[blucar]

A basic rule of life that I try to live by is; "Don't let the directions on the can outsmart you"..
Radial tires are made to fit on certain sizes of rims, generally speaking, the minimum rim size is 6", however, many radial tires require a 6.5/7" rim.. Since most antique/old cars have rims as narrow as 3.5", the use of radial tires can be a problem waiting to happen.
On the early Ford trucks, '40-48. the F-1/F100 rim/wheel size can be solved by using wheels from a '59-66 F100.. These wheels came in both 15" & 16" with a rim width in the 5.5/6" range.. The F100 wheels will accept the stock '40-48 car/truck hub caps.
The '47-48 Merc wheels will also be 15" and will accept the '40-48 car/truck hub caps.. Caution should be used on the Merc wheels because they can be narrow, in the 5/5.5" range..
OK, why is the rim width so important? A narrow rim will pull the sidewalls in, resulting in poor road contact of the tread.. It is very important to keep the maximum amount of tread parallel to the road surface for tire life and good traction...