kiawah Island 1/2 Marathon
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