Michelin's Airless Tyre: The Tweel

The first and possibly best example is Michelin’s Tweel. First announced in 2005, the Tweel derives it’s name from a combination the words “Tyre” and “Wheel” just as the Tweel itself is a combination of a Tyre and a Wheel, defying the normal wheel hub assembly. The Tweel consists of a solid inner hub which is connected to the axle. Surrounding this is a series of polyurethane spokes laid out in a wedge pattern. These act much in the same way as the air pressure in a normal tyre, absorbing the bumps and smoothing out the ride.

To give the tyre its shape and strength the spokes are secured with a shear band stretched across the outer layer of the spokes. By varying the tension of the band during the manufacturing process you can tweak the Tweel for better comfort or more responsive handling. It is this band that the tread is then attached to.

Advantages

The Tweel

The advantages of the Tweel are fairly obvious even from the first glance. The airless design eliminates the possibility of air leaks or blow outs at high speed for increased safety. And by taking the air pressure out of the equation you are left with more consistent and predictable economy and handling.

The flexible outer band increases the amount of surface area in contact with the road at any given time increasing the levels of grips. This would be particularly useful in off-road situations on rough terrain, and in use in the construction industry on uneven site surfaces.

Flaws

The Tweel is not without its flaws. From the offset, the design and manufacturing methods means they are not adjustable once they come out of the factory. So for better handling or better comfort you need to buy a whole new set of Tweels. An inconvenience, but not necessarily a deal breaker. Day to day most people will not find the need to alter their tyres once they have been optimised for every day road use.

What may be more of a nuisance is that at speeds in excess of 50 mph the Tweels vibrate very badly. This creates an awful lot of noise, which will be uncomfortable for passengers, as well as an awful lot of heat which could become an issue on long distance journeys.

The prototypes tyres are reporting to be yielding a one percent fuel economy against equivalent pneumatic tyres. Not good, but as time goes on this will surely be improved up to a level equal to, and eventually better than, regular tyres.

Initially Michelin are only rolling out Tweels for low speed applications such as construction vehicles, the iBot and the Segway Centaur. Possible military uses are also being explored.

Resilient Technologies Honeycomb Wheel

In the last few years however a competitor product has come forward. Resilient Technologies has developed their own “Tweel” using a honeycomb layout for the spokes instead of Michelin’s wedge. The company is reportedly looking at a 2011 push for these into the commercial and industrial market and are currently being tested by the US military. Consumer use models still seem to be a long way off.

Whatever happens, the next few years should certainly be interesting for advancements in tyre technology. This is one tech that is definitely worth looking out for.