Saturday, October 9, 2004
No fuss with run-flat tires
By Carol Traeger
A run-flat tire is demonstrated on a car equipped with a PAX system from Michelin.
You're slogging peacefully along Interstate 75 on a rainy morning when, "Kabam!" - you limp to the shoulder with a flat tire. Trucks roar past, kicking muck all over your suit as you remove the spare and furiously work the jack. You arrive late to your business meeting, frazzled and looking like something the dog dragged in from the lake.
If your vehicle had been equipped with run-flat tires, you could have avoided this scenario altogether.
Run-flat tires can support an un-inflated tire in an "inflated" position for anywhere from 50 to 150 miles, at speeds up to 55 mph. That's plenty of margin for getting to work on time and/or to the safety of a service station.
The Chevy Corvette was the first production vehicle to be equipped with run-flat tires, back in 1993. Today, about 16 models are available with run-flat tires, including the Mini Cooper, Toyota Sienna, the BMW 3-Series, Dodge Viper, Cadillac XLR, Infiniti Q45, Lexus SC230, Honda Odyssey and the Rolls Royce Phantom. Volvo will offer run-flats on its 2005 S60, S80 and V70 models.
If run-flat tires perform nearly as well un-inflated as they do inflated, how do you know if your run-flat tire has a "flat" (so to speak)? Every car with run-flat tires must be equipped with a tire-pressure monitoring system, which alerts the driver - via sight or sound - if it detects low tire pressure. Beginning in 2006, tire-pressure monitoring systems will become mandatory on all new passenger vehicles sold in the U.S. - which in turn should make run-flat tires more widely available.
Currently, there are two types of "run-flat" systems: self-supporting and Michelin's PAX system.
"Self-supporting" run-flats, which have super-strong sidewalls capable of supporting an un-inflated tire, are the most commonly used by tire makers, including BF Goodrich, Bridgestone, Dunlop, Firestone, Goodyear, Kumho, Michelin, Pirelli and Yokohama.
Michelin's PAX system uses an inner ring (instead of stiff sidewalls) to support the tire in the event of lost air pressure, allowing the vehicle to travel at 55 mph for up to 125 miles. A specially designed bead prevents the deflated tire from separating from the wheel even when going through autocross-style maneuvers. In addition to sparing drivers the inconvenience and dangers of flat tires, PAX tires create less rolling resistance than radials, resulting in better fuel economy.
The 2005 Honda Odyssey just became the first mainstream vehicle in the United States to be offered with Michelin's PAX System. (The PAX System has been standard on the Rolls-Royce Phantom in the States since 2003, and it is available on several Audi models sold in Europe.) Since introducing the PAX System in 1998, Michelin has licensed the technology to Pirelli, Goodyear, Sumitomo Rubber Industries and Toyo.
Because special equipment is needed to mount and dismount PAX tires, Michelin is setting up a nationwide network of PAX-approved service locations, including independent shops and Honda dealerships. It has established a 12-hour delivery assistance program.
Not all garage's and tire dealers are equipped to repair run-flats, but those that are charge anywhere from $15 to $45.
It's possible to retrofit a car with run-flat tires, but there are some important factors to consider:
Harsher ride: Putting run-flats on a vehicle originally shod with regular tires will result in a harsher ride, more tire and road noise, and possibly give the car different tracking. New cars offered with run-flats have suspensions designed to accommodate the tires' different characteristics.
Expense: Run-flat tires cost more than regular premium tires, ranging from $175 to $350 per tire. If your car doesn't have a tire-pressure monitoring system, you'll have to buy and install one, which will run you from $250 to $300.
Mounting procedure: Some run-flats must be mounted on special rims (check with the dealer), and all run-flats require a different mounting procedure, so always have them installed by a factory-authorized dealer.
Rolling into a safer future
By far the biggest benefit of run-flats is safety. They make our roadways safer by reducing the risks of losing control if a tire blows out, and by enabling you to drive safely to a service station.
Automakers benefit, too. By eliminating the need for a spare tire and a place to carry one, run-flats reduce weight and allow more flexibility of design, which can cut production costs.