It fell to another Scot, veterinarian John Boyd Dunlop, to “re-invent” the pneumatic tire in 1887 (his patent was later rescinded when Thompson’s was discovered). Its arrival coincided with the bicycle craze ushered in when the safety bicycle with two equal sized wheels was introduced. It made Dunlop’s tire a success because the air-filled tire had much lower rolling resistance and an immeasurably better ride.

Tire manufacturers, including Dunlop, soon emerged, and have been improving the pneumatic tire ever since. Today’s tires have a high level of performance but they can still lose air and go flat, immobilizing the vehicle. Engineers have tried overcoming this with run-flat tires, but they present their own problems such as weight, heat and a harsher ride. The ultimate answer is to get rid of compressed air altogether, i.e., to create the airless tire.

In this quest to eliminate flat tires and maybe even provide better vehicle handling and increased tread life, Michelin developed its “Tweel” (combination tire and wheel) airless tire that it announced in 2005. It had a thin reinforced outer band, like a tread or belt, and flexible plastic vee-shaped spokes that were attached to a small inner wheel. The load was supported by these spokes, rather than by compressed air.

Track testing was conducted with Tweels on an Audi A4, and apart from any technical advantages, the see-through wheels certainly attracted attention. Although optimism prevailed, it reportedly had such problems as excessive heat and noise, and higher rolling resistance than pneumatics. Not much has been heard of the Tweel recently. 

Now another tire giant, Japan’s Bridgestone Corp., has entered the airless tire arena with its “Air-Free” tire introduced at the 2011 Tokyo Motor Show. While still in the developmental stage, Bridgestone demonstrated 25 cm diameter Air-Free tires performing on light golf cart-like vehicles. Each tire-wheel can support 150 kg, and it brought back memories of the wheels on NASA’s Lunar Rover.



Bridgestone’s concept is similar to Michelin’s Tweel in that the chamber of compressed air is replaced with a matrix of curved and interlaced thermoplastic spokes between a reinforced rubber outer band and a small aluminum inner wheel. These spokes flex with wheel rotation to provide good ride qualities and vehicle dynamics, and can be engineered for different responses such as a more compliant ride or higher lateral stiffness for better vehicle handling. Work is progressing on scaling up the size for regular motor vehicles. 

Another player is Clemson University in North Carolina, where engineers are working on a heavy-duty, non-pneumatic tire for the military Humvee utility vehicle. It uses a heavy black rubber-like tread and plastic, geometrically shaped spokes.

A different approach to the non-pneumatic tire has been taken by Delaware-based New Tech Tire Corp., a division of Scitech Industries. Rather than wheels with flexible spokes, Tech Tire’s airless tire replaces the compressed air in a conventional tire with internal fibreglass ribs. Many advantages are claimed over the Tweel and Air-Free tires, including the ability to build it on conventional tire manufacturing machinery. 

Also, it is said to weigh the same as a pneumatic tire and can be mounted on a standard rim using regular tire shop equipment. New Tech says it has successfully lab tested its airless tire at typical highway loads and speeds for 10 hours.