Some tires are so sophisticated that they require a special system to enable them to communicate with the driver and/or other automotive systems. The following tires and systems fall into this category.
Run-flat tires can be driven on without any air pressure inside the tire! This means that you don’t face the stress and danger involved in having a blowout or changing a tire at the side of the road.
Run-flats can be constructed in two different ways: Self-supporting run-flat tires have stronger sidewalls to keep the tire from collapsing if the air pressure inside the tire drops. Layers of rubber and heat-resistant cord, and sometimes support wedges, are used in the sidewall.
The PAX system designed by Michelin allows you to drive up to 55 mph for up to 125 miles with zero air pressure inside a tire! The system includes a tire, a tire-monitoring system that measures the temperature and the pressure of the air in the tire, and a wheel with a strong inner ring that supports the tread if the tire loses half its air pressure.
Unlike most other tires, the system also features a special anchoring mechanism that keeps the tire on the wheel if the air pressure in the tire drops. Michelin claims that PAX system tires wear longer and get better fuel economy than traditional tires because of reduced rolling resistance.
If the tread area is punctured, the tire can be repaired and the support ring reused. You can read more about this system
Under normal circumstances, properly inflated run-flat tires should last the same 30,000 to 40,000 miles as many ordinary tires. You can drive run-flat tires with no air pressure in them for 50 to 125 miles at speeds up to 50 or 55 mph without further damaging the tire.
Although run-flats are durable, running on them without air at high speeds for a long period can damage them. Because the driver often can’t feel any difference when a run-flat goes flat, automakers incorporate low-pressure warning systems to alert the driver that a tire has lost pressure and to drive more slowly and get the tire repaired as soon as possible to avoid further damage to the tire or wheel. See the next section for more details on these warning systems.
Some run-flat equipped vehicles may not even come with a jack or spare tire! Although run-flats are durable, there’s always the chance that one can be disabled by a defect or accident, so if your vehicle lacks this equipment and has room to carry it, I strongly suggest that you buy yourself a jack as well as a small, temporary spare tire in the correct size for the wheels on your vehicle. By being prepared, you save yourself a tow and/or a long wait if the dealership doesn’t have the proper tire in stock.
Forewarned is forearmed! Although you can have run-flat tires installed on a vehicle that didn’t come with them, you also need to purchase a warning system designed for the new tires, and if the rims on your current wheels aren’t sturdy enough to accommodate run-flats, you may have to replace those, too. Also be aware that vehicles that come equipped with run-flats have suspension systems that are tuned to the rigidity of the sidewalls.
So if you replace the tires on a vehicle with a standard suspension with run-flats, there may be a difference in the way your vehicle handles, and the ride may be a bit harder and noisier.