Independent suspension: The Focus' rear wheels are kept on track by a diamond-shaped wishbone axle. Each wheel reacts to the road independently and springs up and down simultaneously thanks to the rear axle's special kinematics.
The chassis of your Focus ensures good driving characteristics and ride comfort. In theory, it should guide the wheels precisely in all possible situations, on a wide variety of surfaces and with every movement. This is the theory; in practice, this means finding a compromise that is as close as possible to the theoretical ideal. The usual practical search for the theoretical ideal keeps powerful industrial computers and numerous vehicle testers around the globe in suspense. Since the wheels of your Focus must not only rotate, they must also move up and down as unnoticeably as possible while driving. Also, when braking, accelerating and turning, various forces arise that significantly load the chassis. The work becomes collective only when all the elements are precisely harmonized with each other. The chassis includes springs and shock absorbers, suspension of the wheels of the front and rear axles, steering, as well as wheels and tires. The brakes - also an element of the chassis - are described in a separate chapter.
Calculating the chassis is a whole science
Well-designed wheel suspensions are a science even in the computer age: the wheels must always be at a precise angle to the car's axle. But if you drive your Focus over a bump in the road or take a turn in a hurry, the geometry of the wheel inevitably changes. The wheels must never lose contact with the road - your Focus, following centrifugal force, seeks the shortest route to the "offside". To prevent this from happening, if possible, the wheels are sprung relative to the body. The suspension dampens shocks and smooths out the road surface. To prevent the body from vibrating and swinging undesirably, it is calmed by a shock absorber on each wheel. Shock absorbers should actually be called vibration dampers: they do not cushion shocks, but dampen the natural vibrations of the springs.