Looks like just enough wideness. How many miles on the old one?
When I bought my '72 Bonneville years ago, it had a 16" rear wheel with a fat tire [not sure, maybe 5 inch?]. The guy had it a bit harleyized, high handlebar, sissy bar, corbin seat. Rode it like that for a while and it was ok until spokes broke in the rear. Traded the 16" for a stock wheel and new tire put on a low handle bar and what a difference in handling! Much better, a hell of a lot better.
Is there an advantage to a fatter tire? They look cool.