Anti roll bar.

It also resists roll in corners, helping to keep the car and more importantly the wheels nearer to vertical. As the car rolls the suspension on the outside compresses and on the inside it extends, the bar twists to resist the suspension movement. It doesn't actually transfer weight from the wheel it just evens out the force applied to the springs. Some of the force that is trying to compress the outside wheel's spring is transferred to compress the inside wheel's spring.

Very few cars don't have anti roll bars. Lotus Elise being one but even the 340R derivative got a front anti roll bar.

You can get away without them on nice smooth tracks in low light sports cars, but need them on modern tall family cars, MPV's, SUV's etc.

When it comes to UK roads I'll take slightly softer independent suspension and an anti roll bar to stiffen up the roll resistance even on a low car.

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An anti roll bar has got 2 functions, the first of all it increases the suspension stiffness in roll by transfering force from outer wheel to the inner wheel, this way of increasing in roll stiffnes has a less detrimental effect on ride quality over a "2 wheel bump" than the oalternative of simply fitting stiffer springs. Reducing roll is important particularly where wide wheels/tyres are used as with less roll the tyre treads remain square to the road giving more effective contact area and more grip.

The second function is fine tune the understeeer oversteer characteristics of a car; by increasing the roll stiffness at one end of a vehicle grip can transfered to the other end --- stiffening or fitting an anti-roll bar to the rear of a fwd car will reduce understeer and improve traction out of corners. This is because down load (weight) is transfered from the inside rear wheel to the inside front wheel.

Or you could look at it by saying a roll bar *reduces* the grip of the end it's fitted to...