During most of the automobile’s recorded history, cars carried spare tires—sometimes in the early days, several of them (because of frequent punctures) in twin sidemounts or out back. Along with the tires as standard equipment was a jack (often in several pieces) and a jack handle. Part of driver’s ed was learning how to change a tire—don’t forget to use the approved jacking points!
I mention all of this because spare tires and jacks may soon become part of history. Not only are today’s cars being shipped with temporary spares (good for 50 miles or so) but the jack has been largely jettisoned. These steps are being taken to save weight—which is particularly important in heavy electric cars. Many cars today have no spare or jack, and come with small air compressors that work in concert with spray sealant to temporarily repair a flat. Or that’s what is supposed to happen—I’ve never successfully used that combination.
And another reason why jacks will soon be seen only in thrift shops is the run-flat tire. As the name implies, run-flats resist deflation and can keep you on the road after a puncture. The idea goes back to 1934, when Michelin introduced a tire for commuter trains and trolleys that had a “safety rim” inside that could run on a foam lining after a puncture.
Passenger cars got run-flats in 1958, when Chrysler and Goodyear teamed up on Captive Air tires. In 1972, Dunlop introduced the Total Mobility Tire and it became standard on certain Rover models. In a typical self-supporting run-flat today, the reinforced sidewall stays rigid without air pressure—and (as with compact spares) you have 50 miles of safe driving ahead before they should be removed and repaired.
Ian McKenney, a spokesman for Bridgestone, said in an interview that the DriveGuard line was launched in 2014 as the company’s first run-flat line, and has now been updated as DriveGuard Plus touring tires. Run-flats are generally 20 to 40 percent heavier, but McKenney said that running them eliminates the need to carry a spare—providing a 50-pound weight saving, plus the jack.
McKenney said that when a tire is punctured and goes to zero pounds per square inch inflation, rubber inserts in the tire keep its shape and stay on the wheel. “You can drive 50 miles at up to 50 mph,” he said. “It will get you home or to the tire shop. Driving any further than that is not recommended, because as the tire rolls it compresses and that compression generates heat—the enemy of rubber. The tire will lose its chemical integrity and soften.” Certain types of damage to run-flats—as in sidewall punctures—may not be repairable.
Not many new cars come with run-flats, but Bridgestone has an arrangement with BMW, most of whose models are so-equipped. Cars that come with run-flat tires also have Tire Pressure Monitoring Systems (TPMS) because otherwise you might not even know the tire was impaired.
The DriveGuards, with a 65,000-mile wear warranty, come in 19 sizes. “They’re an excellent touring tire that just happens to be run-flat,” McKenney said. Curiosity about Bridgestone’s DriveGuard run-flats led to this test. I have old cars with smaller tires, so the test DriveGuards went to my friend Ko Denhamer near Philadelphia, to try out on his 122,000-mile 2003 Saab 9-5 Linear wagon with manual transmission.
Ko reports putting close to 1,000 miles on the DriveGuards during the extra-hot July and August weather. The tires were inflated to 35 psi front and 32 psi rear, as per the Saab manual. Ko compares them to the Michelin Pilot Sport A/S 3 tires that were on the wagon previously.
“I’ve run the Bridgestones on a mix of running errands around town and twisty winding backroads as well as highway driving at temperatures of up to 100 degrees Fahrenheit and up to 80 mph,” Ko said. “We’re in a drought, so the roads were mostly dry, though there was occasional light rain. Some rough road surfaces were encountered.”
Ko says the tires are similar to the Michelins in providing a comfortable ride, as well as the same quiet operation. “Good cornering, and I think the Bridgestone DriveGuard Pluses may actually feel slightly more planted and solid. All in all, great handling and comfort I really wouldn’t know they’re run-flat tires if I hadn’t mounted them myself. There’s not a trace of hard handling or stiffness. They’re really a good all-around tire with the benefit of run-flat safety built in.”
Ko also notes that when he removed the Saab’s now-unnecessary spare “it had zero tire pressure. The valve stem had failed. With run-flats I won’t have to worry about that.”
Run-flat tires won’t be for everyone, but in an auto environment where weight is critical they’re likely to have a future. The next step is solid tires with no air in them at all—Michelin showed such a VISION tire at its Movin’ On event in Montreal in 2019, but actual commercial production is still in the future.