The load carrying ability is normally dictated by the vehicle load rating. Most Utes sold in Australia have a load capacity of about 1 ton. Bocar Deluxe and Ultimate alloy ute trays are manufactured with floor rating of 2.5 ton, so there is no problem in terms of loading.
In fact, using an Alloy Tray, the load capacity is higher than when using a Steel Tray. A typical alloy tray weighs about 100Kg and hence can carry a load of about 900 Kg on a vehicle with a 1 ton capacity. In contrast you can only load about 700 Kg on the same vehicle fitted with a steel tray, as the steel tray weights about 250 to 300Kg.
