QUOTE: Originally posted by doctorwayne For most freight cars up to 70 tons, 33" wheels are correct, while 100 ton cars and those heavier generally use 36", although there may be exceptions to both types. Another thing to watch for with some trucks is axle length: the axle length of the replacement wheelsets should be similar to that of the stock wheels. If you're going to the trouble of changing out the wheelsets, it's a good time to use a "truck tuner" tool to clean up the bearing holes in the sideframes at the same time. In fact, even with the stock wheels, the tuner can improve rolling qualities. They're available at any good hobby shop or from MicroMark. Wayne