Run-flat tires safety benefits outweigh problems.(CR Cars)

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.

[ILLUSTRATION OMITTED]

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 ...