http://www.army.mil/article/131126/R...mbat_vehicles/

Operational and tactical mobility could be improved by reducing the design weight of armoured reconnaissance vehicles and early-entry AFVs. Reduction of design weight might also serve to reduce size as a target and also observability. But reducing or limiting the weight of main force AFVs reduces potential armour protection and the weight and bulk of sensors and munitions provided for combat performance and endurance.

Looking on the bright side, researching a blanket 40% reduction in the weight of AFVs might be a usefully memorable exercise in futility.