Three–axle buses: a solution for reducing axle load

The need to reduce axle load has led to the increasing use of the third axle on buses and coaches. Disadvantages include extra cost, higher operating and maintenance costs, and increased noise. Various methods of installing the third axle are discussed. Technical problems involved in installing the third axle include: finding an optimum steering angle, wheelbase, rear and front overhang and wheelbase for the double axle; finding the optimal axle–load distribution; calculating the modified load distribution for the frame, the extra load on the frame when the trailer axle is unloaded; and controlling the air pressure in the air springs. Simplified two–axle and three–axle models in the form of a lattice–type frame were used to simulate the bending moment distribution. Results show that, by using the third axle, maximum bending decreases on the sidewalls and longitudinal members of the frame.