Design Spotlight: The Airless Tire

Sometimes, we get so used to a certain product that no true changes are ever really made for years, decades even. Toilet paper comes to mind. Another is the pneumatic tire. Sure, the modern tire is a wealth of technology and high grade materials such as synthetic rubber, sulfur, carbon, steel, etc. Heck, recent years have even given us the run-flat tire, but the vast majority of cars don’t have these kind of shoes. Nevertheless, one requirement has always been the use of air, and if you’ve had your fair share of flats and blowouts over the years, you know how disconcerting your tires’ dependency on air truly is. Well, while you’ve been going about your day and no less, drooling away the night hours unconscious, tire engineers have been working hard at developing the airless or non-pneumatic tire.

Use of the non-pneumatic tire began in the 1970s for NASA on their Apollo Lunar Roving Vehicle. The Rover’s wheels were made with a spun aluminum hub and revolutionary airless tires made of woven steel strands coated with zinc. The traction requirements on the moon were obviously far greater given the atmosphere and terrain, so the contact area was partially coated with titanium chevrons. Needless to say, this kind of technology for earthbound applications would be unnecessary and prohibitively expensive (essentially, several dollars more than your entire ride).

Then, French tire company, Michelin, started their own development for the airless tire for passenger vehicles in 2005. Awkwardly dubbed the “Tweel”, this airless tire and wheel combination proved quite difficult to develop. The properties of a pneumatic tire enable adjustments in handling (lateral stability), ride quality (shock absorption) and noise reduction. The complete absence of pressurized air affects all three aspects. The Tweel was made of a thin synthetic rubber tread on the exterior, wrapped around a composite plastic band in order to provide road compliance and supporting and shock absorbing spokes made of polyurethane. The spokes, themselves, could then be manufactured at varying thicknesses in order to tweak the Tweel’s handling capabilities and the quality of the ride, from ultra firm to highly compliant. Finally, a rigid aluminum hub was used at the center, where the Tweel would be attached to the vehicle.

The Tweel’s construction setup allowed for solid structural support in place of air, along with significantly increased tread life, up to three times longer than a standard tire. Another huge benefit of the airless tire is the low cost of replacement since only the rubber tread needs to be replaced, rather than the entire tire/wheel structure. The first vehicles to demonstrate the new technology were an Audi A4 and a Segway Personal Transportation vehicle (blowouts on a Segway, a huge concern), though it was rumored that Michelin was planning first issuing their Tweel for military and construction use.

There’s evidence that the Airless Safety Tire was actually invented by a Mr. J. V. Martin of Garden City, New York. The Safety Tire utilized hard wood hoops encased in rubber, as well as hard rubber spokes that crisscrossed each other. It supposedly underwent successful testing but never saw any success. In the photo, you can tell that it is the clear predecessor to the Tweel and is executed in nearly the same fashion, albeit with different materials technology.

Michelin remained very secretive about the results of the Tweel’s testing and understandably so. For such a revolutionary project, there would’ve no doubt been issues with the tire. Some reports of excessive road noise and vibration at higher speeds were made public by those who drove the test Audi A4, which would make for a difficult sell to the driving public. Also, if Michelin was under contract with the military to develop such a Tweel for troop transport and combat vehicles, the information would’ve been documented classified. Potential competitors would naturally want to get their mitts on the findings, as well.

No real news of Michelin’s development of a military Tweel emerged over the course of the next several years. In fact, as recently as 2011, a company by the name of Resilient Technologies had made a move of their own and developed the NPT (Non-Pneumatic Tire) for military use and planned for testing with the government for what’s sure to be a lucrative contract. The claims are impressive, indeed. The spoke construction differs greatly from the Tweel spoke configuration, in that it makes use of a super-strong honeycomb structure. The NPT claims 100,000 mile tread life and is, more importantly, highly resistant to blasts.

Japanese tire company, Bridgestone, did research of their own and as recently as 2011, they released their own non-pneumatic tire concept at the Tokyo Motor Show. The construction of their version mimicked the Tweel almost exactly, with the exception of using inner and outer spokes that run in opposite directions, as opposed to the Tweel’s V-shaped spokes. Their claim was that noise and vibration for their version was a non-issue. Bridgestone’s strong showing is also a boon to environmentalism as the materials are far easier to recycle than standard synthetic rubber, hence the interesting green and black color scheme, most likely.

There are obviously still public perception, technical, economic and aesthetic issues to overcome. Is the consumer ready for an airless tire? From a safety standpoint, certainly. But we tend to dislike change, especially for a product we’ve used most of our lives. Frankly, most consumers don’t even understand tires to begin with. Throw width, diameter and aspect ratios at your average Joe, and his head starts to spin. We also like the looks of our tires, but probably more our shiny alloy rims. Take one look at the Tweels on the Audi A4, and you’ll see why they’re just not that attractive, bordering on just plain weird. Perhaps an actual sidewall to cover the spokes would eliminate this problem, but that could also affect the handling and noise properties of the tire. Also, how will the airless tire perform with dirt, debris or ice and snow trapped in the spokes? Finally, how much would an actual non-pneumatic tire cost? The manufacturers, and installers would have to completely retool, and the cost of manufacturing would no doubt increase the purchase price of the airless tire.

It’s uncertain how long it will take to see these available on the market, but we are no doubt headed in that direction for environmental and safety reasons. No matter what transpires, this new development in non-pneumatic tire technology will certainly be “revolutionary”.

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