As a follow-up, I'm in the process of tuning up the limited rolling stock I inherited, plus recent additions of used cars purchased at a local train show. After making sure everything had Kadee couplers, and metal wheels, I went through the process of verifying car weighting using NMRA standards (for HO). My cars are all from the 80's and 90's, and are mostly Athearn or Roundhouse, with a couple of Life-Like/Model Power, or Accurail thrown in, while some are unidentified brands. Some I upgraded for purely sentimental reasons. The fleet is mainly 40' boxcars, 33' open hoppers, 54/55' covered hoppers, with a flat car, 37' tank car, and gondolas. In total there are 20 cars plus a caboose. Based on NMRA standards, my fleet should have weighed in at 79.97oz, but came in at 64.02oz, a shortfall of 15.95oz. Using 1/4oz stick on wheel weights (Amazon), I was able to add 13oz in total. I did not add weight to the flatcar, tank car or caboose. 2 cars were originally at, or slightly above, the NMRA standard and required no additional weight. The added weight was divided by the remaining 16 cars. Some required 1/4oz while one required 1.75oz. The rest fell in between. I was worried if my old GP50 could pull the additional weight, so as an experiment, I kept adding cars and testing. Surprisingly, the GP50 (Athearn circa 1987) pulled my dummy GP38, all 20 cars plus the caboose with relative ease on my flat (other than warpage) 4 x 8 layout. The "train" 3/4 fills my outer mainline. Any longer, and the crew in the caboose would be eating with the engineer in the cab. lol I never intend to run that long a train, and my future layout (still a 4 x8) will have a switching yard so the cars will have lots of track to spread out on. For those with older fleets, it's never a bad time to check car weighting as there's likely a lot of underweight cars out there.