I have a 150 tire on my bike right now as we speak. I think that is as large as you can go safely when your tire heats up it won't hit the chain.
79 LTD B3
80 LTD B4 1075 kit JE Pistons .410 cam grind, Bassani, 31 keihin CR Specials...
1980 Z1R, 2002 ZRX1200, 2003 ZRX1200