Guys,Here is the other side of the coin.. I have been in the hobby for 52 years and yet to weigh my cars to RP20.1 I have found the extra weight is not needed with todays quality cars such as Athearn,Accurail,MDC and other like brands of cars and never had a problem.The club that I go to does not follow RP20.1.The only exception would be the Impact cars,front runners and road railers as these cars are indeed on the light side still it is not to RP20.1. We run 50 car trains as the norm without problems..BTW the reason we run 50 car trains is that is what will fit our passing sidings with 3-5 locos and caboose... Remember when you add the extra weight you put more strain on you locos going up grade and down grade( the added weight will push against the engine gears going down grade....Plus you cut the pulling power of your locomotive down.. Again this is the other side of the coin and meant to be food for thought. RP20.1 came along during the era of wooden car kits and light weight plastic cars .The Varney line of plastic cars comes to mind.There where others as well.