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Derailleur hitting spokes, but not a bent hanger?

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Derailleur hitting spokes, but not a bent hanger?

Old 07-31-09, 10:38 AM
  #1  
RazorWind
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Derailleur hitting spokes, but not a bent hanger?

I've noticed that over the last two rides I've done on my '07 Cervelo Soloist Team, that the rear derailleur has started to touch the spokes when it's set to the shortest cog (the 25, in this case). I've had this happen in the past on a different bike, when the derailleur hanger got bent, which in two separate cases led to the wheel tearing the derailleur off the frame. It seems to have gotten progressively worse, as it started out doing this only when I'd be applying a lot of torque to the wheel, such as a steep climb in the shortest gear, but now does it almost constantly in that gear.

Here's the strange thing, though. As far as I can tell, the derailleur hanger on the bike in question is not bent at all. It doesn't appear to be, and it's easy enough to get the shifting adjusted. The shifting itself works fine. Furthermore, when I'm not actually riding the bike, even when it's on the inner-most cog, the derailleur has a couple of milimeters between it and the spokes. With this in mind, I'm thinking that the spokes may be too loose and are deflecting under load, and that I need to either have them tightened or go to a different wheel. The wheels in question are the Shimano R-500s that come with the bike, which apparently don't have the greatest reputation, but they've seemed at least serviceable.

Is the conclusion that this is a problem with the wheel and not the derailleur/hanger reasonable?

Last edited by RazorWind; 07-31-09 at 10:46 AM. Reason: I'm awesome like that.
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Old 07-31-09, 10:42 AM
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i'' save you the trouble, your limit screw is out of adjustment, read the park tools site and re-dial it in.
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Old 07-31-09, 10:50 AM
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Originally Posted by AngryScientist View Post
i'' save you the trouble, your limit screw is out of adjustment, read the park tools site and re-dial it in.
Hmm, maybe. I'll have to check that this evening.
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Old 07-31-09, 10:51 AM
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Most likely that, limit screw. Other possibility is a cracked frame. Not likely the wheel.
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Old 07-31-09, 10:53 AM
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Could also be loose spokes. And some wheels don't have much margin for error. Possibly a thin spacer on the freehub would help.
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Old 07-31-09, 11:01 AM
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1 vote for limit screw.
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Old 07-31-09, 11:07 AM
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Originally Posted by RazorWind View Post
As far as I can tell, the derailleur hanger on the bike in question is not bent at all.

Is the conclusion that this is a problem with the wheel and not the derailleur/hanger reasonable?
Sometimes one measurement is worth 1,000 guesses. "As far as I can tell" might not be good enough. I'd be for having your hanger checked with a gauge. Then you won't have to wonder if your conclusion is reasonable.
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Old 07-31-09, 11:08 AM
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Originally Posted by bikeybikebike View Post
1 vote for limit screw.
If it used to be OK I don't think so. Limit screws don't move unless somebody screws with them.
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Old 07-31-09, 11:57 AM
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Originally Posted by Retro Grouch View Post
Sometimes one measurement is worth 1,000 guesses. "As far as I can tell" might not be good enough. I'd be for having your hanger checked with a gauge. Then you won't have to wonder if your conclusion is reasonable.
if by gauge you mean straightedge, they yes, thats an easy one to check.
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Old 07-31-09, 12:17 PM
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Originally Posted by Retro Grouch View Post
Sometimes one measurement is worth 1,000 guesses. "As far as I can tell" might not be good enough. I'd be for having your hanger checked with a gauge. Then you won't have to wonder if your conclusion is reasonable.
My thoughts precisely. A derailleur hanger that doesn't look bent is often found to be not only bent but twisted when checked with the proper tool.
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Old 07-31-09, 12:23 PM
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under torque, the wheel's trailing edge of the spokes straighten out, and the leading edges go slack.

either the spokes are too loose, or you need to add a spacer at the end of your cassette.

or your RD hanger is bent.
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Old 07-31-09, 12:28 PM
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Yeah, if you're not shifting under load, just riding in the same gear under load, the derailleur doesn't see any tension from the chain, since all the tension is on the top of the chain from the cog to chainring. So it wouldn't make sense, if the problem appears only under load, that the derailleur is the problem. Scary though, wrapping a derailleur sucks. I've done it twice, on my mountain bikes.
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Old 07-31-09, 01:20 PM
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OR, you might experiment with a derailure with a longer cage. I experienced the problem you are having when I first put on the compact crank. The medium cage derailure solved the spoke dinging.
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Old 07-31-09, 01:24 PM
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Originally Posted by Fox Farm View Post
OR, you might experiment with a derailure with a longer cage. I experienced the problem you are having when I first put on the compact crank. The medium cage derailure solved the spoke dinging.
if the OP made no other changes, and his drivetrain used to work OK, skip this.

as mentioned the best place to start is making sure the hanger isnt bent then adjusting the limit screws. have the wheel spokes checked for tension to close the book on potential problems.
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Old 07-31-09, 03:38 PM
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If you think it's the wheel flexing, try leaning the bike to the left, does the rubbing sound increase? If you lean the bike to the right, does the sound go away?

As others said, it could be the inner-limit screw. This is easiest to test, so start with this. Tighten it up so that the RD can't even shift into the largest cog. Then slowly back it out 1/2 a turn until the RD shifts cleanly up to the largest cog and stays there.

Once the limit-screw is set optimally and you STILL get rubbing, take a picture directly from the rear and post it here. Some bent hangers are obvious. Others not-so-bent hangers require the special pivoting-tool that ensures the axis of the RD hanger-bolt is parallel to the rear-axle. Note that the hanger can be "straight", but still aimed inwards, causing the rotational-axis of the RD to not be parallel to rear-axle.

http://www.parktool.com/repair/readhowto.asp?id=39

Personally, I prefer the Shimano TL-RD11 tool over the Park Tool one. Fewer moving parts and more precise. Takes less time to use to make measurements as well.

Last edited by DannoXYZ; 07-31-09 at 03:42 PM.
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Old 07-31-09, 03:42 PM
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Your derailer hanger is bent, I promise you. Limit screws don't loosen themselves.

Take it to a shop with a Park Tools DAG (most shops) and they'll straighten it out.
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Old 07-31-09, 09:01 PM
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If you can see that your derailleur hanger is bent you are in some big trouble.
It is possibly bent/tweaked and the only way to know for sure is to put an adjustment/alignment tool on it and check.
If it is it is generally and easy tweak to put it back in alignment, then realign/adjust your rear derailleur.
A 5 minute alignment check is worth it.
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Old 07-31-09, 09:08 PM
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Originally Posted by AEO View Post
under torque, the wheel's trailing edge of the spokes straighten out, and the leading edges go slack.
And this is why I build wheels with the pull spokes heads out. The spoke crossings move away from the derailleur under torque. Well, that's what Sheldon says at least.

OP - have you increased the cable tension on the front der lately? Could be that the limit screw was off the whole time and you never had a high enough tension to move it into the spokes. Just another idea....
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