Airless Tyres: Pros and Cons
A flat tyre is one of the greatest inconveniences a motorist can suffer; in addition to causing lengthy delays or expensive towing costs, severe rupture of a tyre at speed can cause a serious or even fatal accident. Standard tyres cannot be safely driven on when flat; they cause the rim of the wheel to directly contact the ground or the remainder of the tyre with severe detrimental effect on vehicle control. This means that drivers are often stranded, especially on a motorway hard shoulder or other place of risk.
To alleviate these problems, manufacturers have devised airless tyres, which come in various forms. The ‘run flat tyre’ has been fitted as standard on several brands of luxury car such as the BMW in recent years. The tyres are self-sealing, with a layer capable of shoring up any puncture that occurs and prevent any significant air loss: this offers immediate benefit in that should the tyre become ruptured it is still safe to drive on for up to 50 miles. This allows the driver to reach a safe stopping point or to locate tyre fitters and have the tyre repaired or replaced. By removing the need to carry a spare tyre and accompanying heavy tools, run flat tyres can also offer improved fuel economy, which is particularly attractive in times of escalating fuel costs. Indeed, for the fortunate driver who avoids a puncture, costs saved can more than offset the increased tyre price.
However, run flat tyres are not without their cons – the price is hefty, up to double the cost of a standard pneumatic tyre. For luxury brand car owners in particular, where tyre costs are already at a premium, this can be extremely expensive. Ride comfort is also often quite poor, due to inflexibility in the tyre wall. This is especially marked at high speed or when performing a sharp turn, and can be discomforting.
A second form of airless tyre is the ‘Tweel’. Devised by Michelin in 2005, this is a completely different concept. The outer edge of the tyre is a strong rubber (polyurethane) band, which is stretched around an inner supporting set of polyurethane spokes. The alloy wheel is then fitted centrally within this ring, providing a highly supportive wheel without the need for a conventional tyre.
The Tweel is designed so that the spokes absorb any impacts. By varying the tension of the outer ring and the design of the spokes, it’s straightforward to alter ride handling according to the driver’s requirements. By avoiding use of an inflated tyre, the wheel cannot burst or get a puncture. Whilst this approach may therefore seem to remove many of the associated problems of a conventional or run flat tyre, the Tweel has been described as performing quite noisily and suffering from excessive vibration, especially at high speed. However, as of mid 2013, this type of tyre is still in development, giving the developers time to work on refinements and reduce these road noise problems.
Airless tyres thus appear to provide many benefits compared with the traditional pneumatic tyre. However steep costs and handling issues remain with both forms devised to date, hence the basic tyre still has plenty of life left in it at present. In the future, it appears certain that this new breed of tyre will ultimately provide a great solution for road users.