78 kz 650 c2 back tire???????

hi there i as building a 1978 kz 650 c2 stock aluminum rear wheel...what are my tire size options...i would like to go a little widder any suggestions ho big or wide can you go??? thanks

Welcome.
130 is the widest that will fit on a stock C2 back wheel.
I have had a 130 on for years, but am thinking of switching to a 120 as some say it handles better with the 120.
Plus that's what Kawi engineers thought too.

You can go up tp 130/90-18 if you modify or remove the stock chain guard, I ran that size for years on my KZ650C1, BUT I don't recommend it. I switched to 120/90-18 and found that the tire is much less deformed because it isn't squeezed on that narrow rim. So it retains a better profile and in my opinion works as well or better than the 130. I highly recommend the Pirelli Sport Demon tires! They're a bias tire with a modern, radial-like tread pattern and they work well on the KZ650. Ed

thanks guys could you go with a 120 80 18 a little shorter

The 80 is a little shorter but your engine will run at a little higher RPM on the highway (assuming stock sprockets).