Definition of running gear:
(n) :
(automotive) The wheels, suspension, steering, powertrain and usually the chassis of a motor vehicle.
(n) :
(railways) Those components of a railway vehicle that run passively on the rails, unlike those of the driving gear. Traditionally these are the wheels, axles, axle boxes, springs and vehicle frame.
(n) :
(historical) The wheels and axles of a carriage or other vehicle.