Matt's Automotive

Suspension - Steering Systems
Suspension-Steering Operation


Shock Absorbers

In the past, a wide variety of direct and indirect shock absorbing devices were used to control spring action of passenger cars. Today, direct, double-acting hydraulic shock absorbers and shock absorber struts have almost universal application.

The operating principle of direct-acting hydraulic shock absorbers is in forcing fluid through restricting openings in the valves. This restricted flow serves to slow down and control rapid movement in the car springs as they react to road irregularities. Usually, fluid flow through the pistons is controlled by spring-loaded valves. Hydraulic shock absorber automatically adapt to the severity of the shock. If the axle moves slowly, resistance to the flow of fluid will be light. If the axle movement is rapid or violent, the resistance is stronger, since more time is required to force fluid through the openings. By these actions and reactions, the shock absorbers permit a soft ride over small bumps and provide firm control over spring action for cushioning large bumps. The double-acting units must be effective in both directions because spring rebound can be almost as violent as the original action that compressed the shock absorber.

In the 1930s, there was a school for chauffeurs of the Rolls Royce. Since the car had a reputation to maintain for its smooth and quiet ride, the students had to pass a special test. They were required to drive a Phantom II model with a glass of water on the radiator without spilling a drop!

Coil Springs

Compression type coil springs may be mounted between the lower control arm and spring housing or seat in the frame. Other front suspension systems have the coil springs mounted above the upper control arms, compressed between a pivoting spring seat bolted to the control arm and a spring tower formed in the front end sheet metal. When coil springs are used in both front and rear suspension, three or four control arms are placed between the rear axle housing and the frame to carry driving and brake torque. The lower control arms pivot in the frame members and sometimes support the rear coil springs to provide for up-and-down movement of the axle and wheel assembly.

Leaf Springs

Front leaf springs are used with solid axle beams in most truck applications. Corvettes use single-leaf, filament-wound, glass/epoxy front and rear springs mounted transversely; i.e., they are crosswise to the vehicle's centerline. Rear leaf springs are used on trucks and some passenger cars. Single leaf or multi-leaf springs are usually mounted longitudinally over the front axle beam or under the rear axle housing. The spring center bolt fastens the leaves together, and its head locates the spring in the front axle beam or saddle on the rear axle housing. U-bolts clamp the spring firmly in place and keep it from shifting. Eyebolts, brackets, and shackles attach it to the frame at each end. Leaf springs also serve as control arms, locating the rear end in position and transferring force to the chassis.

MacPherson Strut

In MacPherson Struts, the shock absorber is built into the strut. The strut consists of a shock absorber unit, a coil spring, an upper pivot, and a lower clamp. The upper pivot mounts to the fenderwell. The rest of the unit rotates when the steering is used. The lower clamp secures the spindle and the strut together into a solid unit. Most shock absorber struts are hydraulic units. Some use low-pressure, gas to absorb energy. These are usually nonadjustable and nonrefillable. Like the shock absorber, faulty units must be replaced as an assembly.

Steering Knuckles

The steering knuckle or "spindle" pivots on either a kingpin or on the upper and lower ball joints. The disc brake caliper is attached to the spindle, as well as the tie rod ends and the upper and lower ball joints, or a MacPherson strut bottom clamp maybe attached, instead of an upper ball joint. In rear-wheel drive cars, the front axle (the shaft which supports the wheel bearings) is part of the spindle. Front wheel drive spindles have bearing pockets only.

Torsion Bars

Torsion bar suspension uses the flexibility of a steel bar or tube, twisting lengthwise to provide spring action. Instead of the flexing action of a leaf spring, or the compressing-and-extending action of a coil spring, the torsion bar twists to exert resistance against up-and-down movement. Two rods of spring steel are used in this type of suspension. One end of the bar is fixed solidly to a part of the frame behind the wheel; the other is attached to the lower control arm. As the arm rises and falls with wheel movement, the bar twists and absorbs more of the road shocks before they can reach the body of the car. The bar untwists when the pressure is released, just like a spring rebounding after being compressed.

Adjusting the torsion bars controls the height of the front end of the vehicle. The adjusting bolts are located at the torsion bar anchors in the front crossmember. The inner ends of the lower control arms are bolted to the crossmember and pivot through a bushing.

Struts

A strut is a structural piece designed to resist pressure in the direction of its length. On typical "MacPherson Strut" use, the shock absorber is built into the strut. Most shock absorber struts are hydraulic units. Some MacPherson systems used on Ford vehicles are equipped with low-pressure, gas-filled shock struts. They are nonadjustable and nonrefillable. Like the hydraulic shock struts, faulty units must be replaced as an assembly. Another similar front suspension system is called the "hydraulic shock strut." This strut serves as a shock absorber and replaces the upper control arm. The coil spring, however, is located between the lower control arm and the body structure instead of being mounted directly on the strut.

Tires

A tire is a tubular corded carcass covered with rubber or synthetic rubber, which is mounted on a wheel and inflated to provide traction for moving a vehicle and for assisting the brakes in stopping it. Today`s tires, when properly inflated, will absorb bumps on a road's surface and give a safe, comfortable ride, while providing a reassuring grip on the road at all speeds.

There are two basic types of tire: the tubeless tire for passenger cars and light-duty trucks; and those requiring inner tubes for medium and heavy-duty trucks.

In 1830, Charles Goodyear experimented with turning raw rubber into a more solid and useful product. He bought a load of raw rubber from a shoe factory on credit and couldn't pay. He wound up in debtor's prison and started his experiments. He finished his sentence, and kept on experimenting.

In 1839, Goodyear invited some friends over to a fund-raiser for his experiments. He showed them a ball of rubber that he had hardened on the surface to prove to them that his experiments were worthy of their money. At this point he accidentally threw the rubber ball into the hot wood stove. While he was scraping the ball off with a knife, he realized that the rubber had hardened into just the right texture. This was the start of "vulcanization" and the rubber tire industry.

Tires have changed a great deal since the 1950s. New rubber components have been introduced into tire compounds which improve the skid resistance. Recently new types have been developed to cope with the dangers of sudden deflation. One of the most interesting of these is a tire mounted on a relatively narrow wheel, so that the tire can be run totally deflated without damage to the tire side walls. In addition, the tire contains a special liquid which, when the tire is run under the deflated condition, vaporizes and generates a pressure so that the tire will partially reinflate.

Tire Types and Markings

Size, shape, materials, and construction are all factors that will govern tires' longevity as well as the ride they furnish. The first and most important rule in choosing tires is to follow the directions and recommendations in the owner's manual. Check out the information embossed on the sidewall as well. This information can help the owner choose a set of tires that will suit both the car and the driver's personal needs. The markings on a tire will give the weight (load), size designation, serial number, tire type, carcass cords, DOT, and profile size. Other markings on the tire will probably be the brand name and the name of the tire.

The "size designation" is a combination of one letter and four numbers and is a three-part code.

The letter denotes the sidewall-to-sidewall width of the tire; the two numbers grouped with the letter refer to the height-to-width ratio; and the numbers following the dash indicate in inches the diameter of the wheel rim the tire will fit. To replace the tire, the own will find the sizes that will fit the car specified in the owner's manual.

As to "tire type," government regulations require that every passenger tire be stamped either "tubeless" or "tube-type," but more than 90%% of the passenger cars are tubeless. "Belted" would indicate that a tire has extra strength in its construction. In addition, if the tire were a radial, it would be designated as such - a necessary precaution because radials should not be mixed with other tire types except when the radials are used as the pair on the rear axle.

Bias Ply Tires

There are three general methods of arranging or laying down the tire plies. They may be laid down "on the bias," "on the bias and belted," or "radially."

The standard, and least expensive, tire is a bias ply. In this type of ply, the cord strips are arranged diagonally (i.e., at a bias) to the center line of the tread and alternate plies are reversed to cross at a 30 or 40 degree angle. The result is a uniformly firm body, which will wear satisfactorily at moderate speeds, with sidewalls that can stand curb bruises. In fast driving or hard turning, however, the tread elements squirm together and spring apart, producing heat that weakens the tires.

A veterinarian named John Dunlop in Belfast, Ireland gets credit for inventing the pneumatic tire. In 1888 he tried making better tires for his son's bicycle by using linen-covered sheet rubber. Although he was granted a patent for bicycle and tricycle tires, he sold his idea in 1889. The man he sold it to was named Harvey du Cros, Jr., who started the Dunlop Rubber Company. Dunlop himself was never part of the company.

Tire Rotation

The tire-rotation procedures charted below are not as difficult as they seem. At any given time, only one chart will pertain to any car. First find the number and type of tires you will be rotating. Then read down the column at the left. The top entry on the left is for regular rotation without snow tires. The second and third rows are for snow tire rotation. Remember, if radial tires are used in the front, then the snow tires should be radial also. When storing tires, it is a good idea to record its position on the inner face of each one, using chalk or tape. This will help when remounting the tire.

-------------------------------------------------------------------
                  4 TIRES (Non-radial) Rotation
-------------------------------------------------------------------
   From: R-front to: L-front to: R-rear to: L-rear to: Storage
-------------------------------------------------------------------
 Routine  L-rear      R-rear      R-front    L-front
 Fall     storage     storage     R-front    L-front    R-L:rear
 Spring   L-rear      R-rear      storage    storage    R-L:front
-------------------------------------------------------------------
                  5 Tires (Non-radial) Rotation
-------------------------------------------------------------------
   From: R-front L-front R-rear   L-rear Rear Holding Storage
-------------------------------------------------------------------
 Routine  L-rear   Rear/H   R-front L-front storage      L-R:rear
 Fall     Rear/H   storage  R-front L-front storage      L-R:rear
 Spring   L-front  Rear/H   storage storage R-rear       L-R:rear
-------------------------------------------------------------------
                        4 Radial Tires
-------------------------------------------------------------------
   From: R-front to: L-front to: R-rear to: L-rear to: Storage
-------------------------------------------------------------------
 Routine  R-rear       L-rear       R-front     L-front
 Fall     storage      storage      R-front     L-front   L-R: rear
 Spring   R-rear       L-rear       storage     storage   L-R:front
-------------------------------------------------------------------
                        5 Radial Tires
-------------------------------------------------------------------
   From: R-front L-front R-rear   L-rear Rear Holding Storage
-------------------------------------------------------------------
 Routine  Rear/H   L-rear   R-front L-front   R-rear      L-R:rear
 Fall     Rear/H   storage  R-front L-front   storage     L-R:rear
 Spring   Rear/H   L-rear   storage storage   R-rear      L-R:front
-------------------------------------------------------------------

Static Wheel Balance

"Static" balance is the equal distribution of weight around the wheel and tire assembly. If the unbalance of a wheel lies in the plane of wheel rotation, it is known as static (or kinetic) unbalance. This condition causes the wheels to bounce. The wheel lifts off the road, then slams down during each revolution. This will result in flat spots on the tire tread and worn ball joints, tie rod ends, steering gears, and shock absorbers. Bouncing could also set up a heavy vibration in the chassis and affect the steering balance.

Dynamic Wheel Balance

"Dynamic" balance is the equal distribution of weight on each side of the vertical centerline of the wheel and tire assembly. If unbalance lies on either or both sides of a plane of rotation, it is dynamic unbalance. This causes the wheels to bounce, resulting in flat spots on the tire tread and worn ball joints, tie rod ends, steering gears, and shock absorbers. Dynamic unbalance in the front wheels will cause them to wobble as well. Bouncing could also set up a heavy vibration the chassis and affect the steering balance.

Wheel Balance and Unbalance

It is important to check to see that the wheel and tire assemblies are in balance before aligning the vehicle. "Static" balance is the equal distribution of weight around the wheel and tire assembly. "Dynamic" balance is the equal distribution of weight on each side of the vertical centerline of the wheel and tire assembly. "Unbalance" (or imbalance) exists when the weight is distributed unequally around the horizontal axis of the wheel and tire assembly. Unbalance can exist in the tire, wheel, brake drum or rotor, or even in the hub. It also occurs in any combination of these components. Unbalance can be detected with the aid of special equipment, which usually indicates the proper location for wheel weights to restore the proper balance. Even with regular maintenance, however, uneven tire wear can result from drivers' habits, such as side wear from excessive cornering speeds. To counteract uneven wear that leads to unbalance, the tire industry recommends that tires should be rotated every six to eight thousand miles.

Tire Valves

The tire valve is really an air check that opens under air pressure and closes when pressure is removed. The inner valve or "valve core," acts as a check valve for the air. Positive sealing is provided by the "valve cap," which contains a soft rubber washer or gasket. It is this gasket, pressed against the end of the "valve stem," that seals the air in the tire. The careless practice of operating tires without the valve cap should not be followed, because, without the valve cap in place, there is usually a slow leak of air from the tire, causing the tire to run in an underinflated condition. If air should leak out around the base of the valve, it will be necessary to install a new tire valve assembly. This is easily accomplished with a special lever-type tool.

Sprung and Unsprung Weight

"Sprung" weight is a term used to describe the parts of an automobile that are supported by the front and rear springs. They suspend the vehicle's frame, body, engine, and the power train above the wheels. These are quite heavy assemblies.

The "unsprung" weight includes wheels and tires, brake assemblies, the rear axle assembly, and other structural members not supported by the springs.

Sway Bar

Some cars require stabilizers to steady the chassis against front end roll and sway on turns. Stabilizers are designed to control this centrifugal tendency that forces a rising action on the side toward the inside of the turn. When the car turns and begins to lean over, the sway bar uses the upward force on the outer wheel to lift on the inner wheel, thus keeping the car more level.

Control Arms

A control arm is a bar with a pivot at each end, used to attach suspension members to the chassis.

When coil springs are used in both front and rear suspension, three or four control arms are placed between the rear axle housing and the frame to carry driving and brake torque. The lower control arms pivot on the frame members and sometimes support the rear coil springs to provide for up-and-down movement of the axle and wheel assembly.

A-arms are control arms with two inboard pivots, giving strength. Some front end designs use control arms instead of A-arms, usually to save weight and add adjustability.

Wheel Alignment

Aligning a vehicle's front wheels is the job of balancing the steering angles with the physical forces being exerted. The steering angles are; caster, camber, toe-in, steering axis inclination, and toe-out on turns. The physical forces are gravity, momentum, friction, and centrifugal force. Since so many factors are involved in front wheel alignment, it is also called front end alignment, steering alignment, steering balance, or steering geometry. Alignment is more than just adjusting the angularity of the front wheels. With steadily increasing production of front wheel drive vehicles with independent rear suspension, four wheel alignment is often required. For ideal wheel alignment, certain conditions would have to be met. Both front tires will be the same brand, size, and type. Each will have the same degree of tread wear, and be inflated with the same pressure. Each wheel is properly and equally adjusted for angularity, each tire will maintain the same area of tread contact on a smooth road surface. Obviously, it is impossible to maintain all these requirements. The steering control rods are used to adjust toe-in and toe-out. The upper and/or lower control arms are adjusted to affect the camber angle. Caster is usually not adjustable. With all the weight balance factors to be checked out and corrected, it is obvious that wheel alignment is more than just an adjustment of the steering angles. The whole theory of wheel alignment revolves around balanced weight distribution on the wheels and proper tire tread contact with the road surface while the vehicle is in motion.