Paul, model trains do not perform like real trains.
For one example, the weight of the car on the rail
is distributed over an area larger by a factor of 87.1.
(The surface area of contact between the wheel and
rail only changes in 2 dimensions as you scale down.)
Also, our curvature is usually about 10 times as sharp
as you'd find on a prototype. If you put 1 oz cars with
5 oz cars in a train and run it up a 3% grade with 40
degree curves, then don't be surprised when you get
"stringlining" of cars in the middle of the train.
There must be a FAQ out there somewhere... try the
LDSIG mailing list.