Possible causes of "twitching" in '94 S4?

["Geoff Jenkins" <jenkinsg@pilot.msu.edu>]

I've noticed that the S4 has become twitchy since I fitted 17" rims a few
weeks ago. With the previous 225/50/16's she always tracked perfectly on any
surface. With the 225/45/17's, at speeds of 45-65 it starts to almost seek
out grooves and irregularities in the road. Below 45 it isn't noticeable, at
speeds beyond 65, up to 120, it's stable again. It's also fine on the rare
stretches of well-paved freeway around here at 45-65.

I know wider tires are noted for sometimes causing this, but they're still
225's and only 5% lower profile, so does anyone have any suggestions of what
might cause this, or what changes/modifications might alleviate it?

TIA, Geoff