Originally Posted by
dasding
my original question was probably phrased in a stupid way: I realize that it isn't normal for the wheel to hit the stay, so I guess I'm wondering if
a) it is a common problem with Al frames and a sign that the frame is wearing out
Nope on this one. Frames do not get softer as they wear out. If anything, they would get stiffer right before cracking.
Originally Posted by
dasding
b) can be attributed to a crack somewhere that I need to look for (not quite sure how/where they appear)
This is more likely. Look at where the rear-dropouts attach to the chainstays. Also where the chainstays meet the bottom-bracket shell.
Originally Posted by
dasding
c) it could be a problem with the wheel other than dish--like can the wheel flex if the spokes are not tensioned properly.
This is the most likely area. Although the actual amount of flex caused by human pedaling-forces are puny, it is possible to flex a wheel by standing and rocking the bike away from vertical, thus using your weight to bend the wheel sideways. Another idea is loose wheel bearings. Rock the rim back and forth between the brake-pads. Do you see and feel movement with a >clunk< at the end of the movement range?