[A4] Question on tire size and handling

[gsackerson@comcast.net]

Hi all,
  Could someone explain to me the fundamental driving characteristics of a larger tire vs a smaller one? I realize there are tires with different profiles, but what I'm referring to is how the same make and model tire would handle in a 17" tire (what is coming on the 2006 A4 I just purchased,) vs. let's say a 16" (what is on the 2002 A4 I currently have.) The 2006 A4 comes standard with 16" tires, but I get the impression if I'm not mistaken that you can go all the way to an 18" tire, yes? Since I live in Colorado, clearance for snow is important, and secondly, since I commute 30 miles each way, most of my driving is highway miles where comfort is as important as handling. 
  So, I'm interested to know what I can expect to be different when going to the 17" tires other than having to spend more for tires! Thanks for your feedback...

Glenn