Just as we're getting used to run-flat tires, which means you run them flat for 50 or 100 miles before repairing or replacing them, along comes an airless tire. It's called Tweel, from Michelin, and it's a thick band of rubber (essentially the tire tread) applied to a wheel with deformable spokes. With a normal tire, when you hit a bump, the tire flexes (as does the suspension), but not the wheel. Hit a bump hard with low-profile tires (tiny sidewalls), and your expensive alloy wheel flexes – actually, it breaks, as may the tire itself.

With Tweel, the polyurethane spokes flex instead of the tire sidewalls. Because the tires are air-free, Michelin says lateral stiffness can be increased by a factor of five. Translation: When you corner hard (or accelerate, or brake), a traditional tire deforms and the tread loses some of its grip. Increase air pressure from 32 psi to 45 psi, and the tire deforms less, but ride quality goes down the drain. With Tweel, that's a non-issue.

Prototype vehicles are noisy, so there are no immediate passenger-car plans. Tweel might come sooner to commercial vehicles or the military: Imagine a Hummer that wouldn't be stopped by spikes in the road.

For Michelin, Tweel could be an end-run around the run-flat tire issue and the need for costly tire-pressure monitors. Competitor Bridgestone's run-flats work on any wheel; Michelin run-flats require a separate wheel system called PAX, and tire buyers with long memories recall an ill-fated, proprietary 1980s Michelin wheel specification called TRX that locked buyers in to one brand and a handful of tire choices. On the other hand, Michelin had another radical concept that worked out well, eventually: the radial tire.