Originally Posted by
NeilGunton
Shimmy is very complicated, it has many variables that figure into it, but my intuition is that the stiffer frame will help to stop the inherent flex in the frame setting up the resonant wobble that eventually becomes shimmy.
One experiment with $20000 worth of test equipment is all that is required to prove your intuition wrong in this case. Below the first resonant frequency of a structure, you will not get any vibration in the structure itself. It acts as a rigid body -- you're just shaking the frame back and forth with the fork/wheel. So changing the tubing would have no effect until you made it into a wet noodle. The wet noodle wouldn't ride well enough to even consider as a bike.