Chain rub out of the saddle. What's flexing?
07-23-16, 03:57 PM
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Chain rub out of the saddle. What's flexing?
This question is more out of curiosity rather than having a problem to fix.
So I have a bike with a Claris triple at the front.
Sometimes when out to the saddle or pedaling hard I get chain rub on the FD. This is easily fix with the Claris's FD excellent trimming capabilities.
But I'm curious, what is flexing to cause this chain rub? The BB, The FD/seat-tub, the cranks something else?
The chain rub ONLY happens when I am pedaling down (i.e. at 4-6pm position) on the drive train (right) side.
Thanks!
So I have a bike with a Claris triple at the front.
Sometimes when out to the saddle or pedaling hard I get chain rub on the FD. This is easily fix with the Claris's FD excellent trimming capabilities.
But I'm curious, what is flexing to cause this chain rub? The BB, The FD/seat-tub, the cranks something else?
The chain rub ONLY happens when I am pedaling down (i.e. at 4-6pm position) on the drive train (right) side.
Thanks!
07-23-16, 05:20 PM
#4
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Aye, you can see for yourself: hold the saddle with one hand, the stem/bars with another, and put a foot on either pedal. Push, and you'll see the frame flexing. It's entirely normal, and nothing to be concerned about, unless it is accompanied by a creaking/ticking noise.
07-23-16, 05:22 PM
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In most cases it's mainly the seat tube (bottom bracket rocking side to side). It can sometimes also be the crank, especially if the chainring is attached to the crank arm instead of a fully independent spider.
Also, there's usually some deflection of the chainstays, which can cause chain rub at the back of the FD cage, vs. the front where seat tube deflection usually rubs.
Of course, it's never only one thing, so it's a bit of two or all three.
Also, there's usually some deflection of the chainstays, which can cause chain rub at the back of the FD cage, vs. the front where seat tube deflection usually rubs.
Of course, it's never only one thing, so it's a bit of two or all three.
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FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
Last edited by FBinNY; 07-23-16 at 05:28 PM.
