Front Tire: whats the max size can upgrade to? 130's.....and if this is possible, how will it affect the performace of the bike?

Rear Tire: Whats the max size can upgrade to without major mods? ie, getting a new rim

again 

http://cgi.stanford.edu/~sanjayd/gs500/

a 120 is THE WIDEST you will be safe going to on the front.   on the back, a 140 should fit right up, POSSIBLY a 150, but you may have to work for it with the 3.5" rim. ABSOLUTELY NO WIDER than a 150 rear.  anything wider will pinch and have a negative effect on handling as the tire's profile becomes distorted.

Quote from: bobthebiker on November 09, 2008, 04:44:24 PM
a 120 is THE WIDEST you will be safe going to on the front.   on the back, a 140 should fit right up, POSSIBLY a 150, but you may have to work for it with the 3.5" rim. ABSOLUTELY NO WIDER than a 150 rear.  anything wider will pinch and have a negative effect on handling as the tire's profile becomes distorted.

Wait so what is the rim size stock? and whats the max width the rim will take?  150??

the stock GS500 wheel is a 3.5" rim,  but there is a Katana 600 rim off the 98 and newer models that will fit up allowing a 160 rear tire on the 4.5" rim that the 98+ katanas come with.

the 150 rear tire may be pushing it, but I know for a fact that a 140 will fit safely.   the 150 should be something like a 150/60/17 rear.   the front I like running is a 120/70/17 personally.

I'll probably up it to a 140 when it's time to get new tires for the rear.