The Future of Tire Technology

The biggest change in tire technology is actually a return to the past. Early tires were solid rings of rubber that wrapped around wagon wheels. These tires were hard riding, but also impervious to punctures and very durable -- ideally suited to the rough terrain of the day. Today, tire manufacturers are trying to make the flat tire a distant memory.

Today's run flat tires contain air and are much more complicated in construction than early rubber rings. But, they operate on the same principle: They are tough enough to run without air if necessary.

The above diagram shows the difference in construction between a conventional tire and a stiff-sidewall run-flat tire. In a stiff-sidewall run-flat tire, there is extra sidewall reinforcing rubber that prevents the sidewall of the tire from deflecting. In a inner-liner run-flat, the sidewall is no stiffer than a conventional tire, but a hard rubber or plastic ring inside the tire helps keep the tire's sidewall from deflecting.

There are two different styles of run-flat tires. The first uses very stiff sidewalls that can support the weight of the vehicle in the event of pressure loss. Several tire companies offer this type of run-flat, and they can typically be driven with no air pressure for about 50 miles at speeds up to 55 mph. However, most cannot be repaired after being punctured.

The sidewalls can't be very tall, so most are low-profile designs. Because of this, they are typically used on sports cars such as the Dodge Viper, though they're also available for regular passenger cars and even minivans.

Photo courtesy Michelin Michelin's PAX system is a tire/wheel package that consists of four components: a tire, a wheel, an inner support ring, and a tire-inflation monitor.

The second style is a new design invented by Michelin dubbed the PAX system. It is currently offered in the United States on Rolls Royces and the 2005 Honda Odyssey minivan, but is expected to be available for other applications in the future.

The PAX system isn't just a tire. It's a tire/wheel package that consists of four components: a tire, a wheel, an inner support ring, and a tire-inflation monitor. If the PAX system tire loses air pressure it only drops about halfway down. At that point, the underside of the tread rests on an inner support ring that runs around the circumference of the wheel. According to Michelin, the vehicle can be driven for 125 miles at up to 55 mph.

The PAX system also incorporates a special bead -- the connection between tire and wheel -- that helps lock the tire onto the wheel even if the tire loses air pressure, something traditional run-flat tires -- and regular tires -- don't usually have. Unlike most run-flat tires, the PAX-system tire can be repaired if the hole is in the tread area and less than 1/4-inch in diameter -- as is the case for regular tires.

Because the sidewalls of an un-inflated PAX tire don't support the weight of the vehicle in the event of pressure loss, the sidewalls can be taller than on run-flat tires. They also don't need to be as stiff, which means that the ride quality is better. This makes the PAX system better suited to SUVs, as well as regular passenger cars and minivans.

There's often little change in driving feel to warn the driver the tire has lost pressure, because the tires don't go "flat." Therefore, run-flat tires must be used with a tire-pressure monitoring system, which illuminates a light on the instrument panel to inform the driver of pressure loss.

In lieu of hard-riding or expensive run flat tires, manufacturers are turning to a less-costly but space saving alternative to spare tires: temporary mobility kits (TMK). Also referred to as "fix-a-flat," TMKs consist of an aerosol can containing compressed air and a liquid rubber. The can is connected to the valve stem of the tire, and the air and rubber are injected. The rubber seals the puncture and the air refills the tire.

In theory, the motorist can then drive to the nearest gas station to get the tire repaired. There are several problems with TMKs, though. First, the tire must have a small puncture and still be roadworthy. In many cases, flat tires are destroyed because drivers travel too far while they are under-inflated. This renders the TMK useless. Second, if the TMK is utilized, it often renders a good tire (with a small hole) irreparable. The liquid rubber in the TMKs can also damage expensive wheels and end up being even more expensive for the driver.

Another trend in the industry is light-truck tires with heavy-duty load ratings and passenger-car-tire comfort levels. In the past, pickup truck drivers had to choose between passenger-car tires (which are soft-riding but can't handle heavy-duty loads) or hard-riding, noisy truck tires. OEM and aftermarket tire suppliers have begun to meld the positive characteristics of passenger-car tires with the load capabilities of truck tires. In most cases these new truck tires cost more than conventional passenger-car tires, but that added expense can be well worth it or consumers asking their truck or SUV to do double duty.

Consumers rarely give tires a second thought. That's too bad, because choosing the right tire can be the difference between and a near miss and an accident. Getting the right tire for a vehicle starts with finding a knowledgeable dealer, one who can help you select the best tire for your needs. Tire retailers should also point out the pros and cons of each brand. The tire retailer should help you find the right tire for your car or truck.

Tires and Fuel Economy Choosing a tire based solely on fuel economy would be foolish, but according to Bill VandeWater at Bridgestone Firestone North America, "consumers can see a 15-20 percent difference in their fuel economy depending on the tire they select. Some studies have shown that many consumers like high fuel economy, but not at the cost of mileage or performance (especially wet)." Though many consumers consider fuel economy a high priority, it is typically not the number one priority for the consumer. Therefore replacement tires are not designed for with fuel economy as high a priority. According to VandeWater, "If a consumer wants a good fuel economy tire, the best choice is usually the original equipment tire. Consumers should also not forget that fuel economy is also dependant on proper air pressure. Monitoring air pressure regularly, and with proper inflation pressures as dictated by the vehicle owner's manual, is the best route to ensure maximum fuel economy.

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