What is the correct wheel diameter for tank cars? I thought tank cars used 36" wheels.
A modern roller bearing truck would probably have 36" wheels. Older trucks could have had 33" or 36", depending on the era.
Wheel diameter was usually based on weight, a car with a capacity of 77 tons would use 33" wheels, 100 Tons - 36" wheels and 125 Tons - 38" Wheels.
I would try to find the prototype plans in various model magazines in order to have the correct wheel diameters.
Rick