Ok, just to clarify.
Over run, you said that "So a 4 wheels unit off a Boeing 747, with say 20 t per wheel, is 80 tonnes on the leg. This is equivalent to a loading by 2.25 * 20 = 45 tonnes on a single wheel on the leg"
Does that mean if the leg only had one wheel, it would be exerting a load of 45T on the ground? However, if there were 4 wheels, there would only be a load of 20T on the ground from each wheel.