The tires are where the rubber meets the road as far as traction, steering, braking and driving safety are concerned. The type of tires that are on a vehicle can make a huge difference in how well it rides and handles, how it hugs the pavement in both wet and dry weather, and how satisfied the owner is with his car or truck. All things considered, tires are pretty darn important.
It is amazing that tires hold up as well as they do, considering their vulnerability to road hazards. Many tires today are easily capable of going 60,000 to 80,000 miles or more provided they are properly installed, maintained and aligned, and regularly inspected. With good care and "normal" use, most tires will go the distance without a problem. But sometimes they do not, and when a tire fails it can have tragic consequences. Even if the failure rate is only one in 100,000 tires, it is one failure too many for the vehicle owner.
TIRE PRESSURE CHECKS
One of the most common causes of tire failure is underinflation. Tires that are underinflated experience excessive flexing in the sidewalls that causes them to run dangerously hot, especially at highway speeds during hot weather. The buildup of heat can lead to tread separation or a sudden blowout. The underlying cause here is often lack of maintenance (not checking the inflation pressure of the tires regularly) or a slow leak that has allowed the tire to lose air. Punctures, rim leaks and leaky valves can all cause a tire to lose air.
The main responsibility for preventing this type of failure falls squarely on the shoulders of the vehicle owner. Motorists should read their owners manual, or the tire inflation decal in the door jam or glove box, and know how much pressure their tires require. They should own a tire pressure gauge and know how to use it. They should check inflation pressures when the tires are cold and add air as needed to maintain the recommended pressure. If a tire is losing air, they should take their vehicle to a tire dealer or repair shop so the problem can be diagnosed and fixed.
Since many motorists do not do any of these things, technicians should make it a habit to always check the inflation pressure in all four tires and the spare when vehicles are in the shop for service. It doesn't matter what type of repair work is being done; what matters is taking a few extra minutes to check the tires.
According to a recent survey by the Car Care Council, 54 percent of vehicles (that’s more than half!) inspected during National Car Care Month were found to have improperly inflated tires. Another 14 percent were also found to have worn-out tires that needed to be replaced.
When checking inflation pressure, refer to the inflation chart in the owners manual or the decal in the glovebox or door jam for the recommended inflation pressures. Don't guess because you might guess wrong. Also remember that the recommended pressure will vary according to vehicle load and speed. Heavier loads and sustained high-speed driving usually require a few extra pounds of pressure. Remember, proper inflation pressure is essential for maximum tire life, good handling, traction, braking, fuel economy and driving safety.
Also, don't try to judge inflation pressure by appearance alone, especially on low-profile performance tires. A low tire may not look low at all. In fact, many tires don't look low until they are dangerously underinflated. That's why tires need to be checked on a regular basis: At least once or twice a month and before every long trip.
TOO MUCH AIR: OVERINFLATED TIRES
Overinflating tires can be just as bad as underinflation because it increases ride harshness and makes the tire more vulnerable to damage caused by potholes and curbs. Overinflation typically occurs when somebody adds air to a tire until it "looks full." Or, they don't use an accurate tire gauge when filling the tire. Never exceed the maximum pressure rating on the side of the tire. Always follow the OEM-recommended inflation pressure for vehicle load and operating conditions.
DON'T OVERLOAD TIRES
Overloading a vehicle or driving on tires that do not meet the load rating requirements for the application is asking for trouble. This is more of an issue with pickup trucks, vans and SUVs than it is with passenger cars, especially those that may be used as utility vehicles to haul building materials or other unusually heavy loads. The best way to prevent this kind of failure is to check the load rating of the tires and make sure that they match the application. If they do not, the tires should be upgraded to ones with a higher load rating.
ROAD HAZARDS TO TIRES
An exploded truck tire scattered across the highway may not look dangerous, so many people will drive over the debris. But tire remnants often contain sharp pieces of steel wire that can puncture tires. Avoid running over debris on the road, potholes and other such hazards. Sometimes you don't see the debris until it is too late. That's how many tires are cut, punctured and damaged.
If a puncture does not cause a tire to immediately go flat, it may weaken the tire and cause it to fail later or under high speed/load/temperature conditions. Ultra low-profile tires are especially vulnerable to sidewall damage when hitting curbs or potholes because of the narrow distance between the tread and rim.
When inspecting low-profile tires, pay close attention to the sidewalls as well as the tread for signs of damage. If a tire has gone flat or is losing air, it should be removed from the rim and carefully inspected inside for damage. Don't just plug it and let it go because the tire may have hidden damage that can't be detected from the outside.
FACTORY TIRE DEFECTS
Here's a subject no tire manufacturer likes to talk about because of obvious liability issues. But manufacturing defects do occur that may result in poor adhesion between the tread and belts - which may result in tread separation or a blowout. Fortunately, factory defects are rare and are almost always covered under warranty.
Brand new tires should always be inspected for obvious defects such as bulges, cracks or lumps after they are mounted on rims and inflated for the first time. If something does not look right, don't take a chance - replace it.
If you are inspecting a set of used tires on a vehicle and find a tire that has bulges, blisters, missing chunks of rubber, cracks that indicate tread separation, etc., these are dangerous structural defects. The tire should be replaced immediately - and it should be covered by a prorated tread warranty.
When repairing tires, most experts recommend using a plug or combination path/plug that fills the hole. A patch alone that does not fill the hole and may allow moisture to penetrate the tread and reach the steel belts. This can lead to rusting and increase the risk of tread separation and tire failure later on.
TIRE SPEED RATINGS & DRIVING TOO FAST
Driving at sustained high speeds on tires that are not speed rated or are badly worn is just plain stupid, especially during hot weather or with an overloaded vehicle. Speed-rated tires have additional reinforcements and are better able to dissipate heat than ordinary tires and should always be used for these types of applications.
Some newer vehicles have a built-in speed limiter that is matched to the OEM tires. For example, if the factory tires are H-rated with a maximum sustained speed of 130 mph, the engine computer may not allow the vehicle to be driven any faster than the rated speed. But with vehicles that do not have this feature, there is nothing to keep the driver from pushing the tires beyond their maximum speed rating. For high-performance cars, a "V" (up to 149 mph) or "Z"-rated (149 mph-plus) tire may be required. Even cars like the 2004 Nissan Maxima are factory-equipped with 18-inch, V-rated tires.
CAUTION: It is possible to use a special "tuner" scan tool to disable the speed limiter setting in the engine computer so a vehicle can be driven faster. The danger here is that the vehicle may be capable of going faster than the speed rating of the original tires. This may increase the risk of a high speed tire failure unless the tires are replaced with ones that have a higher speed rating.
Make sure that the speed rating on the tires matches the vehicle requirements. Better to have over rated tires than under rated tires. If the tires do not have the proper speed rating, they should be replaced with ones that do.
TIRE MOUNTING TIPS
Tires can be damaged if they are not properly mounted. Not using a bead lubricant when mounting a tire on a rim, and stretching or tearing the bead because the tire was not correctly positioned on the rim or in the rim drop center, can cause bead damage that may allow a tire to leak air or suffer a bead failure later on. Overinflating a tire in an attempt to seat it or failing to fully seat the tire can also lead to problems when the tire is returned for service. We've even heard of instances where people have tried to mount a tire on the wrong-sized rim (watch out for 16.5- and 15.5-inch rims).
If you are mounting tires with a tire changer machine, make sure you know how to use the equipment. Some low-profile tires can be tricky to mount and dismount. Asymmetric rims, centerless rims and three-piece cylindrical rims with no drop center can also be a challenge for outdated tire changing equipment. BMW Z3 cars, for example, have wheels with a reverse drop center and AH2 bead locks that require a special dismounting and mounting procedure. According to one tire changer manufacturer, the best way to handle AH2 bead lock rims is to break the bead by rolling off the rim, rather than forcing it off with a shovel-style bead breaker.
The same precautions go for wheels that have built-in tire pressure monitoring systems. Care must be used when breaking the bead and dismounting and mounting the tire on the rim so that the pressure monitor isn’t damaged. Run-flat tires with liners may also require special installation procedures.
Safety beads and closer bead-to-rim clearances on many alloy wheels also mean it takes more air pressure to seat the beads. The old rule of using no more than 40 psi to seat a bead may not always apply on some wheels. For this reason, an inflation cage should be used if 60 to 80 psi is required to seat a bead. Inflation cages should always be used for high-pressure truck tires.
Ultra low-profile tires can also be easily damaged if the sidewall is deflected too far when dismounting or mounting a tire on a rim. Using a shovel-style bead breaker can be risky because if the bead breaker is placed too high on the sidewall when dismounting the tire, it may damage the tire. For these types of tires, a tulip/rim-style tire changer that uses a pair of rollers to push the bead loose works best.
The bead breaker on a tulip/rim-style tire changer applies no force to the wheel itself, only the tire, so there is much less risk of damaging either the rim or tire. These machines also use a clamping system that grasps and holds the wheel from the inside out (or the outside in depending on the application), which eliminates the center post and cone. This allows you to handle centerless rims.
TIRE BALANCE
A balancer is an esential piece of equipment for tire service. A balancer is needed to balance new tires, to rebalancing tires that have been repaired, remounted or run more than 25,000 miles since their last balance, and to solve vibration problems.
Only 1/4-ounce of imbalance can produce a noticeable vibration, so it is important to have a balancer that is both accurate and easy to use. Many electronic off-car spin balancers today are capable of balancing wheels to within a few hundredths of an ounce.
Most balancers operate at low speeds. This helps extend motor life and reduces cycle times as well as risk to the operator. Older balancers typically had to spin a wheel at about 500 rpm (55 to 60 mph) to generate a usable signal. But the more sensitive electronics in today's computerized balancers can detect vibrations at 100 rpm (10 to 15 mph). Some units also have the added capability to detect excessive tire runout and radial force variations in the sidewall that can cause vibrations.
WHEEL ALIGNMENT
Uneven or unusual tire wear often means the wheels are out of alignment and/or the steering or suspension has worn or damaged parts. If you suspect an alignment problem, all four wheels should be checked on an alignment machine to see if they are within factory specifications. Accurate alignment is absolutely essential for maximum tire life, steering stability and good handling.
Ideally, most vehicles should have zero toe and neutral (zero) camber while being driven down the road. Zero toe will minimize tire scrub for maximum tread life, and zero camber will keep the tires rolling straight while distributing the load across the full face of the tread. Achieving these ideal settings when a vehicle is in motion requires static alignment settings that are within the vehicle manufacturer specifications. These specifications are determined by normal vehicle loading (usually the driver only), suspension compliance and design of the vehicle’s steering, suspension and drivetrain.
Periodically checking alignment is the only way to know for sure if the wheels are still within specifications. Alignment should not change once it has been set, but worn or damaged parts, or weak, sagging springs can upset the angles. That’s why many shops recommend an annual alignment inspection as preventive maintenance.
Realigning the wheels may also be required after steering or suspension components have been replaced. Parts such as tie rods, tie rod ends, tie rod sleeves and steering racks obviously require adjustment after installation. But an alignment check and adjustments may also be needed after changing parts such as struts, control arms, bushings, idler arms, center links, etc., because of variances in manufacturing tolerances.
More Tire Articles:
Click Here to See More Carley Automotive Technical Articles
Have A Tire or Alignment Problem? Need Help Now? 