I have a group of new hopper cars and the are bigger and longer than my old cars. One part of my layout they run fine and then the other part they derail. At the turnouts they dont do good either. My old cars ran fine. The turns in aren’t that bad at all. I think its because of the new wheels or they are wider. Is there a difference in rail height or width. I dont know if there really is. I hope I dont have to take it up and put new track down.
the newer cars might have RP25 wheels on them, with smaller (i think prototyipcal) flanges, so they might just be showing you where you have out of gauge trackwor, or some of the wheels themselves might be out of gauge
Make sure your wheels are in gauge and make sure the coupler trip pins aren’t too low and dragging when passing over turnouts. These are the two major causes of derailments.