Conventional pneumatic tires use air pressure to maintain their shape and resistance to weight and driving forces yet also cushion the vehicle from road imperfections. Principle 29 – Pneumatics and Hydraulics
Michelin has developed an airless tire called the Tweel. This is a merging of tire and wheel into an integrated unit. Principle 5 – Merging
Because they cannot burst or lose air pressure, Tweels tend to be far more durable than pneumatic tires. Principle 2 – Taking Out
The Tweel uses polyurethane spokes which provide similar compliance to inflatable tires. Different handling and ride characteristics can be produced by carefully configuring the layout of these spokes. Air pressure within an inflated tire is distributed in all directions, but the ability to tailor lateral stiffness independently from vertical stiffness makes it possible to have compliant ride and great cornering, braking and acceleration. Principle 3 – Local Quality
From a driver comfort perspective, the main limitation of current Tweel implementations is that they are quite noisy at high speeds.
Another problem stems from the merging of wheel and tire. One of the most common tire sizes in North America is P235/75R15, which is to say 235mm tread width, sidewall height 75% of the tread width, sized to fit a 15 radius inch rim. There are countless permutations of these specifications. The rims themselves also vary in radius, offset (how far they stick out from the hub), width and bolt pattern. To meet the needs of the automotive market generally, the Tweel would need to be produced in an staggering number of configurations.
Segment that market
Given the pros and cons of Tweels, it is understandable that they have found a home in limited markets. Principle 1 – Segmentation
The Tweel’s durability makes it a natural fit for military and construction vehicles, skid steers, riding mowers and forklifts.