i am having a hard time figuring out if i am hauling within my load limits without actually getting on a scale; i have hauled approx. 4000 lb. of rock in the bed of truck with another 1000 lb. s in a trailer (probably another 400# tongue weight) and the rear axle rates at about 7300 lbs. . How much curb weight is on the rear unloaded and how much of an evenly distributed bed load weigh on each axle approximately (percentage-wise). Any advice would be appreciated