I'm using fishing sinkers. They tell you how much they weigh right on it. and I am sticking about 2 oz on each truck if the unit is long enough to support it. My reasoning is because I am tired of all the derailements at the switches and curves. This makes them hold the track well. I just pop the shell off and use Elmer's glue to secure the weights. I am not using model cement with that because the Elmer's glue can get cleaned up easily and the model cement can't. a 4 oz unit plus whatever it weighs without the added weights. I am not as concerend about the weights because my units are not going to a competition like a pine car race where the weight is of importance. If you loco can't pull it maybe it needs more weight? Mine do very well, with an average of 15 boxcars.