When the power steering rack-and-pinion is part of the steering system, the rack has a slightly different design. Part of the rack contains a cylinder with a piston in the middle of it. The piston is connected to the rack. There are two power steering fluid ports, one on either side of the piston. Supplying higher-pressure fluid to one side of the piston forces the piston to move, which in turn moves the rack, providing the power steering assist. Rack-and-pinion steering is quickly becoming the most common type of steering on cars, small trucks and SUVs. It is actually a pretty simple mechanism. A rack-and-pinion gearset is enclosed in a metal tube, with each end of the rack protruding from the tube. A rod, called a tie rod, connects to each end of the rack. The pinion gear is attached to the steering shaft. When you turn the steering wheel, the gear spins, moving the rack back and forth. The tie rod at each end of the rack connects to the steering arm on the spindle. The rack-and-pinion gearset does two things:
It converts the rotational motion of the steering wheel into the linear motion needed to turn the wheels. It also provides a gear reduction, making it easier to turn the wheels. On most cars, it takes three to four complete revolutions of the steering wheel to make the wheels turn from far left to far right.
Generally, lighter, sportier cars have lower steering ratios than larger cars and trucks. The lower ratio gives the steering a quicker response — so, you don’t have to turn the steering wheel as much to get the wheels to turn a given distance — which is a desirable trait in sports cars. These smaller cars are light enough that even with the lower ratio, the effort required to turn the steering wheel is not excessive at all.