Just did an impromptu, unscientific test on 3 cars, a Gilbert 937, a 937 equipped with the brass axle bushings and an SHS SF reefer. On parallel tracks with the 937's side by side, I propelled the cars with a piece of plastic spanning the ends of both cars. I applied a light shove for several inches and let the cars roll to a stop. I performed the test about 10-15 times to get an average roll out. Both cars were freshly oiled. The bushing equipped 937 consistently rolled 1/2 to 1 full car length further before stopping. The more force applied, the further the gap widened. The SHS reefer was then compared to the Bushing equipped 937 and at minimum force exceeded the 937 by 3-4 car lengths. I then compared a string of 10 various Gilbert cars to 10 bushing equipped Gilbert cars by trying (unscientifically) to pull on the lead cars knuckle to gauge the force needed to move the cars. The bushing equipped string moved with far less force. I would translate that to an ability of an engine to pull more cars with less exertion. The SHS rolling advantage is probably due to the smaller (conical) axle contact point and the narrower metal wheel contact surface on the rail. A lot of Gilbert axle holes are larger or irregular due to wear and machining and the bushing appears to restrict the axle from excess movement within the journal hole. I feel the bushing equipped cars operate better than the Gilbert trucks and are worth the $2. Are they as good as SHS/AM axles, no.