TUBELESS TYRE TECHNOLOGY

1. INTRODUCTION

            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. This is one of the basic reasons all tyre manufacturers try to focus on in the development stage of a tyre which can have the best air retention ability. Usage of a tube or an extra air container within the tyre was regarded as the best solution for many years

            It may come as a surprise to many 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.

2. THE TUBELESS REVOLUTION –

What Makes A Tubeless Tyre? We Explain.

In this epistle we focus on the constructional details of a tubeless tyre which will fundamentally help us as we motor along the tubeless highway.

It is tragic that we Indians are not the hardiest of adventurous souls who experiment and adopt new ways to spice up their life, and also to make things easier on themselves. Though tubeless tyres have been around since the mid 1950s, we only stumbled upon them with the advent in the late 1990s! It's another matter that it needed a high-end premium automobile to set things rolling on this count - a case repeated often enough abroad as well - but now we need to see the same thought and product process filtering through lower down the pecking order. Many car makers and tyre makers blamed bad roads and a lack of education as reasons for not ushering in tubeless tyres but all that is now changing. It better because our neighbours in the SAARC nations like Sri Lanka, Bangladesh, Pakistan and Nepal have been running on tubeless tyres for over a decade, if not more!

In place of the tube in a normal tyre, the tyre and the rim of the wheel form an air container in a tubeless tyre. To 'seal in the air', in this tyre-rim compartment, the inner wall of the tyre is throughly lined with an impermeable, air-tight membrane. The inner liner of the tubeless tyre is constructed of halo-butyl/chlorobutyl and other materials. This performs, in essence, the important chore of substantially reducing the permeation of air, as compared to the natural rubber inner liner, a function of which is why we use a butyl tube in a tubed tyre.

A tubeless tyre also comes with a soft rubber chaffer, distinct from a rubberised fabric chaffer in a tubed tyre. This works as an all-round air seal between the tyre and rim.

As there is no tube, and, hence, no tube valve, a specialised valve is employed for increasing/reducing the air pressure in a tubeless tyre. The valve (check out the line drawing to see how it mounts) sits on the tyre rim and is ingeniously sealed by a large high quality rubber seal which is easy to mount.

As you can see that the tube is integrated in the tyre construction, so to spead, you also have less weight, helping handling engineers in the car companies realise the benefits of low unsprung weight. If you drive a Toyota Qualis or a Mercedes-Benz C, E- or S-Class, or even the stunning new Ford Mondeo, the benefits of the tubeless rubber they come with would have passed you by, so good is the feeling.

3. THE TUBELESS REVOLUTION –

From the cross-ply to the radial to the tubeless

            In the days of yore the only Indian cars worth considering were the only cars available. As an impressionable youngster who used to hang around car enthusiasts, I used to always hear that this tyre is no good because it could do only around 20,000km before the tread vanished. Tyre life over all else seemed to be the mantra of the everyday car user and I remember even our family car, which used to be a Hillman Minx then, would seemed to go on and on forever.

            Things changed dramatically in 1980s with the advent of the Marutis and also the ushering in of the radial revolution. Suddenly we started hearing things like grip and steering responses and ride comfort and fuel efficiency and not just tyre life.

More than anything else, it was growing awareness levels among car users that saw many veering towards the radial tyre. The compromise between comfort (radial deflection), and steerability (sideways stiffness) was not possible with the traditional (read that as cross-ply) tyre structure as with the radial ply tyre. A radial casing alone offers no improvement but if it also comes with a reinforced belt structure it retains the high comfort factor of its radial-ply nature with the added virtues of steering controllability.

            Moreover, it allowed designers to adjust the two factors in relation to each other as required for a particular type of car. In contrast to the radial, the cross-ply is now comparatively limited as far further development is concerned, even in India. I qualify this by suggesting this statement holds good for passenger car application tyres only.

            Radials may be about 25 per cent costlier than similar sized cross-ply tyres but they may give upto 8-0 per cent more mileage and also afford the other intangible benefits in superior ride quality and better grip and control, factors which have become common-speak even in India today.

            With the advent of radials came the stylised looks as well. Of course this came thanks to the wide squat rubber used by racing cars but automotive stylists were quick to pick these cues and design them into their new automobiles. The designers wanted wheels of a certain overall diameter but they wanted them to also accommodate the brake discs and part of the hub carriers. This helped give us the lowered height-width ratio and even though we have had low profile cross-ply tyres as well, the radial handles low profiles infinitely better-just ask Ferrari or Mercedes-Benz or BMW or Porsche.

            It was this battle for low profiles and great grip with better cornering stability which brought the tubeless tyre to the fore. In the early days thanks to rubber compounds and tyre constructions being at the technological levels prevailing then, the tubeless tyres took some time perfecting. But once the virtues of lower unsprung weight, easy repairability, better ride quality and many more factors which only magnified the radial tyre advantage became apparent, the tubeless radial has gone on to capture market share in the developed lands.

            The tubeless movement is now making its advent in India getting off the ground with makers like Goodyear with its Trinuum Tyre Tech. From the cross ply to the radial to the tubeless, tyres have surely come a long way.

4.The Need for Speed - Case Study

 

The first case shows a tyre with its tread separated from its casing. Could this have been a manufacturing defect? Yes, provided the tyre was not over six years old, as in this case. The tyre was manufactured in 1994, but was sparingly used, thus the tread was not worn out but the casing deteriorated and when subjected to speeds above 130kmph, literally tore out in chunks. Thanks to radials, the owner was able to control the vehicle to a slow stop.

The second case you will notice again the tyre has suffered a tread/belt separation. This too can be attributed to a manufacturing defect. Unfortunately the owner had purchased this imported tyre from a dealer who sold him a defective tyre. This is very clear from the fact the specific markings, which give the authenticity of a tyre has been buffed off. Secondly the speed rating of the tyre was 'S' (160kmph), while the vehicle was a Mercedes, capable of being driven at speed of over 190kmph. We asked the owner to replace them with a 'V' rated tyre, for safer driving.

Here we see a tyre, which may have suffered an impact before it entered the highway. This tyre was a tubeless type but was fitted with a tube. Now the tyre must have absorbed the impact but the tube did not.As the tyre flexed, heat generated within and after the near completion of the journey the tube gave way rendering the tyre useless. The damage of the tyre and tube can be clearly seen. Moreover the nature of impact is also visible at the rim area.

The fourth case, I would like my readers to see how a nail penetration has caused this tyre to fail and by the time the vehicle could be brought to a standstill the tyre was ruined.Here again I would say that the owner has been lucky to use a radial, as although his tyre was wrecked he was able to come back with his story safely to us.
In my last case we see a tyre which has more than 60,000km logged on it. The life of the tyre was virtually over, as the tread depth had already reached its 'TWI' (Tread Wear Indictor) marking or had only 1.6mm tread depth left. Yet the owner was reluctant to replace his tyres and as luck would have it on his return after a weekend at Lonavala, the tyres developed a belt distortion. The only solution for him was to replace the entire set.

5. Wheels - The Money Spinner

            The first Grand Prix, which was held at Magny-Cours, France, in the year 1906, presented a real challenge not only for automobile manufacturers but for tyre manufacturers as well. Since the 1200km hot dusty course caused numerous punctures, it put a strain on drivers as they had to replace tyres themselves, which was a painfully laborious process. An advertisement of the time projected it to be as easy as child's play but the truth was far from it. Thus Michelin's offer of the new technical innovation of completely detachable wheels amazed spectators, specially the performance of Ferenic Sziz who won the race at an average speed of over 101kmph on a Renault engined car. The key to Sziz's victory could be attributed to the fact that he managed to change a tyre in three minutes flat with these detachable wheels. Michelin also made history when out of the 34 cars which started only 11 finished, in which the first, second, fifth, sixth and eighth were all on these wheels.

            Yet these wheels were a far cry from the wheels of today. Those days traditional carriage wheels and wire-spoke steel wheels developed for the bicycle were alternatives available for automobiles. The three types of modern wheels are of pressed steel, wire-spoke wheels and light-alloy casting wheels. The pressed wheels are light, strong, stiff and resistant to accidental damage. They require negligible maintenance and are only inferior to alloy wheels on one count; they are heavier. Over 90 per cent vehicle manufacturers use such wheels, as they are easy to produce and cheap to manufacture in large quantities. Steel wheels are made from two pressings. The inset distance and rim profile are varied to suit the car manufacturer's requirements. The flange profile, indicated by letters J, K, JJ, JK, or B in the specification, is designed to comply with the tyre bead profile.

Though I have already written about problems caused by using an incorrect flange type as well as the wrong width I repeat that it is of vital importance that correct width be maintained in relation to the tyre size as this is the factor responsible for the handling characteristics of a car. A rim too narrow in relation to the tyre width, for example, will allow the tyre to distort excessively sideways under fast cornering. On the other hand, unduly wide rims on an ordinary car tend to give rather a harsh ride because the sidewalls have not enough curvature to make them flex over road irregularities.

            The earliest type of wheels were of the wire-spoke variety. They were light yet strong as they not only had to withstand the weight of the car but also forces of acceleration, braking and cornering. Normally all wheels are subjected to extreme loads and stress even in normal road use as during cornering they have to combat combined forces of braking and acceleration. Thus all loads on the wheel are transmitted from the rim to the hub by the spokes. These spokes were made of steel as they had to be stronger in tension than in compression. Spokes individually have little resistance to bending stresses, so they had to be laced in a complex crisscross pattern, ensuring that the load fed into a wheel was evenly distributed among the adequate number of spokes, thus converting the wheel to a tensile load similar to a pulling load rather than subjecting it to a pressing or bending load.

            Assembling a wire-spoke wheel is a skilled operation, as each spoke has to be individually hooked at one end of the hub while its other end is pushed through a hole in the wheel rim, where a tapered nut also called as a nipple is screwed down pulling the spoke tight. If a spoke is too loose or too tight the rim that is relatively flimsy will distort. This labour intensified manufacture could be justified in the early days when the alternatives available were not so strong or light, but today such wheels are expensive because of their complicated construction. Such wheels are traditionally associated with vintage sport cars and racing cars, but strictly speaking have little justification today from an engineering point of view. Moreover the pierced rim of a wire wheel makes it impossible to fit tubeless tyres as they require airtight rims.

            For steering control the wheels must be of rigid construction. With a pressed steel rim the 'spoke' portion is usually of near-conical shape for extra lateral stiffness. This proved to be of great disadvantage in the earlier designs as the disc had to be liberally perforated to allow the passage of cooling air to the brake drums, thus by piercing holes in the disc weakened it. The wheel manufacturers turned this to an advantage by using a slightly more expensive technique. The holes were swaged, which means that their edges were turned smoothly inwards, thus actually increasing the strength of the wheels. Today all wheel manufacturers use swaging technique as standard on their pressed wheels.

            The third variant is light-alloy casting wheels which are generally meant to impress and essential quality and advantage is ignored. Alloys have the main advantage of being lighter than the other types of rims, but with use of a combination of aluminum and magnesium alloys have a thicker flange section, which promotes stiffness and distribute stresses over a wider area. This allows wider tyres to be fitted, which improves road-holding ability especially on corners and is one of the main reasons for their use on some sport cars. Light alloys are also good conductors of heat and thus allow heat generated by brakes and tyres to disperse quicker. They react badly to salt spray and must be checked regularly for corrosion. I shall focus on alloy wheels in future but now dwell on how wheels are mounted and problems regarding the same. The most common type of wheel mounting consists of either four or five threaded studs equally spaced in a circle around the hub flange. These studs pass through holes in the wheel, which is secured by nuts screwed on to the studs. The holes through which the studs pass are not simply pierced through but the area around each hole is pressed out to form a tapered seating which ensures a corresponding tight fit. Each wheel sits on a position which is centrally located on the hub and is called the pitch circle diameter (PCD) of the wheel. The hub diameter is known as the bore diameter.

6. THE TUBELESS REVOLUTION –

Advantages of a Tubeless Tyre over Conventional Tube Tyre

OVERDRIVE advocates the use of tubeless tyres. Why? How much importance do we place on the tyres we use in our vehicles? Where is tyre technology is to in the future? It is essential for vehicle users to be aware of the advantages of tubeless tyres compared to conventional tube tyres.

So what exactly are the advantages? The primary advantage of a tubeless tyre is in internal construction and materials used. A tubed tyre is vulnerable to friction and heat generated between the tube and the inner surface of the tube which reduces life of the tube. In a tubeless tyre the inner layer of the tyre is the tube itself. This layer is made of a material like halo-butyl/chlorobutyl which is basically resistant to heat and reduces permeation of air.

The weight of the tube inside a tyre adds to the unsprung weight affecting handling characteristics and overall performance. The lack of a tube reduces unsprung weight and improves dynamic ability. The lack of a tube also reduces rolling resistance caused by friction between the tyre and tube. The lower rolling resistance, lesser weight and the tubeless tyre's capability to uniformly retain air improve fuel efficiency

Another important advantage from a safety point of view takes care of a problem none of us have control over: punctures! Ever experienced a high-speed blowout? There have been a number of gruesome high-speed fatalities on the Mumbai-Pune expressway caused by tyre blowouts.

            At speeds in excess of 100kmph high temperatures are generated. These high temperatures expand (in some cases this tube is over-inflated too which only aggravates the situation) the tube and a sudden sharp penetration at high speed causes the tube to burst very easily. The air expelled at high pressure forces its way out of the tyre from around the rim and the tube valve hole. In some cases the pressure exerted by this escaping air is strong enough to rip open the tyre. A burst tyre causes a sudden loss in traction which is sufficient to throw the vehicle off course violently.
In a tubeless tyre penetrations into the tyre are sealed off by the rubber itself. As a result, leakage of air does not take place and if it does, it is minimal. Over-inflation can still cause grievous harm but the hazards from punctures in a tubeless tyre are greatly reduced. In case of a total loss of air inside the tyre, it is likely that the bead will collapse inside the rim-well rather than come off it.

            Other tube troubles include ballooning, open splice, spurious tubes, pinholes, tube mounting damage and finally the cost of a tube and its maintenance, all of which are avoided with tubeless tyres.

            Tubeless tyres present a very good case for themselves. They are a welcome foot forward in tyre technology that the world has accepted decades ago.?

7. Conclusion :-

            By using tubeless tyre technology which is invented by engineer Paul Weeks litch field in 1903. We can reduce friction and heat generation which is developed in conventional tyres between the tube and inner surface of the tube. By using tubeless tyre technology we can also reduce unsprung weight and improves dynamic ability. It also reduces rolling resistance cause by friction in the tube and tyre. Using this technology we can improve fuel efficiency and also reduces puncture as in tubeless tyre penetration into the tyre are sealed of the rubber is self. As a result leakage of air does not take place and if it does it is minimal. So tubeless tyre present a very good case for themselves. They are a welcome foot forward in tyre technology that the world has accepted decades ago.