So my new Trek has been having some front shifting problems, getting progressively worse. Dropping the chain both high and low, rubbing all over. This morning I gave in and took a look at it. I wrench on robots all day at work, I don't spend as much time on my bikes as I used to.
Lo, the derailleur had rotated and dropped about 2mm! Did a nice number on the paint, too. Investigating, the clamp bolt was barely doing anything. Not even what you'd call "snug".
Sure, I understand with lightweight frames you don't want to overtorque anything, having the risk of cracking the carbon or crumpling the metal and destroying the frame. But you don't want to undertorque it excessively, either. There is such a thing as PROPER torque. As my brother the engineer explained, proper torque for a fastener can be calculated. You want to stretch the threads just a wee bit, so they "lock" together. An experienced mechanic can feel this, to an extent. Where proper torque is important, good thread prep and a torque wrench are your friends. In seriously important fasteners, you can even buy special fasteners that limit their own torque, no torque wrench required!
Granted, the extremely thick paint on the Trek (I suspect they did not bother to remove the botched original paint, just sanded it down a bit and shot another coat over it) complicates matters.
But seriously. Torque. It's your friend. Too little is generally better than too much, but best of all is "just right".
The derailleur is to my liking now; lined up, vertical position good, stops set correctly, cable tension good. With proper setup, even the narrow SRAM front derailleur requires minimal trimming. I can see why bike shops may not like SRAM, because they do require more setup time than the competition's components.
I'm looking forward to today's ride and enjoying correct derailleur function!
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