In a method for controlling a traction system for a heavy road vehicle, the system includes a first mechanical propulsion system, a second hydraulic propulsion system, and a control unit. The method includes measuring a first parameter value, indicative of the rolling radius of a first traction wheel, measuring a second parameter value, indicative of the rolling radius of a second traction wheel, and the control unit using the first and second parameter values for determining a present relation between the rolling radii of the first and second traction wheels. The control unit provides an output signal based on the present relation to optimize the traction applied to the second traction wheel. A traction system and a heavy vehicle incorporating a traction system are also provided.