The invention is a high inertia flywheel for a tub grinder to stabilize the rotational speed of a hammermill of the tub grinder and to act to prevent jamming of the tub grinder. A high inertia flywheel attached to either the input or output shaft of the hammermill and outside the confines of the tub. A slip clutch or fluid coupling interconnects the flywheel to the hammermill. A motor spins the flywheel to a desired speed before the clutch is engages or disengaged. A control is used for adjusting the connection between the motor means and the flywheel.