daestrom wrote:

But the trouble with overall weight is the combination of weight, power
and rail capacity. When you get to larger units, the rail used on a lot
of roads can't handle more than about 50,000 lbm per wheel set. That
means you're limited to about 100 tons for a unit with just 2 axles per
truck (4 total). Go up to a 120 ton and you need 3 axles per truck.
But a 100 ton, 4-axle unit has 12,500 lbm per axle, while a 120 ton,
6-axle unit has only 10,000 lbm per axle. If the wheel friction
coefficients are the same, the 4-axle unit can develop 25% more tractive
effort when starting before slipping wheels.

lbm?

I'm not sure on your units.

In another life I used to calibrate railroad electronic weigh bridges.

4 axle locomotives were about 265,000 pounds (US).

6 axle locomotives were about 360,000 pounds.

One 3 axle drive truck weighed 65,000 pounds.
(In a second other life, hauled it on a flatbed truck.)