TRADE-OFF   Run-flat tires maintain their shape after air loss (above, right) and can be a great convenience and a safety asset compared with regular tires. But some run-flats are very expensive to replace, and replacement models are limited. Graphics courtesy of Bridgestone Corporation

Tires that can be driven on for 50 miles or more with no air in them enable drivers to get to a mechanic without having to change the tire after a puncture. Run-flat tires are more than just a convenience; they can add a measure of security by eliminating the need to change a tire in bad weather or in dangerous roadside areas.

While run-flats--which are increasingly common on new vehicles--provide substantial safety benefits, they have some disadvantages, which can be glossed over in the car dealership. Some owners of run-flat tires have complained of premature or uneven wear, a stiff ride, high replacement costs, and limited replacement choices. Some owners also say they want the added security of a spare tire, and cars with run-flat systems don’t usually carry them.


WHAT THEY ARE

Run-flat tires come in two basic types: Self-supporting tires, as found on vehicles like the Toyota Sienna and Chevrolet Corvette, have very stiff sidewalls to maintain their ability to carry the vehicle load after air loss. But the added stiffness can lead to a harsh ride. The Michelin PAX System, used on the Honda Odyssey Touring, uses a special wheel with a ring on it to help support the tire without air. But changing the PAX requires equipment that many dealerships don’t have. Some owners simply choose to swap out the tire and wheel combination after a flat, which adds to the cost. Plus, owners report that those assemblies aren’t always in stock.

Some vehicle owners have complained on the Internet that they were unaware their cars had run-flats when they bought them and only found out when they had to replace the tires. Some all-wheel-drive Sienna owners gripe of needing a new set after just 15,000 miles, at a cost of $800 or more. Conventional all-season tires typically last 40,000 miles or longer, and most cost less.

Toyota says that the wear problems have been fixed on newer models and they have extended the tire warranty on earlier models. Consumer Reports has purchased an all-wheel-drive Sienna with run-flats and is currently testing the tires.

Run-flats are found mostly on higher-end sports cars and sedans and models with limited space for a spare. They have recently moved into the minivan segment. Owners of high-performance cars might not object to the stiffer-riding sidewalls of run-flats, since most of those cars ride on stiff tires to begin with.

The bottom line. Despite the disadvantages and inconveniences of run-flat tires for many, Consumer Reports believes that the safety benefits can outweigh the downsides. And the technology behind them is improving while prices are coming down.

Consumer Reports also recommends that you know what kind of tires a car comes with before you consider buying it.