I have a lifelike loco that frequently derails. I have taken a close look at what happens when it derails, and it appears the torque of the drivingwheels is lifting the bogie they are part of. As a result the forward most set of wheels (depending on the direction of travel) lift up to the point where their flanges leave the track. The problem is most apparent if the loco is pushing a train, or for some reason has a bit more than normal load (eg an extra long train or pulling up an incline). Without a train attached it can run over my track at any speed no problems whatsoever (although watching it closely the wheels will lift a little, but not enough to derail). I'm inclined to think that this would be caused by the loco being too light or not having enough of it's weight over the driving wheels - would this be a pretty safe assumption?