"Bob M" wrote:
Now, I've confirmed this -- the front chainrings really are wobbling. I
put cardboard up against the downtube and put a line on it. The large
chainring wobbles inside the line and outside the line with each complete
turn of the cranks. The largest travel (farthest from the downtube)
appears to coincide with the drive side crank; the smallest at the other
end (when the non-drive side crank would be aligned with the paper). The
amount of wobble is small; about 1/16 inch, but it's enough to affect
shifting. I've confirmed this by comparing the distance from the
non-drive side crank to the downtube and the distance from the drive-side
crank to the downtube (former smaller than latter).

What could cause chainring wobble? The crankset and bottom bracket are
both new. Could the bottom bracket be crooked relative to the downtube?
I do not see any metal breaks or anything other type of broken frame parts
-- the frame looks darn new.

Thanks.

--
Bob M
remove ".x" to reply

Do the crankarms actually wobble, or just the rings?

I've corrected misallignment caused by bent chaingrings by carefully tweaking
the rings with a large adjustable wrench until they are laterally true, with
good results. Desired result: Rings are flat and perpendicular to the bottom
bracket spindle and parallel to each other.

If plane described by the sweep of the crankarms is not parallel to frame
then...?

--
Mykal C