Bicycle Mechanics - I know I'm not THAT strong... right?

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jbarros
09-04-07, 10:48 AM
So,

I got a new steelie a while back (Jamis Aurora) and it's coming up on time to adjust my derailers etc (which is a little intimidating, as I've only done it with downtube friction shifters before, and this is a STI brifter system) but with them just a hair out of alignment, I noticed on downstrokes I hear a grinding, and looking down, it appears that the chain is rubbing the front derailer when I do....

Am I flexing the frame to cause this?

I'm a rather weak commuter (< 15 miles roundtrip a day) and this isn't a 15 lb light is more important than anything flexy flier, although it IS a price-point bike)

Or is it something else?

Thanks.

-- James

Mr Pantani
09-04-07, 01:37 PM
It happens.
tellyho
09-04-07, 01:58 PM
I don't think it's frame flex. More probable is an out-of-round chainring (most are, by the way) and/or a misadjusted FD. You're not in a bad combo when this happens, are you (small/small, big/big). Cross chaining is a no-no.

jbarros
09-04-07, 02:46 PM
I don't think it's frame flex. More probable is an out-of-round chainring (most are, by the way) and/or a misadjusted FD. You're not in a bad combo when this happens, are you (small/small, big/big). Cross chaining is a no-no.

Big (front) small (back) and generally closer to mashing than spinning when it happens.

-- James
Crestwooddan
09-04-07, 04:26 PM
You may be flexing the chainring/crank while mashing in the big front/small back combo. On my old friction shifter steely I have to nudge the front D when the back D travels to an opposite side. I bet there is an appriciable angle on the chain in the big front/small back combo.



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