I don't think having an extra trailer figures in the load capacity as much as the number of axles in the case of TELS.
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I don't understand that you want to say.
Two times heavier ICBM won't be two times longer, maybe 30-40%.
The per axle weight has to be the same, so the length of the vehicle can change, proportionally to the load, so an 80 tons ICBM will be two times longer than the Topol-M. But the length of the missile will be smaller than this, but the centre of gravity will stay, just to complicate the things.
But if the truck is a single unit then the turning radius of it will be extreme, so it won't be able to move on the Chinese road network, only off-road.
The reason why all very heavy truck is trailer-multi car configuration is to keep the turning radius within the design limits of the roads.
Even if it is multi-truck configuration to have a load this long, big and sensitive it needs a complex beam structure, that increase the height of the truck.
These swept radius for tractor-trailer trucks , so a single unit can be as long as the trailer .