Wide tire on Night Train

I want to put a wider tire on my 01 Night Train but would like to avoid the costly wide tire kit and stick with my stock fender and swingarm. Can anyone tell me how wide i can go with the stock parts and what kinds of easy mods I could make to go a little wider.
Thanks

 

You might start here
http://www.us.metzelermoto.com/product_info/upgrade/stage_1/index.htm

 

I had an oversized tire on the back of my roadking and when I replced it I went back to the smaller tire. I had a 130 front and a 140 back and when I went back to the 130 back I noticed an improvement in handling instantly. Just for your information.