Suspension Systems Designs

In a car with independent suspension, each individual wheel moves up or down independently without affecting other wheels. There are two main independent suspension designs:

• Double-arm control uses two triangular control arms, one above and one below each wheel, to attach it to the chassis. The arms move vertically, and ball joints with spindles attach both arms to the wheel hub. Between each lower control arm and the underside of the frame is a coil spring wrapped around a shock absorber; the two work together to smooth the car’s ride over even the bumpiest of roads.
• McPherson strut—not to be confused with a dance move—is a design common on European vehicles. It uses a single control arm that is attached to the lower side of the steering knuckle. A weight-bearing strut and coil spring are attached directly to the top of the steering knuckle.

Both double-arm and the McPherson suspensions use sway bars to transfer movement from one side of the car to the other to prevent it from flipping over in a turn. The sway bars are attached to the chassis by sway bar end links and sway bar bushings.

The second design, a live (solid) axle, moves up and down like a see-saw, affecting the height of the wheel on the opposite side. Although less adept at maintaining traction, this type of suspension is stronger and more common on rear axles, and is especially common on trucks.

Live axle designs commonly use leaf springs rather than coil springs, shocks, or struts. Although this arrangement doesn’t effectively provide a comfortable ride, it better distributes loads evenly, which is why this type of suspension is generally found on trucks and larger vehicles.

Steering

Most cars use a rack-and-pinion steering system in which the steering wheel turns a steering shaft that is connected to a pinion gear. This gear moves a steering rack left and right. The rack has two arms attached to it called tie rods, which connect to the steering arm and steer the wheels.

Recirculating-ball steering, often found on larger vehicles, has a design much like a nut and bolt. The bolt is a worm gear, which is attached to the steering shaft. But unlike a bolt, when the worm gear turns, it remains stationary. The nut, or ball nut rack, is a threaded block that moves forward and backward. The ball nut rack is connected to a pitman arm, which moves tie rods to turn the front wheels. Between the threaded block of the ball nut rack and the worm gear are little steel balls, which recirculate to reduce friction and wear, and remove slop from the steering.

Power steering can be found in both systems. It uses hydraulic power to provide mechanical assistance to steer the vehicle. Power steering systems use belt-driven pump and pressurized steering fluid carried through hoses to push a cylinder and exert extra force on the steering rack. It makes moving the wheels almost effortless for a driver.