I am using 24" radius curves on my mainline, No. 6 turnouts and 2% maximum grades. How many cars should I be able to pull? I am having trouble pulling more than about 15 cars with a single Athern
SD40 (20 yrs old).
For that particular engine, that's probably just about right, although you can improve it with extra weight. You can add weight while holding the locomotive still with the wheels slipping until you
reach just shy the maximum current rating for the motor. For a 20 year old Athearn, I would stop at a little over half an amp on your ammeter. If you don't have an ammeter, listen to the motor spin
VERY carefully as you add weight, if it starts to slow down at all, you've reached the limit, and back off a little. We have gotten stock Athearns of that vintage to the point where they will pull
about 40 cars on straight and level track. Even my P-2000 BL-2 starts to have a little wheel slip with 15 relatively heavy (3-3 1/2 oz) cars on a 3% grade.
On 24" curves and 2% grades, you'll probably want to limit total length to about 50 cars, otherwise you start to get problems with the cars being pulled sideways off the track on the curves, although
there really is no practical limit. On smaller layouts we've run trains of 100 plus cars where the caboose is about two feet in front of the locomotive! It really depends on the layout and how many
powered units you have on the point.
I will mention that over about 150 cars (depending on the weights) you also start to have to worry about pulling drawbars (breaking the coupler, or at minimum pulling it right out of the pocket).
Don Dellmann