Non-pneumatic tyres, also known as airless tyres, are not supported by air pressure. They are used on some small vehicles such as ride-on mowers and motorised golf carts, and on heavy equipment such as backhoes, which are required to operate on sites such as building demolition, where tyre punctures are likely.
Airless tyres generally have higher rolling resistance and provide much less suspension than similarly shaped and sized pneumatic tyres. Other problems for airless tyres include dissipating the heat buildup that occurs when they are driven. Airless tyres are often filled with compressed polymers, rather than air.
Michelin is currently developing an integrated tyre and wheel combination, the Tweel that operates entirely without air. Michelin claims its Tweel has load carrying, shock absorbing, and handling characteristics that compare favourably to conventional pneumatic tyres. The automotive engineering group of mechanical engineering department at Clemson University is developing a low energy loss airless tyre with Michelin through the NIST ATP project.
Resilient Technologies and the University of Wisconsin–Madison’s Polymer Engineering Center are creating a “non-pneumatic tyre”, which is basically a round polymeric honeycomb wrapped with a thick, black tread. The initial version of the tyre is for the Humvee and is expected to be available in 2012. Resilient Technologies airless tyres have been tested and are used by the US Army.
Bridgestone is developing the Air-Free Concept Tyre which is similar to the Tweel and can hold 150kg per tyre.
The Energy Return Wheel has the outer edge of the tyre connected to the inner rim by a system of springs. The springs can have their tension changed to vary the handling characteristics.