tire size/ gs swingarm

I have a 77kz1000 with a 81 gs1100 swingarm and an aftermarket 18in wheel that I believe to be 4.25in wide. Does anyone know if I can use a 150-70 tire, why should I or should I not go with the wider tire? Avon makes the tire in 130,140,or 150. Any help would be appreciated

If you measure from the centerline of your current tyre (or wheel rim) , with all the spacers etc in place, to the chain,that should give you an idea of how far you can go with a fatter tyre.

A 150 should fit fine inside that swingarm. Be sure to check tire to chain clearance though, and chain line.