Saving Your Skin -

Saving Your Skin

Adapted from Larry Carley's article in ImportCar

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’s 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 don’t, and when a tire fails it can have tragic consequences. Even if the failure rate is only one in 100,000 tires, it’s one failure too many for the vehicle owner.

Under Pressure
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.

Since many motorists aren’t tops in the preventive maintenance department, you should make it a habit to always check the inflation pressure in all four tires and the spare when vehicles are in your shop for service. It doesn’t matter what type of repair you’re performing on the vehicle; what matters is taking a few extra minutes to check the tires for your customers.

411 on Tire Inflation
When checking inflation pressure, refer to the inflation chart in the owner’s 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.

Customers should be warned not to judge inflation pressure by appearance alone, especially on today’s 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 the tires need to be checked on a regular basis: At least once or twice a month and before every long trip.

Whoa – That’s Too Much

  • 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.

  • 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 don’t, recommend upgrading to a tire with a higher load rating.

Caution: Hazards Ahead
An exploded truck tire scattered across the highway (also known as alligators) 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. The best advice for your customers is to avoid running over debris on the road, potholes and other such hazards, but sometimes they don’t see them until it’s too late. That’s how many tires are cut, punctured and damaged.

If a puncture doesn’t 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.

Sometimes There’s a Defect
Though not often, 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 doesn’t look right, don’t take a chance – replace it.

If you’re 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 these are usually covered by a prorated tread warranty.

Watch Those Speeds
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 vehicle’s 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’s 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 now factory-equipped with 18-inch, V-rated tires.

Make sure that the speed rating on the tires matches the vehicle requirements and owner’s driving habits. If they don’t, recommend upgrading to a better set of tires.

Installation 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″ rims).

  • If you mount tires, make sure you are trained to use the tire mounting 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 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.

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