On a brand new empty unit coal train of otherwise identical cars, I noticed that the Load Limit for each car varied over a range of about 1000 pounds. The numbers were rounded off to the nearest hundred pounds, but even on consecutive car numbers the variance was present. The cars had brand new trucks, bearings, and wheels - not a flat spot on the whole train. I realize there will be variances in manufactiring, but how are these numbers assigned? Do they actually weigh each car? Does the loader at the mine care and how do they load trains of mixed cars?
Yes they weigh each car to determine light weight and load limit.
Mac
Yes, the weight of the cars is critical. If you see this train again, just for fun, add the load limit and the light weight. The sum will always be the same–286,000 pounds. That figure–the Gross Rail Load–is the real critical number.
Maybe somebody who knows about the loading operations can enlighten us as to how closely the load limit is aimed for–it should never be exceeded, of course.
The tolerance is less than 1,000 pounds. Also, each time the cars are shopped they will be reweighed to see if the light weight has changed.
OK, so what would cause such a variant in factory weight? I would think the manufactuers would not want such a variable. I would understand it after shop visits and road abuse, but aren’t rail cars produced to spec enough that there would not be 500 or 1000 lb. differences?
The aluminum parts of the cars are pretty close but the cast iron trucks and steel center sills may vary by quite a bit. Don’t worry too much, they generally just load in the same amount of coal into all the cars in the train and let over engineering handle the overloads.
Look at it this way, 1000 lbs is 1/2 ton on a 143 ton car with load. The variance is about one third of a percent of the total weight of the car with load which is pretty insignificant in the scheme of things.