Michelin Airless Tires or Tweels are highly durable zero maintenance tires, first introduced in 2005 as an alternative to pneumatic tires.
The word Tweel is a combination of Wire and Wheel, as Tweel does not use the conventional hub assembly. The inner hub is solid that mounts to the axle, surrounded by polyurethane spokes patterned as wedges. A band stretched across the spokes forms the outer edge of the tire. The air pressure of a traditional pneumatic tire is replaced by the tension of the shear band and the strength of the spokes. The tread of the tire is then attached with the shear band.
The spokes absorb the road impacts just like the traditional tires, but they deform temporarily, returning to the original shape once the force is removed. The Tweels can be customized to handle different situations by creating them with varying spoke tensions. More pliant spokes make for a more comfortable ride.
Polyurethane materials have remarkable properties, but they are not easy to make. Apart from the high costs, the manufacturing is difficult. Among other problems, the balance of friction and tread wear resistance is very critical. This also doubles their cost as compared to the standard steel and rubber tires.
The Tweels clearly are more practical for off-road applications. Check out this video for a demonstration: