A new method for measuring the inertia tensor of rigid bodies has been developed and applied. A new test-rig, based on the developed method, has been built. The test-rig is basically a three- or four-bar pendulum, carrying the rigid body under investigation. The pendulum is excited either by well defined initial conditions or by a harmonic force. The spatial motion of the pendulum is highly non linear and is recorded by means of accelerometers and gyroscopes. The components of the inertia tensor are identified by a proper numerical procedure which makes use of a mathematical model describing the motion of the pendulum. A proof of the convergence of the identification procedure is given. A validation of the measuring procedure is presented. The maximum error on the main diagonal components of the inertia tensor is less than 0.7%. Further improvements on the precision of the measurement procedure are possible. The rig has been used to measure the inertia tensor of a number of road vehicles and other bodies.