Now if this sounds a little cold for you, don't worry, it's not like that at all. A polar moment is all about mass, momentum and force applied at a distance from the centre of the car. Intrigued? Read on...

Simply put, your typical car has a large mass at the front and usually less at the rear. Somewhere between front and rear will be a centre of rotation, i.e. the point around which your car's mass will rotate when cornering. By varying the mass and its distribution, i.e. its distance from the centre of rotation, you are altering the inherent polar moment of inertia of the mass involved and changing the character of the car's reaction to directional changes.

Still confused? The bodywork, the suspension, the interior, the engine - you name it, it has mass. You get that mass swinging and it has a tendency to just keep going. By moving components around, the engine is a good example, a car designer will get a different effect.

If the mass is relatively far from the centre of rotation, and I'm simplifying here, chances are that the car will have a high polar moment. It will be very stable and will react more slowly to changes of steering input. You'll probably imagine a large car here, and that's generally true, although a smaller car can be engineered to have similar characteristics - the Alfa Romeo Alfetta, for instance - where the masses are large at both ends of the car and the small(ish) car twitchiness is counteracted by the high polar moment. So you get a compromise more towards safe, stable handling rather than outright kart-like sportiness.

Speaking of kart-like, if the mass is close to the centre of rotation you get a flighty, nimble, maybe even twitchy car that is said to have a low polar moment. Many people like the nervous feel and it's often to be found in sports cars and, of course, small cars in general. The Toyota MR2 is one example, where the engine is close to the centre (and behind the driver) and the car can be a handful at the limit. In the earlier example of the high polar moment design, the Alfa engineers chose to place the gearbox, final drive and clutch at the rear wheels, to even up the front and rear masses. The resulting weight at each end gives a balanced feel biased towards stability. At the limit the car will slide gently and controllably, something that cannot always be said of the MR2.