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Tubeless Tyres - A Sleepy Hollow

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Saturday, 01 August 2009 14:30

It has been over a century from the time Dunlop patented his 'mummified wheel' to the modern radial tyres of today. Yet with all the improvements a tyre has undergone, one thing remained unchanged, which is only when it is inflated to the optimised level and that inflation is kept constant that it can deliver maximum comfort and performance.

It may come as a surprise to many readers that in 1903, engineer Paul Weeks Litchfield, then in his early 20s, was granted a patent for the first 'tubeless' tyres. He later rose to be the chairman of the Board of Goodyear in the year 1940. Just like many other patents, which were granted during that period, this concept was not pursued until late 1939 when the requirement for the first amphibious tyre was felt. The 120x33.5 - 66 smooth tread Marsh Buggy tyres, by far the largest tyres produced then, were used on Admiral Byrd's Snow Cruiser. This vehicle was capable of carrying very heavy loads over all sorts of terrain, even float on water. These were off-the-road tyres, flexible but inextensible pressure vessel that were pre-stressed and skin-stressed by air pressure. To produce such tyres Goodyear at Akron employed the idea of Litchfield, using nylon cords for the first time and a newly developed synthetic rubber compound called Chemigum to line the inner casing of this tyre to lighten its weight and eliminate the tube.

The Second World War highlighted the need for reliable tyres as loss of air or punctures cost precious moments or even endangered lives. Though the tubeless concept was not used during the war, subsequent development of tyres with a 'run-flat' capability by introducing tubes, which had a special construction of a sealant on the lower side, this allowed it to run without an air loss even after a penetration. The added weight of the tube made the steering wheel heavy and restricted speed. They were used on low speed trucks, which traveled on areas with puncture hazards like wrecker's equipment, dock and warehouse vehicles, and other utility trucks.

To reduce weight lifeguard tubes were introduced, having two air chambers, the outer rubber tube with a thick canvas tube inside. In case of a blowout only the outer chamber gave way, while the reserve air in the thick canvas tube would not allow the tyre to be completely deflated allowing the vehicle for a safe straight line gradual stop.

After the war a more determined effort towards elimination of the inner tube was sought as it was considered the main source of service trouble and failures while being clearly superfluous and costly. Experiments were therefore conducted both in the USA (initially by Goodrich) and in UK (by Dunlop), towards providing a near perfect seal between the tyre bead and rim, under all service conditions. This meant that the tyre had to run even at low inflation pressures or with a penetration to a safe distance without loss of vehicle control. It was in the year 1954 that the first commercially realised tubeless tyre was fitted as original equipment, by the now defunct Packard marque.

During the mid 1950s and early 1960s, India too manufactured tubeless tyres, which were not only supplied as original equipment for the cars, but also had a number of sizes meant for the replacement market. While the rest of the world accepted this new technology and by the middle of 1962, nearly all commercial vehicles, trucks and passenger cars used tubeless tyres, we in India reverted to the old tube-tyre theory. Even though most companies in India still manufacture tube-type tyres, many have the tubeless technology available with them and do manufacture tubeless tyres meant for export only.

Tubeless tyres have reappeared in the Indian scenario but many users are reluctant to use them. Some fit tubes in them. So which is actually better? Let us see where the construction difference lies. Apart from the basic construction, which remains the same with the run of the cords distinguishing the type of tyre construction, whether it is a cross-ply or a radial ply one; the main difference lies in the application of the inner liner of the carcass. Whereas in a tube-type construction the inner liner acts as a medium for reducing friction between the cord body and the tube, in a tubeless construction this is the tube itself. Thus the inner liner in a tubeless tyre is made up of a Halogenated Butyl rubber like Chlorobutyl or Bromobutyl for better air impermeability together with high heat and weather resistance.

Though compounds used in a tubeless or a tube type tyre may vary, the other major difference lies in the bead area of the tyre. While considering a radial tyre both type of tyres have a flexible yet rigid bead, where the bead bundle is very thin and the stability of the tyre is enhanced by the bead apex or bead filler controlling it, in a tubeless it also has to maintain the air pressure within. Thus the bead heel in the tubeless sits more tightly within the flange of the rim, and to ensure this tight fitting most tyre manufacturers add an extra wrapping over the bead area. This enhances high-speed performance while achieving a better cornering ability on the tubeless.

The other advantages are the absence of a tube make the tyre lighter in weight, thus has less chance of vibrations, which means that it leads to a better fuel saving. Even the rolling resistance in a tubeless radial is lower when compared to a tube type radial. This is due to the fact that the tubeless tyre sidewall is more supple as there is no internal body to create a friction. This also helps the tyre to run cooler as it eliminates heat generation caused by the internal shuffling of the tube.

The inner liner also acts as an absorbent during a nail penetration making the nail act like a plug and therefore the tyre has a slow leak and not a sudden deflation as it occurs on a tube- type tyre. This can be illustrated by a simple example. Pierce an ordinary balloon with a pin and it disintegrates, while sticking a cello tape on the balloon would enable the pin to penetrate without it bursting.

Similarly by comparing a tubeless tyre to a balloon that is not fully inflated, when squeezed this would deshape to certain extent before it bursts. Thus a tubeless can flex over an object, giving it a better impact resistance than a tube type one.

Personally, I feel that a tubeless tyre is more beneficial than a tube type tyre, but yet many people feel that since a local puncturewalla cannot attend to a tubeless it may be a bad proposition to use them. Generally it is quite simple and sometimes easier to repair a tubeless tyre than a tube type one. Of course there still remains one important criterion that the repairer must have proper tools and equipment to handle the same, which is essential for tube-type tyres as well. I still maintain that utmost care and regular checks should be carried out at regular intervals to get the best from your tyres. Secondly most tyre companies worldwide do not recommend use of tube in tyres lower than 60 aspect ratio. The other factor is the safety given by a tubeless may not be comparable with a one using a tube, as my case study will show.

Author: Sujon Chaudri

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