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Wheels & Tires
Tire Inspection
 In use, the tires of a vehicle are constantly in danger of being damaged. The tires may run over sharp objects or strike large obstructions, such as curbs or rocks. When the tires are being inspected during any type of service, the mechanic should be alert for all types of cuts, punctures, and bruises.
When inspecting cuts, remove the tire for repair if the cut extends to or through any of the fabric of the plies. When there are small cuts in the tread which do not reach the fabric, the tire need not be removed for repair. A bulge or unusual lump on any part of the tire indicates internal damage to the plies, and the tire should be removed for repair or replacement. The driver will normally remove sharp objects which have entered the rubber of the tire.
On trucks equipped with dual tires in the rear, a visual check should be made to ensure that no large rocks are lodged between the' tires. In addition to damaging the tires, rocks can be thrown for great distances by the fast-turning wheels.
 Drivers are sometimes guilty of driving a truck equipped with dual wheels when one of the tires is flat. With two tires mounted together, a good tire supports a flat tire during operation. However, the good tire is overloaded and is likely to blow out, or the flat tire can slip on the rim and destroy the tube or cause further damage to the tire.
A mechanic can check dual tires by kicking the tires or striking both tires with some object that will not bruise the tires. A flat tire on one of the dual wheels will not bounce from the blow. This method is of no use if a tire has low pressure, but it will show if one is completely flat.
Excess heat will damage tires. When a tire flexes too much due to low pressure, too much heat is generated and the rubber may separate from the fabric.
 On commercial-type treads, the tread gage issued with the organizational tool set may be used to check depth. Normally, the tread should not be less than 1/16 inch.
Some of the causes of rapid tire wear are misaligned wheels, excessive speed, improper loading, grabbing brakes, and improper vehicle operation. A tire will normally wear with a smooth surface, but when forced to slide or drag on the road, the surface becomes rough and scuffed. Operating a vehicle in front-wheel drive more than required can also increase tire wear. During the winter when tire chains are in use, improper installation or use of chains can chew pieces out of the tires. When installed on the wheel, sharp edges of tire chains should face away from the tire.
 If the tire has been driven on too long while not wearing evenly, it may be damaged beyond repair. Once the wear has extended into the fabric of the plies, it is unlikely the tire can be repaired. Uneven wear can be caused by improper air pressure, incorrect steering adjustments, faulty brakes, bad shock absorbers, loose wheel bearings, and poor driving by the operators.
Front tires on a vehicle with too much toe-in will wear the outer edges at a fast rate. If the front tires toe-out when the vehicle is traveling straight ahead, the tires will wear rapidly on the inner edges. Improper toe-in or toe-out forces the tires to slide or drag sideways as they roll over the road surface. A sharp featheredge is left on the edges of the tire treads because of the sliding motion.
Too much free play in the steering linkages, loose wheel mountings, or loose wheel bearings can also cause uneven wear on the front tires. Brake shoes that grab on any of the wheels of a vehicle will cause the tire to slide and wear unevenly.
Any hard-driving practices by the operator, such as moving through turns too fast and stopping and starting too quickly, will cause uneven wear on the tires. Also, it is the responsibility of the vehicle operator to ensure that the tires have the correct tire pressure. If the driver fails in this job, the tires wear unevenly or fail too early.
When a tire is operated with too little air pressure, the center of the tire will buckle inward and the outer edges will carry the load. This causes the outer edges to wear very fast. Also, a tire without enough air pressure will flex more than it should and generate too much heat. If operated with too much tire pressure, the vehicle will ride on the crown or center of the over-expanded tire and, thus, wear the center of the tread too fast.
Differences in the sizes of tires can cause increased wear on the tires and drive trains. Tires of different size on either side of the front of the vehicle can make steering and braking difficult. On any of the driving axles, unequal-size tires on opposite sides of the vehicle will force the differential to work more than necessary. When two unequal-size tires are mounted side by side on rear dual wheels, the tire with the most tread or larger diameter will be forced to carry more of the load. With one tire carrying the load of two, the working tire is much more likely to fail. On vehicles that have more than one driving axle, each axle will be driven at exactly the same speed. If the tires on the different axles have different diameters, some of the tires will be forced to slip to keep the wheel speeds matched, because the larger tire covers more ground during each revolution.
 Often the vehicle driver will be careless with the valve caps because they are not absolutely necessary to keep the vehicle running. The mechanic should check to see if the caps are present each time the tires are inspected, because they can prevent failure of the tires due to leaking valves. When the caps are not present, mud, dirt, or other foreign matter can enter the tire valve openings. This can prevent proper closing of the valve and allow dirt and moisture to be forced into the tire tube as it is inflated with air. Most valve caps contain a seal or gasket that provides a safeguard against a leaky valve. To function properly and to prevent small air leaks, the valve caps must be snug when installed.
The lug nuts that retain the wheels may work loose during the operation of the vehicle. While inspecting, the mechanic should check all lug nuts by trying to tighten them with a wrench. When loose lug nuts are found, the nuts should be tightened to the specifications in the technical manual.
Loose front-wheel bearings, which can cause excess tire wear, can be located by jacking the vehicle up and rocking the wheels back and forth. The free play can be felt at the wheel. This check may also reveal free play in kingpins, steering knuckles, or control arms. The mechanic should first determine exactly where the free play is located. If loose wheel bearings are found, they should be adjusted in accordance with the vehicle technical manual.
 Cracks in the outside rubber of the tire should be carefully inspected. Cracks usually spread out from the center of the tire and may extend all the way around the sidewall of the tire. The cracks are caused by the cord plies below the rubber becoming weak and spreading apart. This forces the rubber to crack open. Failure of the fabric of the tire is usually due to age and/or dry rot. As cracks open in the rubber, water will enter, and the complete failure of the fabric is speeded up. Once the fabric of the tire becomes weak, there is danger of a blowout any time a load is applied. When dry rot is suspected, the tire should be replaced. In all cases where there is doubt as to the service ability of a tire, the mechanic should seek help from the maintenance supervisor.
If the tire was carefully inspected prior to removal from the wheel, only those areas that could not be seen while mounted need to be inspected. If no inspection has been made, make all of the checks listed for a mounted tire. In addition, check the inside surfaces and beads. Check the bead for damage. Bead damage often occurs during installation and removal of the tire from the wheel. It is particularly important to check the outside of the bead on the tubeless tires since this area acts as a seal to retain the air. Check the inner surface of the tire for cuts, punctures, and bulges. If the cord plies have been pulled loose from the normally smooth inner surface, it indicates the tire has been operated while flat. |
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Introduction
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 Articles
When Parts Go Bad
Glossary
Article Pages
1. An Introduction to Wheels and Tires
2. Tires
3. Learning To Read Your Tires
4. Manipulating The System
5. Valves
6. Tire Pressure Monitoring Systems (TPMS)
8. Tire Wear Guide
9. Tire Rotation
10. Wheel Assembly
11. Wheel And Rim Construction
Hot Topics
-> 4 Things You Can Start Doing Today To Extend The Life Of Your Tires
-> New Tires Guide
-> Tire Safety Tips
-> What Does It Mean When My Wheels Are Imbalanced?
-> Wheel Balancing
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