My 1959 GMC had 275/60R15 tires on all 4 corners when I got it. I changed the rims and tires to 31X10.5 tires on 4x4 rally wheels.
My opinion first and second series is only useful when identifying early and late production 1955 trucks. There are way too many differences between the 1955.2 and 1956 gmc trucks to call them the same truck. Here are some of the differences between 1955.2 and 1956 gmc trucks:
1955 gmc trucks with a 6 cylinder were 6 volts and used the gmc 248.
1956 gmc trucks with a 6 cylinder were 12 volts and used the gmc 270.
1955.2 gmc v8 trucks used the pontiac 287
1956 gmc v8 trucks used the pontiac 316.
