The History of Car Steering and Suspension
"Suspension," when discussing cars, refers to the use of front and rear springs to suspend a vehicle's "sprung" weight. The springs used on today's cars and trucks are constructed in a variety of types, shapes, sizes, rates, and capacities. Types include leaf springs, coil springs, air springs, and torsion bars. These are used in sets of four for each vehicle, or they may be paired off in various combinations and are attached by several different mounting techniques. The suspension system also includes shocks and/or struts, and sway bars.
Back in the earliest days of automobile development, when most of the car's weight (including the engine) was on the rear axle, steering was a simple matter of turning a tiller that pivoted the entire front axle. When the engine was moved to the front of the car, complex steering systems had to evolve. The modern automobile has come a long way since the days when "being self-propelled" was enough to satisfy the car owner. Improvements in suspension and steering, increased strength and durability of components, and advances in tire design and construction have made large contributions to riding comfort and to safe driving.
Cadillac allegedly produced the first American car to use a steering wheel instead of a tiller.
Two of the most common steering mechanisms are the "rack and pinion" and the standard (or recirculating-ball) systems, that can be either manual or assisted by power. The rack and pinion was designed for sports cars and requires too much driver muscle at low speeds to be very useful in larger, heavier cars. However, power steering makes a heavy car respond easily to the steering wheel, whether at highway speeds or inching into a narrow parking place, and it is normal equipment for large automobiles.
The suspension system has two basic functions, to keep the car's wheels in firm contact with the road and to provide a comfortable ride for the passengers. A lot of the system's work is done by the springs. Under normal conditions, the springs support the body of the car evenly by compressing and rebounding with every up-and-down movement. This up-and-down movement, however, causes bouncing and swaying after each bump and is very uncomfortable to the passenger. These undesirable effects are reduced by the shock absorbers.
The manual steering system incorporates: 1. steering wheel and column, 2. a manual gearbox and pitman arm or a rack and pinion assembly, 3. linkages; steering knuckles and ball joints; and 4. the wheel spindle assemblies.
In Pittman arm systems, the movement inside the steering box causes the Pitman shaft and arm to rotate, applying leverage to the relay rod, which passes the movement to the tie rods.
Power steering systems add a hydraulic pump; fluid reservoir; hoses; lines; and either a power assist unit mounted on, or integral with, a power steering gear assembly.
There are several different manual steering gears in current use. The "rack and pinion" type is the choice of most manufacturers. The "recirculating ball" type is a past favorite because the balls act as a rolling thread between the wormshaft and the ball nut. Another manual steering gear once popular in imported cars is the "worm and sector" type. Other manual gears are the "worm and tapered pin steering gear" and the "worm and roller steering gear."
The steering wheel and column are a major source of injury to the driver, and a range of energy-absorbing and non-intrusion designs have been developed. There is great variation in these designs, some of which are now thought to be not fully effective.
Energy-absorbing columns have to serve two functions. First, they must stop the steering wheel and column from being pushed to the rear as the front of the car is crushed in an impact. Before such designs were invented, a common feature of driver injury was for the chest to be impaled by the steering column. The energy-absorbing column must also provide the driver with a tolerable impact as he moves forward and strikes the wheel with his chest. At that point in the crash, the column should build up the load on the driver's chest to a tolerable level, and then deform under that load to give a "ride-down" for the driver.
Several design problems are presented in providing this system. One major problem is that collapse of the column due to the frontal crush of the car should not hinder its performance for providing ride-down for the driver's chest. The system must also be so designed that under crash conditions, the wheel stays in such a position that it will strike the driver's chest and not move upwards into the region of his face, or downwards into his abdomen.
The steering linkage is made of interconnected parts which move every time the steering wheel is turned. The rotating movement of the steering column activates mechanisms inside the steering box. Tie rod ends, which join the key parts, pass on the steering wheel's motion no matter what the angle of the linkage or the vibration from the road. In a pitman arm steering setup, the movement inside the steering box causes the Pitman shaft and arm to rotate, applying leverage to the relay rod, which passes the movement to the tie rods. The steering arms pick up the motion from the tie rods and cause the steering knuckles to turn the wheels. The steering linkages need regular maintenance for safe operation, such as lubrication and inspection. Faulty steering links can cause tire wear at the least, and complete loss of control of the vehicle at worst. "Popping" noises (when turning the wheels) usually indicate worn out steering linkages.
Manual Rack and Pinion Steering
A typical rack and pinion steering gear assembly consists of a pinion shaft and bearing assembly, rack gear, gear housing, two tie rod assemblies, an adjuster assembly, dust boots and boot clamps, and grommet mountings and bolts. When the steering wheel is turned, this manual movement is relayed to the steering shaft and shaft joint, and then to the pinion shaft. Since the pinion teeth mesh with the teeth on the rack gear, the rotary motion is changed to transverse movement of the rack gear. The tie rods and tie rod ends then transmit this movement to the steering knuckles and wheels.
Manual Recirculating Ball Steering
With the manual recirculating ball steering gear, turning forces are transmitted through ball bearings from a "worm gear" on the steering shaft to a sector gear on the pitman arm shaft. A ball nut assembly is filled with ball bearings, which "roll" along grooves between the worm teeth and grooves inside the ball nut. When the steering wheel is turned, the worm gear on the end of the steering shaft rotates, and movement of the recirculating balls causes the ball nut to move up and down along the worm. Movement of the ball nut is carried to the sector gear by teeth on the side of the ball nut. The sector gear then moves with the ball nut to rotate the pitman arm shaft and activate the steering linkage. The balls recirculate from one end of the ball nut to the other through ball return guides.
Manual Worm and Sector Steering
The manual worm and sector steering gear assembly uses a steering shaft with a three-turn worm gear supported and straddled by ball bearing assemblies. The worm meshes with a 14-tooth sector attached to the top end of the pitman arm shaft. In operation, a turn of the steering wheel causes the worm gear to rotate the sector and the pitman arm shaft. This movement is transmitted to the pitman arm and throughout the steering train to the wheel spindles.
Worm and Tapered Peg Steering
The manual worm and tapered peg steering gear has a three-turn worm gear at the lower end of the steering shaft supported by ball bearing assemblies. The pitman shaft has a lever end with a tapered peg that rides in the worm grooves. When the movement of the steering wheel revolves the worm gear, it causes the tapered peg to follow the worm gear grooves. Movement of the peg moves the lever on the pitman shaft which in turn moves the pitman arm and the steering linkage.
Manual Worm and Roller Steering
The manual worm and roller steering gear is used by various manufacturers. This steering gear has a three-turn worm gear at the lower end of the steering shaft. Instead of a sector or tapered peg on the pitman arm shaft, the gearbox has a roller assembly (usually with two roller teeth) that engages the worm gear. The assembly is mounted on anti-frictional bearings. When the roller teeth follow the worm, the rotary motion is transmitted to the pitman arm shaft, pitman arm and into the steering linkage.
Over the years, power steering has become a standard equipment item on many automobiles. The demand for this system has caused power steering to be installed on over 90%% of all domestic new car production. All systems require a power steering pump attached to the engine and driven by a belt, a pressure hose assembly, and a return line. Also, a control valve is incorporated somewhere in the hydraulic circuit. "Power steering" is really "power assisted steering." All systems are constructed so that the car can be steered manually when the engine is not running or if any failure occurs in the power source.
Most power steering pumps contain a flow control valve, which limits fluid flow to the power cylinder to about two gallons per minute, and a relief valve which limits pressure according to system demands.
Power Rack and Pinion
Power rack and pinion steering assemblies are hydraulic/ mechanical unit with an integral piston and rack assembly. An internal rotary valve directs power steering fluid flow and controls pressure to reduce steering effort. The rack and pinion is used to steer the car in the event of power steering failure, or if the engine (which drives the pump) stalls.
When the steering wheel is turned, resistance is created by the weight of the car and tire-to-road friction, causing a torsion bar in the rotary valve to deflect. This changes the position of the valve spool and sleeve, thereby directing fluid under pressure to the proper end of the power cylinder. The difference in pressure on either side of the piston (which is attached to the rack) helps move the rack to reduce turning effort. The fluid in the other end of the power cylinder is forced to the control valve and back to the pump reservoir. When the steering effort stops, the control valve is centered by the twisting force of the torsion bar, pressure is equalized on both sides of the piston, and the front wheels return to a straight ahead position.
Integral Power Steering Gears
A representative of an integral power steering gear is used on certain General Motors rear-wheel drive cars and on American Motors four-wheel drive. This power steering gear uses a recirculating ball system in which steel balls act as rolling threads between the steering worm shaft and the rack piston. The key to its operation is a rotary valve that directs power steering fluid under pressure to either side of the rack piston. The rack piston converts hydraulic power to mechanical force. The rack piston moves up inside the gear when the worm shaft turns right. It moves down when the worm shaft turns left. During these actions, the steel balls recirculate within the rack piston, which is power assisted in movement by hydraulic pressure. (See also Manual Recirculating Ball Steering)
Power Steering Hoses
The power steering hoses are used to transmit hydraulic fluid under pressure from the pump to the power cylinder and to return. Besides this, the hoses must provide the proper amount of expansion to absorb any shock surge and offer enough restriction to the fluid flow to keep the pump cavity full of fluid at all times.
Power steering hoses are specially designed rubber hoses with metal fittings at each end which screw together with your power steering system. They contain power steering fluid at high pressures, and allow the system to circulate the fluids between the pump and the power cylinders.
In its most basic form, a wheel alignment consists of adjusting the angles of the wheels so that they are perpendicular to the ground and parallel to each other. The purpose of these adjustments is maximum tire life and a vehicle that tracks straight and true when driving along a straight and level road.
This article begins with information that any motorist should know; however, if you are interested in learning more about this topic, click on the underlined words for more detailed explanations of each term. We will cover various levels of detail with the deepest levels containing information that even a wheel alignment technician will find informative.
If you know anything about wheel alignment, you've probably heard the terms Camber, Caster and Toe-in.
Camber is the angle of the wheel, measured in degrees, when viewed from the front of the vehicle. If the top of the wheel is leaning out from the center of the car, then the camber is positive ,if it's leaning in, then the camber is negative. If the camber is out of adjustment, it will cause tire wear on one side of the tire's tread. If the camber is too far negative, for instance, then the tire will wear on the inside of the tread.
Camber wear pattern
If the camber is different from side to side it can cause a pulling problem. The vehicle will pull to the side with the more positive camber. On many front-wheel-drive vehicles, camber is not adjustable. If the camber is out on these cars, it indicates that something is worn or bent, possibly from an accident and must be repaired or replaced.
When you turn the steering wheel, the front wheels respond by turning on a pivot attached to the suspension system. Caster is the angle of this steering pivot, measured in degrees, when viewed from the side of the vehicle. If the top of the pivot is leaning toward the rear of the car, then the caster is positive, if it is leaning toward the front, it is negative. If the caster is out of adjustment, it can cause problems in straight line tracking. If the caster is different from side to side, the vehicle will pull to the side with the less positive caster. If the caster is equal but too negative, the steering will be light and the vehicle will wander and be difficult to keep in a straight line. If the caster is equal but too positive, the steering will be heavy and the steering wheel may kick when you hit a bump. Caster has little affect on tire wear.
The best way to visualize caster is to picture a shopping cart caster. The pivot of this type of caster, while not at an angle, intersects the ground ahead of the wheel contact patch. When the wheel is behind the pivot at the point where it contacts the ground, it is in positive caster. Picture yourself trying to push the cart and keep the wheel ahead of the pivot. The wheel will continually try to turn from straight ahead. That is what happens when a car has the caster set too far negative. Like camber, on many front-wheel-drive vehicles, caster is not adjustable. If the caster is out on these cars, it indicates that something is worn or bent, possibly from an accident, and must be repaired or replaced.
The toe measurement is the difference in the distance between the front of the tires and the back of the tires. It is measured in fractions of an inch in the US and is usually set close to zero which means that the wheels are parallel with each other. Toe-in means that the fronts of the tires are closer to each other than the rears. Toe-out is just the opposite. An incorrect toe-in will cause rapid tire wear to both tires equally. This type of tire wear is called a saw-tooth wear pattern as shown in this illustration.
If the sharp edges of the tread sections are pointing to the center of the car, then there is too much toe-in. If they are pointed to the outside of the car then there is too much toe-out. Toe is always adjustable on the front wheels and on some cars, is also adjustable for the rear wheels.
Four Wheel Alignments
There are two main types of 4-wheel alignments. In each case, the technician will place an instrument on all four wheels. In the first type the rear toe and tracking is checked, but all adjustments are made at the front wheels. This is done on vehicles that do not have adjustments on the rear. The second type is a full 4-wheel alignment where the adjustments are first made to true up the rear alignment, then the front is adjusted. A full 4-wheel alignment will cost more than the other type because there is more work involved.
Other facts every driver should know about wheel alignments.
A wheel alignment should always start and end with a test drive.
The front end and steering linkage should be checked for wear before performing an alignment.
The tires should all be in good shape with even wear patterns.
Pulling problems are not always related to wheel alignment, problems with tires, brakes and power steering can also be responsible. It is up to a good wheel alignment technician to determine the cause.
Types of Tires
No tire can handle every road condition and driving style perfectly. Positive attributes are always offset by negative factors, as the following list of tire types shows:
All-Season Tires: The Jack-of-all-trades of the tire world, and, as a result, they're the most compromised. They provide only adequate traction and handling, but they have long tread life and a smooth, quiet ride. They're also relatively affordable.
Touring All-Season Tires: These tires combine good handling with a civilized ride. Their performance oriented construction means that they’re somewhat noisier and harsher than regular all-season tires. They're also more expensive than regular all-season radials, but last just as long. Some manufacturer’s arbitrarily add "touring" to a tire’s name as a selling point.
Performance Tires: Wider tread and lower profiles combine good looks with good grip for precise, high-speed driving. Performance tires tend to have a harsh, noisy ride, relatively poor wet traction, bad snow traction, and they wear out faster than all-season radials. They’re also much more expensive. The price of ultra-high performance tires can cause your jaw to drop.
Conventional Snow Tires: Have chunky, aggressive treads that dig down to pavement covered by snow and ice. They’re noisy and handle poorly on dry roads. They're more expensive than all-season radials. They should last a long time, especially since they're only on the car for one season each year. Studded snow tires have tiny metal studs embedded in the tread for even better traction. (These days snow tire use is less common than in past decades. If you live in a place where it snows, and you drive a rear-wheel drive car, invest in a set of snow tires.)
"High-Tech" Snow Tires: Have precision engineered tread patterns and state-of-the-art multi-cell compounds which lend to good ice/snow traction and stopping ability. They can be used all year, but they’re noisy and somewhat clumsy on dry pavement. They're expensive and wear out quickly.
Light Truck Tires: Specifically designed for trucks and sport-utility vehicles, yet they are as diverse as passenger car tires. "Highway ribbed," on-road tires emphasize civilized ride and handling, while aggressive "off-road" or "mudder" tires have a loud, harsh ride and sloppy handling on pavement. Light truck tires are more expensive than passenger car tires due to their larger sizes, higher load ratings and heavy-duty construction. Deep treads mean that they'll last a relatively long time.
There are a variety of specialty tires:
Rain Tires: Have a drainage channel in the tread that directs water away from the tire's surface more efficiently than conventional drainage grooves.
High Flotation Tires: Big, wide tires that people put on 4x4 trucks and sport-utilities so they can drive on the sand without sinking. These tires have poor traction in the ice and snow, so put those skinny, un-cool tires back on the truck for the winter.
Directional Tires: Have a "one-way" tread pattern optimized for the direction the tires rotate on the car.
Asymmetrical Tires: Combine multiple tread patterns in order to make a more well-rounded performance tire.
Self-Sealing Tires: Have a flexible inner-lining that seals around an object if punctured, stopping air loss.
"Twin" Tires: This setup employs two thin, "half-width" tires which are mounted on a special wheel. If one tire goes flat, the other "half" can still support the car.
"Run-flat" Tires: Use special rubber compounds and reinforced sidewalls that can support the car even when deflated -- allowing limited travel.
"Lifetime" Tires: Last for many years, as the name suggests. These tires wear out very slowly while delivering adequate traction.