Four roll-set rolling roads. These machines range from end-of-line rigs consisting of four sets of independent double-roller units, to complex development test rigs, some having steered articulation of each roll unit. The production rigs permit the checking of onboard vehicle control systems, transducers and system wiring by simulation of differential resistance and speeds of rotation. The development of
hybrid vehicles may give impetus to the development of independent four-wheel chassis dynamometers since some designs are based on individual wheel drive motors. Electronically controlled transmission systems on 4×4 vehicles also require this type of dynamometer to simulate the road conditions for which they are designed to compensate.