Quote Originally Posted by DebW
No, it is not normal for a cable to need retightening every 30-40 miles. What type of shift levers do you have? Integrated brake lever/shifters, downtube shifters, bar-ends? .... Maybe you've just crimped your current cable too much by having to readjust it so often, and now it pulls through the derailleur clamp. I'd try a new cable and if possible wait for it to finish stretching before retightening. I'd also be careful on shifts to the large chainring to not jamb the hard lever to the limit (if you have friction shifters).
Oops, sorry I didn't include it. I have integrated brake lever shifters. I sometimes think I'd be better off with old-fashioned shifters that don't "click" over into positions, though...

And you know, now that you mention it - the first few adjustments it looked like the part of the cable sticking out of the clamp was getting longer, but now I'm not sure after the last one. I'll bring that possibility up with the LBS if it needs to be adjusted quickly again...

Finally, I'm not being intentionally obtuse here, but: how do I wait for the cable to finish stretching before retightening? It seems to me that once it stretches to the point that I can't switch to the big chainring, it needs to be adjusted. Am I wrong?

Thanks for the ideas.