Suspension and Steering System
Most of the roads that we drive on are not perfectly smooth and straight. S-curves, potholes, speed bumps, construction zones, and weather conditions make it necessary for vehicles to have control mechanisms. A properly working suspension and steering system gives the operator and passengers of the vehicle a smooth and pleasant ride. Shocks, struts, springs, and tires all assist in controlling the automobile by keeping the tires in contact with the road. This section presents the functions and components of suspension and steering systems.

Purpose of the Suspension System
The suspension system helps to control the up and down movement of the vehicle. During braking or going over bumps the suspension system helps provide stability, safety, and control of the vehicle.

Suspension System Components
The suspension components consist of many parts, all of which are attached to and become a part of the chassis. The chassis consists of some or all of the following components:

• Frame or Unibody
  
• Shocks
  
• Springs
  
• Struts
  

Frame or Unibody
The vehicle must have a foundation upon which to build the rest of the vehicle. Some vehicles have a ladder type steel frame that runs the length of the vehicle. Others have partial frames, called unibodies, that connect the body and frame into one unit.

Shocks
The shocks on a vehicle reduce the up and down motion that is produced from going over bumps on the highway. One end of the shock absorber is connected to a stationary part on the frame or unibody, while the other is connected to a suspension component that moves. The shock absorber contains a gas, fluid, and/or compressed air to reduce the number of oscillations (up and down motions) that are produced from driving on uneven roads. Oil leakage around the shock is a sign of it needing replacement.

Springs
Springs work in conjunction with the shocks to help absorb the irregularities in the road surface. Springs come in coil and semi-elliptical shapes. Coil springs are common on the front and rear of a number of vehicles. Semi-elliptical springs, usually called leaf springs, are common on the rear of trucks.

Struts
Struts have become popular on a number of vehicles. Struts basically eliminate the need for shocks and springs on the front and/or rear of a vehicle. They do this by combining the shock and spring into one unit. Struts reduce the weight and space that a comparable spring and shock would use. It should be noted that some vehicles have struts in the front and shocks and springs in the rear while others have struts at each wheel.

Purpose of the Steering System
The steering system controls the directional movements of the vehicle. The steering system, in conjunction with the suspension system, provides control and stability of the vehicle. The motion the operator makes at the steering wheel is transferred to the front wheels.

Steering System Components
Some of the steering system components are connected to the frame of the vehicle while others need to move with the suspension. The following are some of the basic components of the steering system:

• Steering Wheel
  
• Steering Linkage
  
• Power Steering Pump
  

Steering Wheel
The steering wheel is how the operator controls the direction of a vehicle. Slight movements of the steering wheel can easily turn a 2000+ pound vehicle. The steering wheel is connected to the wheels by steering linkage.

Steering Linkage
Steering linkage connects the steering shaft from the steering wheel to the arms that control the wheels on the highway. Steering linkage can include tie rods and tie rod ends, steering knuckles, idler arms, center links, adjusting sleeves, and pitman arms. Many newer vehicles now incorporate a rack and pinion system that works in conjunction with a strut type suspension system to reduce space and weight. The rack, a flat piece with teeth, is connected to the tie rods. The pinion is connected to the steering shaft from the steering wheel. As the operator turns the steering wheel, the pinion turns, moving the rack in the desired direction.

Power Steering Pump
To reduce the amount of effort that a driver needs to exert when steering, a power steering pump is commonly used. The pump, which is driven by a belt on the engine, provides fluid pressure to ease the turning force required by the operator to turn the steering wheel. It is necessary to periodically check the power steering pump reservoir fluid level.

Tires
The tires on a vehicle provide the connection to the road surface. The tires are part of both the steering and suspension system. They are a critical component to driving safely. Tires provide the needed traction (friction) to make driving safe during acceleration, cornering, and braking. The design of tire tread, the part of the tire that comes in contact with the road, determines how well a tire will act on different road conditions, such as ice, water, mud, and snow. A tire with very little tread is more likely to hydroplane. A tire hydroplanes when it is riding on a thin film of water. A tire with tread less than 1/16th of an inch is worn out. Tire wear indicator bars, set at 1/16th of an inch, run perpendicular to the tread to indicate when there is a need for new tires. Tires are designed to give passengers a comfortable ride and the needed traction to control the vehicle. Correct tire pressure is critical to tire wear and handling of the vehicle. Rotating tires and aligning wheels extend tire life. There is more about checking tire pressure and completing tire rotations in the activities on the attached CD. When replacing tires on a vehicle, several things should be considered:

• Tire Plies
  
• Tire Sizes
  
• Tire Grading
  
• Load Ratings
  

Tire Plies
Steel belted all-season radial tires are the most common type of tire. They consist of steel wires running around the tire. Radial ply cords run from the bead (where the tire attaches to the wheel rim) on one side to the bead on the other side. In addition to this, there are other belts directly under the tread for added stability.

Tire Sizes
Tires come in a variety of sizes depending on vehicle size and weight. It is important to replace the tires on the vehicle with the size recommended by the manufacturer. Having tires too big or too small will influence how a vehicle handles. Most tires today are sized in the metric system. The following is an example tire size: P205/70SR14. The first letter can start with a P, C, LT, or T. P stands for passenger, C stands for commercial, LT stands for light truck, and T stands for temporary. Most cars will have passenger tires. Light trucks can come with either passenger or light truck type tires. The 205 stands for the tire width in millimeters. The 70 stands for the aspect ratio or profile of the tire. It compares the cross-sectional height to the cross-sectional width. A lower number will result in an overall lower, wider tire. The letter S may or may not be present on all tires. This indicates that the tire has been tested at speeds at or above 112 mph. Other speed rated letters are H (130 mph), V (149 mph), and Z (+149 mph) – each being tested at the corresponding speeds. The next letter R identifies that the tire is a radial type tire. The last number represents the rim diameter in inches. Common rim sizes are 13, 14, 15, 16, and 17-inch.

Tire Grading
All passenger (P) vehicle tires will have UTQG (uniform tire quality grading) ratings that have been established by the United States Department of Transportation (DOT). These have been established to help the consumer compare tire brands and types. The three UTQG ratings are treadwear, traction, and temperature. The treadwear rating, given as a number, is based on the wear rate of the tire when tested in a controlled setting. For example, a tire graded 300 will last twice as long as a 150 tire. Traction ratings, shown as AA, A, B, or C, represent a tire’s ability to grip the road on a wet surface. An AA rating has superb traction, an A rating has excellent traction, a B rating has good traction, and a C rated tire has poor traction. The third rating, temperature, represents a tire's ability to resist high-temperatures. These are rated as being A, B, or C – where A can withstand the highest temperature.

Load Ratings
Tires are also classified by the amount of load (weight) that they can carry. Most passenger car tires are rated as either standard or extra load. Light truck tires have 4-ply (B load range), 6-ply (C load range), 8-ply (D load range), 10-ply (E load range), or a 12-ply rating (F load range). The load range, ply rating, and maximum inflation pressure are all related. The more plies a tire has, the more load it can carry.

Tire Wear Problems
Inspecting your tires on a regular basis will help you identify how they are wearing. Many things can cause abnormal tire wear: underinflation, overinflation, worn steering components, worn suspension components, tires out of balance, and tire misalignment.

Summary
The suspension system absorbs the bumps in the road to give you a smooth ride. The steering system allows the operator to control the left and right motions of the vehicle. Tires provide the traction (friction) necessary to maneuver the vehicle. Knowing tire specifications can be beneficial when making decisions about new tires. Uniform tire quality grading ratings make it easier for you to compare different tires. Abnormal tire wear patterns can show possible problems with the vehicle. Suspension and steering components work in conjunction with one another to provide a safe ride.

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