Wheel size on freight cars. Wheel size on freight car trucks is dictated by the maximum gross weight on rail ( MGWR) for the car, or the the case of articulated cars, the axle loading on the particular truck. 33" wheels carry a MGWR of 220,000 lbs. (70 ton trucks) 36" wheels carry a MGWR 0f 286,000 lbs. (100 ton trucks) 38" wheels carry a MGWR of 315,000 lbs. (125 ton trucks) Since wheel size normally also has a specific bearing size, exceptions are made for smaller wheels, like 28", for clearance purposes as long as the larger bearings are used. On an articulated stack platform, you can see that the end trucks bear half the weight of 2 containers, while the interior, articulated trucks, bear half the weight of 4 containers each, hence the 33"-38" wheel difference. The end trucks are 70 ton trucks, while the articulated trucks are 125 ton trucks. :cat:
