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Airless Tires


Tires that forsake their chief characteristic, being inflated, are in the pipeline of a considerable number of manufacturers: let us see why

Nicodemo Angì

It all originated in Greece, the cradle of Western civilization. The word "pneuma" is Greek and among its various meanings, we find: air, breath and even breath of life. The latter meaning has been abundantly used and expounded on by philosophers and theologians, not only Greek:  Pre-Socratic philosophers used it in the sense of “soul” as a principle of life, and Christianity also uses the word “pneuma” much in the same fashion as Judaism does, as spirit, or even Holy Spirit.

Nowadays the meaning of the word “pneumatic” has totally lost its philosophic and theological implications in favor of something that simply deals with air: therefore we now talk about void or thin air, compressed air-operated machines (pneumatic drills for example), and more importantly pneumatic tires, or simply tires as we are accustomed to call them. Hence, why are we rejecting this well established fact, producing and marketing airless tires?


Why airless?                                                       


A tire of this type has several advantages, the most important being its durability: the word “puncture” loses its negative implications since, even if a hole should accidentally be produced, nothing would come out of it, and by the same token the sidewalls would also be sturdier as they barely exist. A further “ace up the sleeve” relates to the greatly reduced maintenance needs and procedures as elements such as valves and the already rare inner tubes are eliminated altogether.

In terms of set-up and ability to cope with the roughness or asperity of the roads, the lighter structures, made possible by synthetic materials replacing the more traditional metal wheels,  as well as lower un-sprung weight, will prove to be extremely beneficial and promising. Pneumatic tires, in reality, were not the first “tires” to be used: initially they were made of solid rubber as a simple cover for cart or carriage wheels. Towards the middle of the 19th century, long before the automobile age, a number of patents involving inflatable tires had already been deposited, and with the discovery of the curing process and carbon black, soon became the talk of the town. Solid tires have benefitted from technological advancements over the years, but their use, given the limited levels of comfort, has always been restricted to specific sectors, for example, on industrial vehicles or trolleys, which are not meant to be used on roads.

It is no coincidence then, that new generation airless tires have found their first commercial application on industrial vehicles, with the goal of combining the reliability of solid tires with the comfort of inflated ones.



On the market!                                                    


Tweel is the name! A Michelin project that comes with a semi-rigid shear beam connected to the wheel by high-strength poly-resin spokes. The steel hub boasts eight standard mounting bolt holes and is designed for the following uses: small mechanical shovels, skid-steer loaders and lawnmowers. The Tweel SSL is available with an all-terrain tread pattern as well as a 12,1inch hard surface, while the Turf version is designed to equip John Deere’s Ztrak 900 B, M and R lawnmowers, with a 10,7 inch section and a special tread that prevents turf damage. The Michelin web site contains videos that compare the behavior of the Tweel with that of air filled radials as well as solid tires. The behavior of the Tweel is very similar to air filled radials – i.e. very comfortable, and less strenuous on the vehicle – maintaining the same reliability of solid tires, which for their part have a tendency to jolt.  

A very different, yet still specialized application is the Sportsman WV850 H.O. Quad-bike, produced by Polaris Defense, to be used also for military purposes. The Sportsman WV850 is equipped with Airless TerrainArmor tires, with a polymeric web design and a cast-alluminum hub. They come in 26x9inch size and guarantee breakthrough durability and performance even if hit by AK47 or 0,5“ bullets (the Defense version!).

Britek too, has a commercial production, but in this case we are talking of pre-assembled bicycle tires; known as Energy Return Wheel, once compressed, by the many bumps on the road, the internal rubber layer returns the elastic potential energy stored within the wheel and converts it into forward momentum.


Premium brands at work                                  


Other companies are likewise developing their own NPT (Non Pneumatic Tires) although still not available on the market. Hankook’s iFlex seems well on its way and has recently been put to the test in five different categories, durability, hardness, stability, slalom and speed (up to 130 k/h). Detailed specs are still missing, though some information issuing directly from the manufacturer talk about a compressible web boasting deep cavities on the tread. The iFlex represents a switch to a more eco-friendly material that makes end-of-life recycling easier.  

Bridgestone is likewise engaged in studying and developing its NPTs: the AirFree with its unique structure of spokes stretching along the inner sides of the tire in opposite directions is the Japanese giant’s proposition. The latest version was unveiled during last year’s Paris Motor Show and one of the company’s engineers confirmed that the company is still working to increase the tire’s load capacity (in Paris they were mounted on a light – and slow – electric cart) and improve the tendency to accumulate waste material between the spokes, which undermines the tires ability to absorb shocks.

In conclusion, at the end of this brief review, we can safely assume that experiments and field trials are quite interesting though not conclusive. Doubts remain about the possibility to manufacture NPTs suitable for very high performance vehicles: the diameter of these airless tires cannot be reduced much further and this could be a problem when it comes to producing low profile tires. With this in mind, is there anyone up for the challenge?

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