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Old 05-03-08, 06:24 PM   #1
sball32578
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Impact of changing inner chainring

So heres the deal:
I switched out my inner chaining (on a triple set). I went from a 28 to a 22. Now when i am in the smallest ring up front and the smallest cog in back my chain rubs the the outermost side of my front derailer.
I do not believe i shifted the derailer position while working on the chainring.
To fix this should i be looking at the length of my chain or derailer adjustments or what?
thanks
steve
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Old 05-03-08, 06:29 PM   #2
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Originally Posted by sball32578 View Post
So heres the deal:
I switched out my inner chaining (on a triple set). I went from a 28 to a 22. Now when i am in the smallest ring up front and the smallest cog in back my chain rubs the the outermost side of my front derailer.
I do not believe i shifted the derailer position while working on the chainring.
To fix this should i be looking at the length of my chain or derailer adjustments or what?
thanks
steve
Stop crosschaining and your problem is solved.

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On certain bikes, the chain may tend rub and rattle against the front rings while riding in certain gear combinations. This is common on many bike when riding in the so-called "cross-chaining" combination of the smallest front ring, and the smallest rear cog. An example of a gear combination that is likely to rub is shown below.
Quote from the Park Tool website
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Last edited by Wordbiker; 05-03-08 at 06:34 PM.
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Old 05-03-08, 07:48 PM   #3
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ditto
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Old 05-03-08, 07:51 PM   #4
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+1. There is absolutely no reason to ever use that gear combination.
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Old 05-03-08, 08:21 PM   #5
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It's also likely that the chain is rubbing the front derailruer "cage" because the derailruer is no longer close to the smaller ring as it was on the 28.

Last edited by kellyjdrummer; 05-03-08 at 09:29 PM.
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Old 05-03-08, 08:42 PM   #6
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+1. There is absolutely no reason to ever use that gear combination.
Why not, if it works without noise? I do it often, but I don't have a triple. The opposite "forbidden" combination (big-big) however, is usually quite noisy due to the high chain tension and I never use it, even accidentally, because I'm off the big ring long before I need those bigger rear cogs.
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Old 05-03-08, 08:50 PM   #7
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Because the angle is too great for the chain. It will cause greater wear and strain. You really want the chain to be as straight as possible. It would be better to find a different gear combo that gives you the same or close to that one that will give you a better chain line.
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Old 05-04-08, 08:22 AM   #8
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Why not, if it works without noise?
Because, if you calculate the gear chart, you will find there is at least one combination of middle chainring and larger cog that gives the same ratio and is easier on the chain.

Also, if the OP has exceeded the rd's capacity by going to the smaller granny ring, the chain will be completely slack in the small small combination if the chain is long enough to safely allow big-big as it must be.
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Old 05-04-08, 08:33 AM   #9
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Why not, if it works without noise?
Less Stress on the chain, therefore increasing lifespan
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Old 05-04-08, 09:25 AM   #10
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Stop crosschaining and your problem is solved.



Quote from the Park Tool website
Yup. Are you sure that it's the front derailleur the chain is rubbing on and not the big chainring? My compact double rubs on the big ring when I'm in the little/little combination. I use it as a audible indicator telling me to shift onto the bigger chainring.
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Old 05-04-08, 09:58 AM   #11
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I get the point about crosschaining, but even if i am going to avoid using the small small combo I would like for the chain not to rub in that combo. Before I switched rings (see original thread at top) it did not rub. I would like to be make it not rub again, even if I never use the combo.
In the meantime and in the future though I will not use the small-small. I dont think I really used it before anyway. But I still want it to work!
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Old 05-04-08, 10:11 AM   #12
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Then switch the chainring back.

You are obviously dealing with the effects of pushing the chain capacity of the derailleurs to the limits. When doing so, concessions must sometimes be made, one of which is giving up the crosschained gears.

I've done a fair amount of pushing the limits myself and have built drivetrains that exceed the limits to the point that certain gears couldn't physically be shifted into. I was a big boy about it and took full responsibility for what I'd done and took care not to use those combos. If you want to have a perfectly working drivetrain, run it within spec. Anything outside of that will be a "Class-B" fit and will come with some issues.
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Old 05-04-08, 10:13 AM   #13
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Originally Posted by sball32578 View Post
I get the point about crosschaining, but even if i am going to avoid using the small small combo I would like for the chain not to rub in that combo. Before I switched rings (see original thread at top) it did not rub. I would like to be make it not rub again, even if I never use the combo.
In the meantime and in the future though I will not use the small-small. I dont think I really used it before anyway. But I still want it to work!
The new chain angle created by your smaller chain ring is causing this. It's a simple drivetrain geometry issue. You don't have much choice there if you want to keep the 22 ring.
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Old 05-04-08, 10:28 AM   #14
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Originally Posted by OLDYELLR View Post
The opposite "forbidden" combination (big-big) however, is usually quite noisy due to the high chain tension and I never use it, even accidentally, because I'm off the big ring long before I need those bigger rear cogs.
It's true that big-big is far noisier than small-small on most drivetrains. However, assuming you pedal at the same cadence and power, chain tension is smaller in the big ring and greater in the small ring. So the reason for the noise is something else.
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Old 05-04-08, 11:13 AM   #15
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Just to set the record straight, I don't deliberately always use the small/small combination as a matter of course. However, when descending a mild hill, I might inadvertently go to it and not even realize because it's so smooth. So I leave it there temporarily rather than double shifting to a more "correct" combination. If it sounds and feels smooth, it can't be doing much damage for a few seconds. The thing about riding bikes is that if it doesn't feel "right", you're probably doing something wrong. That's whey so many people give up when they find it too hard.
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Old 05-04-08, 11:26 AM   #16
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The new chain angle created by your smaller chain ring is causing this. It's a simple drivetrain geometry issue. You don't have much choice there if you want to keep the 22 ring.
Yup. I understand the OP's concern. I feel that way too. The reality, however, is that roadfix and Wordbiker are right. That's probably why the bike didn't come with a 22 ring in the first place. If you want the 22 ring you're going to have to put up with the class B fit.
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Old 05-04-08, 08:42 PM   #17
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even if i am going to avoid using the small small combo I would like for the chain not to rub in that combo. I would like to be make it not rub again, even if I never use the combo.
Easy fix: Never use that combo and pretend that it doesn't rub in that combo.
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Old 05-05-08, 01:29 AM   #18
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Put your bike on a stand and shift to the smallest ring in front then start on the largest rear cog and change down until you see where the rubbing starts then file it away and don't use anything but the good combinations.
I have a campy triple and changed my 30 down to a 28 on my road bike and 26 on my cross bike. I just never use anything but the 5 largest cogs with the inner ring. I never shift out of my middle chain ring unless I really need the lowest gears...90% of the time I ride my triple as a double.
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