A pre-existing trailer is modified to increase its payload capacity from approximately 50 tons to approximately 60 tons. Modifications involve the addition of one new axle, and the remounting of existing wheels to make them steerable. The modified trailer has one fixed axis axle and four steerable axles (two in front of the fixed axis axle, and two behind the fixed axis axle). During turning maneuvers the ground wheels on the fixed axis axle turn freely without skidding because the other steerable wheels automatically turn into the direction of steer. The modified trailer operates with lessened skid force on the wheels, with resultant increases in tire life and axle life.