I had 16.5 on my 85 W350. I went up to the 17" wheels. Lots of nice radial options out there for the newer trucks that are using 17's. If you want aftermarket wheels the sky is the limit for options. But is you are looking for a stock look, i know guys that are using the 16" wheels off the Ford E series van. I believe they are a wider rim. Maybe 7". My dads 90 W250 had a 16x6 wheel from the factory.