This may seem like a self serving question but here we go.
I am not a tire expert but from what I have seen or heard the way to improve
handling on a vehicle is to increase wheel size (like with 15" alloy wheels)
and then go for a lower profile tire (like 205/60s).  Is this true?  I know
that lower profile tires would not be so good in adverse conditions (like
going through the woods or on really bumpy roads) but my driving very rarely
sees any conditions like these.  I figure that lower profile tires should
really help with the swaying and wind buffeting that Vanagons and Westies
experience in windy condtions.
Why is this self serving?  Check out my website at www.vanagain.com and you'll
find out.
Ken Wilford
Van-Again
John 3:16