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Getting the Most Mileage Out of Your Tires Tom T  |
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What can you do to get the most life out of the black, round, rubber hoops we call tires (and insure that your tires are safe)? Today, the average tire costs about $100. And this figure doesn't take into account the cost of the plus-sized stuff like the 22-inch "Dubs" or the special performance rated tires. Tire life depends on the good condition and proper operation of the suspension and steering systems, as well as accurate alignment. All of these elements work together.
Your vehicle's suspension system consists of the components upon which the vehicle's mass rides. It includes shock absorbers and/or struts, springs (coil or leaf) or torsion bars, sway bars, ball joints, control arms. These parts work together to provide a smooth comfortable ride, as well as good control and handling of the vehicle. They take quite a beating on a daily basis and thus wear out, causing the alignment angles to go out of adjustment, and resulting in tire wear and poor handling.
Understanding the relationship between the parts of a suspension may help to increase our awareness of the importance of maintaining our vehicles. For instance, when a shock or strut goes bad, spring oscillation is not dampened. The excessive motion causes accelerated wear on the other suspension parts, such as the ball joints and control arm bushings. In addition, as the tires roll at highway speeds they will bounce, which causes a choppy tire wear called a "scallop pattern." The overall result? Lots of tire noise and short tread life (and even more importantly, poor control and handling that can result in an accident). So it's vital that you keep your car's suspension system in good shape for safer driving and longer tire life.
We all know that if a car is 'out of alignment' the tires wear much faster. To understand this relationship, we've got to take a look at the steering system. To accurately discuss steering, you need to know that there are two types of steering systems, Conventional and Rack & Pinion. Vehicles equipped with Conventional Steering use a steering linkage system. It consists of a series of steel bars that are connected together using ball and socket joints; the system includes such parts as the Pitman Arm, Tie Rods, Drag Link, and Idler Arm. When all bolted together, supported to the frame, and connected to the steering gear box via the Pitman Arm, the car's wheels are able to turn right or left in response to the turning of the steering wheel. There is more room for failure in Conventional Steering because of the numerous ball and socket joints, as well as pivot joints that are affected by road jostle. Add to this package the fact that all of these components are connected, and you can see how they would affect one another as they wear, increasing the rate of wear on the entire system.
The second steering system, Rack & Pinion Steering, allows for more responsive handling and is used predominately in newer cars. It consists of a steering shaft that is controlled (or turned) by the steering wheel. The steering gear is a self-contained system that consists of a small gear called the pinion gear, which meshes with a toothed bar called the rack. The rack is connected to the steering linkage (tie rods) at each end, which control the two front wheels. When the steering wheel is turned right or left, the rack is moved, resulting in the steering of the vehicle. The Rack and Pinion system has fewer moving parts than the conventional system, thus it doesn't wear out as fast and requires less maintenance (fewer alignments).
Finally, when it comes to tire life and safety, alignment is extremely important. Let's take a look at the different alignment angles, and what causes the alignment to go out, and how this affects your car's tires
The term CAMBER refers to the angle of wheel alignment that measures the tilting in or out in reference to the top of the tire. For instance, if a car's camber angle on a tire is too positive than the top of the tire is tilting outward, resulting in excessive wear on the outside rib of the tire tread. If the camber angle is too negative than the top of the tire is tilting inward and the tire will wear on the inmost rib of tread. This angle can be adjusted either by mechanical adjustment or by the addition or removal of shims. Conditions that cause excessive camber are worn ball joints, control arm bushings, strut bearings/mounts, or excessively worn wheel bearings. These parts must be 'tight' (not 'sloppy') to insure an accurate alignment of the camber angle.
The terms TOE IN and TOE OUT: The best way to explain how this angle affects wheel alignment is to look down at the tops of your feet. Imagine that you're hovering above the hood of your car and you can see through the body of the vehicle. Your feet represent the tops of the tires. Now slowly turn your feet inward to an excessive degree. That's what your tires look like when they're toed-in too far. Now turn your feet outward excessively. That's what your tires look like when they're toed-out too far. This alignment angle is adjusted through the lengthening or shortening of a steering linkage part called a tierod (found in both Conventional and Rack & Pinion Steering systems). Obviously when this angle is out or in too far, tires wear out quickly!
As you can see, alignment angles go out as the steering/suspension components wear out. And bad angles means worn tires, which costs you money. Even more importantly, running your car on bad tires means poor handling and could result in an accident. Worn tires can also blow out while driving, which could result in a serious crash. The best way to insure healthy tires and maximum tire life is to have the alignment and steering/suspension checked every 12 months or 12,000 miles. That's cheap insurance!
'Til next time...Keep Rollin'
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 With over 27 years in the automotive industry and nearly a decade in automotive talk radio, Tom Torbjornsen makes learning about cars easy with his personal manner, his expert advice, and his high energy and entertaining style. Tom has the unique gift of simplifying the complex and tearing down the technical, meeting you at your level of understanding. You will be encouraged as you gain the confidence to deal with problems related to the second most expensive purchase you will make in a lifetime your automobile.
Email Tom
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