I haven't looked at the charts yet, but ApeG, I believe the maximum gross load capacity of the ML is much higher than that of the S. That must have something to do with it. Also, the load distribution on the tires for the all whell drive truck is very different from the cushy ride suspension geometry of the S class. Thus, though both vehicles weight approximately the same, the ML rims is designed to accomodate a vastly larger range of load distribution, even under normal driving.