Middle management
Q The advent of the new C8 Corvette with its mid mounted engine [see page 8] has inspired some comments on the handling characteristics of such cars. To quote: ‘A mid-engine car has a low polar moment of inertia, allowing the car to change direction more easily’, but ‘it can be harder for a novice to recover should the tail break loose’. The second quote seems problematic or unclear. It would seem that the low moment of inertia, and relatively high ratio of wheel torques to inertia, that enable the mid-engine car to change direction easily should also allow control to be regained more easily in a skid.
Is this reasoning flawed? Or is the qualification of ‘novice’ here relevant? Would a pro not have the same problem? The central driver location would reduce the driver’s lateral motion in a skid relative to a more rearward location, so that inertial information of a skid might be reduced, but the visual and inertial cues from rotation should be the same. Does the ‘harder to recover’ statement agree with reality?
It is certainly correct that a car with centralised masses will change direction more readily
THE CONSULTANT
A The polar moment of inertia referred to here is a measure of the car’s rotational inertia about a vertical () axis. This is expressed mathematically as the radius of gyration, , times the car’s mass. To understand what the radius of gyration is, imagine that all the car’s mass was concentrated at one infinitely dense point, some distance from the centre of rotation we are considering. How far away would that notional single mass need to be, to have the same rotational inertia the car has? Stated another way, the car’s mass, times the radius of gyration squared, times rotational acceleration, equals rotational inertia.
