The bad news is, new technology is altering Homo sapiens' evolution such that, in one generation, few of us will know how to change a tire, a basic skill man has been performing for millions of years. Still, the technology shows progress in our species. The spare tire is disappearing, and standard equipment nowadays is more likely to be a canister of tire sealant—or a cellphone to call for roadside repair. Unless, of course, you have run-flats.
A cross section of Bridgestone's run-flat tire shows how steel and rubber combine to keep you rolling. For 50 miles, anyway. (A) Molded fins on the outer edge draw heat from the tire so it lasts longer. (B) Reinforced sidewalls keep the deflated tire from collapsing.
Wait, what are run-flats?
A run-flat tire will run, uh, flat for 50 miles at 50 mph, enough to get you to a repair shop. It's built with stiff sidewalls so that even when deflated it can support the car. Though the technology has been around since the 1980s, the Bridgestone Drive Guard is the first to really go mainstream—and at a price that's comparable to an equivalent touring-grade tire ($100 to $200).
Can I put them on my old Honda Accord?
Perhaps. Run-flats should be installed only on cars that have a tire- pressure monitoring system (TPMS) that alerts the driver to a pressure decrease. That includes most new passenger cars since 2008, though the system can be retrofit on older cars.
Is it as good as a normal tire?
Earlier generations of run-flats were too heavy, too noisy, and not durable. But the DriveGuard has a taller profile that yields a better ride. We maneuvered a Toyota Camry equipped with them through a tricky course with a deflated front-left tire. One tight corner would have pulled a flat standard tire off the rim, but the DriveGuard stayed put. Well, kind of: Bridge stone had painted a mark on the tire, so you could see that the tire had slipped a little around the wheel rim, something the engineers said is acceptable. It pulled a little under braking, and there was noticeable noise, but not the flapflapflap of a typical flat. On a wet course we found traction on both DriveGuard and Bridge stone's traditional Turanza to be the same.
If it works so great, how will I know I have a flat?
The tire-pressure warning light on the dash glows.
What happens if I just keep going?
In a deflated run-flat tire the internal fle generates lots of heat, which destroys both the rubber and the underlying steel-and-fabric structure. DriveGuards feature something called cooling fins molded into the sidewalls to disperse heat. Still, they're pretty much toast after 50 miles.
So, I can't fix it?
Probably not, unless it's just a puncture in the tread and you caught it early. In most cases you'll need a new tire.
Does this mean I don't need a spare?
Well, neither run-flats nor sealant-and-compressor kits can fix a bent rim. Plus, run-flats typically have a lower profile, so they provide even less rim protection. If you break a rim, you'll miss having a fifth wheel, so if you're buying a new car and a spare is available as an option, get it. And if you see a teenager, show him how to change a tire. For the good of the species.