36"

The big grain hoppers are 100-ton cars, per the CAPY line in their data.   So they need 36" wheels.  This usually brings the couplers up to correct height while you're at it. 

And if you're looking for more info on the prototypes for that Athearn model, it's a Pullman-Standard PS-2 4740 cubic footer, PS-2/4740 for short.   Covered hoppers are not usually referred to by their length, but by their volume.  Neither are tank cars, except on the ends of Athearn boxes....

Scott Chatfield 

Wheels

Would the walthers proto 36" wheels work with the athearn trucks?

I have made them work

I have made them work before.

Get the MicroMark Truck Tuner and use it while you are replacing the wheelsets. Makes a big difference!

Rule of thumb

100 ton cars 36-inch; 70 tons 33-inch, There are exceptions such as triple deck auto carriers being 28-inch.