Originally Posted by
HillRider
What's the frame? Some older frames were laterally flexible enough that the rear triangle would move sideways under chain tension enough to cause a shift. Closely spaced cogs like 9 or 10 speed made this more of a problem.
I can verify this from experience. I have an old Bridgestone Radac (basically a Japanese Vitus, bonded aluminum). 8sp worked fine on it but I get ghost shifts with 9sp.