Tire Maintenance

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Oh my, tires!

Do you ever wonder about your tires? Let me explain how they work.

The components of the tires consist of:

  • Tread
  • Sidewalls
  • Beads
  • Wheels
  • Belts
  • Reinforcing cords
  • Tire Pressure
  • What the letters mean
  • Wear Indicators
  • Spare tires

Tires are fabric, steel and rubber devices that, when attached to the WHEELS of a vehicle, provide the contact between the vehicle and the surface over which it travels. Each modern automotive tire supports approximately 50 times its own weight. Compressed air within the tire carries 90 percent of the load, with the tire’s complex structure of fabric steel and rubber carrying the remaining 10 percent.

Many refinements have been made to tires over the years. Refinements in construction, tire geometry and materials have improved the durability and effectiveness of modern tires.

The TREAD is the most important aspect of the tire. It grips the road, and supports the SIDEWALLS, Tread patterns are very important for determining just the right tire for your driving circumstances. For instance, if you are driving on wet surfaces, it is beneficial to choose a tire that has a tread pattern that wipes away water from the small contact patch at the bottom of the tire. Continuous channels that direct the water from the center to the outside of the tire provide the best wet weather grip. For dry surfaces, a tire with a no tread at all will produce the best handling characteristics. However, since tires are subject to different surfaces and temperatures, a good tread pattern provides durability and handling that is adequate for normal driving.

A tire sidewall has two purposes: They flex up and down, cushioning the vehicle from road irregularities and they transfer loads of steering, braking and acceleration. Where the sidewall meets the wheel, the BEADS (hoops of steel covered by rubber) reinforce the area where the tire and wheel meet. The diameter of the bead fixes the tire’s size.

The wheel is a metallic cylinder used to attach the tires to the suspension. Wheels are often chosen for cosmetic purposes, however, looks are not the primary factor in choosing wheels. The wheel is a major component of the suspension. A wheel that is too small will interfere with the operation of the brakes. A wheel that is too big will interfere with the steering operation. A wheel that is too wide causes the tire to wear out prematurely and also causes stress on the other suspension components by moving the center of balance of the suspension out further than it should be. An out of balance condition of the suspension will cause the vehicle to be very unstable in turns.

REINFORCING CORDS are arranged beneath the surface of the tire in a crisscross pattern and give the tire its strength. The classes of tires are determined by the direction of the cords. A bias ply tire has cords positioned between plies or layers of the tire in a crisscross pattern. The bias belted tire has two or more plies of reinforcing cord. A radial tire has cords that are running in a hoop fashion from bead to bead. The radial tire has reinforcing plys running only on the tread area of the tire, while lack of bias sidewall reinforcement makes the radial tire more flexible. This characteristic gives the tire a better grip and longer life. It also gives the radial tire an under-inflated look.

Tires come in a variety of sizes, each designated by a coded sequence. For instance, a tire with the designation: P195/60R14 means that this radial tire is made for a Passenger car, it is 195MM (about 7 1/2 inches) wide, with a 60 percent profile (The height of the tire is 60 percent of the width) for a 14 inch wheel. Tires of different size or types should not be mixed on one car because of differing handling characteristics of different tires. Tire pressure should be maintained at the pressure recommended ON THE TIRE. Radial tires should be rotated regularly front to back only, keeping tires on the same side.

The temperature resistance of a tire and the traction index of stopping ability and traction is rated on the tire by the letters “A” as the highest grade and “C” as the lowest. The higher the speed, the harder the driving, the heavier the load, the hotter the tires run.

The tread wear index is a rating of how well the tire wears. A tire graded “420” should last about 4.2 times as long as a tire rated at “100”. Driving conditions and style affect tread wear differently.

There are a series of letters and numbers on the tire indicating when the tire was manufactured. These numbers are usually on the inside edge of the tire near the rim. The last in the series of numbers is usually a 4 digit number designating week and month of manufacture: 1107 means that the tire was manufactured in the eleventh week of 2007. This tire is good; 4402 means the tire was manufactured in the 44th week of 2002. This tire should be replaced. The life of a tire is about 6 to 7 years. When buying new tires, it would be beneficial to check these numbers on each tire, to assure tires are not too old to use on your car. Old tires tend to begin to deteriorate after 6 years, even of they were never mounted.

TIRE PRESSURE is probably the most important aspect of tire longevity. A tire can lose up to half its pressure and not appear flat. Low tire pressure is the leading cause of tire failure. A properly inflated tire wears longer by staying cooler, the suspension works better, the car handles better and you can get better mileage with properly inflated tires. Tire pressure recommendations are printed on each tires sidewall. Check the tires for the proper pressure, including the important spare tire. Proper rotation helps tires wear evenly. Consult the owners manual for the proper rotation procedure. Alignment is also important for maximum tire wear. Wheels that are aligned properly will extend the life of a tire considerably.

Checking the wear pattern on a tire tells a lot about how the tire is wearing. For instance…if you see that the tire is wearing on the outside and inside, this means that the tire is under inflated. If the tire is wearing in the middle only, the tire has too much pressure. Check the tire recommended pressure, adjust accordingly and maintain that pressure. If the tire is wearing on the inside or the outside edges of the tire, the tires are out of alignment. Alignments should be done on all four wheels at the same time. Never have an alignment done on only the front wheels, as this will cause the rear tires to wear adversely. All tires come with WEAR INDICATORS to tell when the tire should be replaced. If you see a solid bar running across the width of the tire, it is time to replace that tire.

SPARE TIRES can be just as important as the tires on the ground. The best spare tire is the same type of tire as on the car, however, most cars now come with a “space saver” tire. This tire is constructed with similar components but is much lighter and not as durable as a regular tire. The inflation pressure is usually more than a standard tire because of its smaller size. Pressure in the spare tire should be checked at least once a year to make sure that the spare tire is always available when needed in an emergency.

Never exceed the maximum load of your tires. Consult the sidewall of the tire for the maximum load allowable and multiply by four. Your vehicle should never exceed this weight.

Recently, there has been a trend of tire installers to fill new tires with nitrogen. Nitrogen is part of the air we breathe. In fact it is 70% of the air we breathe. It is true that racecar teams use nitrogen in racecar tires. They use it NOT because it is more stable or better. They use it because using a pressurized tank regulated to 100 to 200 PSI is a lot easier than carrying around a big heavy compressor assembly that needs to run all the time. Besides,  Nitrogen is cheaper than compressed air because it’s just one chemical element, instead of two. Nitrogen in car tires is just a waste of money, because the tire installers usually charge anywhere from $5 to $35 per tire. Save your money, don’t use nitrogen in your car tires.

To change a tire in an emergency, you should be sure to park where it is safe and level. If not, keep driving slowly on the flat tire until you come to a place that is safe. Turn on the emergency flashers and set the hand brake with the car in park or 1st gear. Remove the spare tire and the jack from the storage compartment. Position the jack in the place indicated on the jack and start to lift the car. With the wrench positioned horizontally on the lug, use your foot to loosen the lugs counter-clockwise. Raise the car until the wheel is clear of the ground then remove the lugs. Replace the defective tire with the spare tire and install the lugs. Lower the car until the tire touches the ground and tighten the lugs with your foot, clockwise. At your earliest convenience, repair or replace the defective tire and return the fully inflated spare tire to the storage compartment for later use.

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