I have Cooper Tire SRM II LT215/85R16 black truck radials on my Suburban (they are pretty old, 10+ years).
The 1954 16" rims are 4.5" x 16".
Your 1947/48 rims might be either 4.0" or 4.5".
The mounted tire diameter, as Carl posted, is around 31". The "advertised" diameter is around 28".
