What was the last year that cars had 6-lug wheels? Standard 1948 car wheels were 16" and had 6 lugs (15" 6-lug car wheels where also available this year).

As Bill posted, during all Advance-Design years, 6-lug 15" wheels were available on 1/2 ton trucks; however, the 15" wheels were optional and the 16" wheels (6.00x16", for all years) were standard (at least on USA trucks: 1948 truck wheels and 1954 truck wheels).