gears slipping
I have a Cannondale touring bike with a Shimano XT rear derailleur that slips. When I'm going up a steep hill and I think I have shifted into the lowest possible gear, I find that perhaps after 6 or 8 pedal revolutions, the chain THEN moves on to the largest cog on the sprocket cluster (in other words, the lowest gear where I already thought I was; it had actually been only at the second to lowest gear). Everything is fine from that point, provided the shock to my rhythm doesn't completely toast my climb! (I'm grunting when I'm down this low in my range of gears!)
I've had the chain measured to see if it has stretched; it appears to be within an acceptable range. Is there something else that might be causing this? I thought it might be a problem needing adjustment of the indexing, but having read about indexing, I begin to doubt that is the problem. Any suggestions? rcd