Tyres do not typically carry the weight of our vehicles but it is only the air inside them does. There are three basic elements which determine the load capacity of a tyre namely, the size of the air chamber formed between the tyre and wheel, the strength provided by the engineering construction of tyre to hold air pressure, and the amount of air pressure actually in the tyre.

Most flat tyres or zero pressure air  are the result of slow leaks that go unnoticed and allow the tyre's air pressure to escape over time (Fig.1). Therefore, monitoring tyre air pressure in real-time is extremely important. Fortunately, in these days we practically have such devices inbuilt in tyre, called, Tyre Pressure Monitoring System or TPMS, Fig.2. Run Flat Tyres (RFT) are typically designed passenger car tyre or light truck tyres or SUVs to run even when they are flat  or when there is zero inflation pressure. It is more of a safety issue - it's design allows you to continue driving in deflated condition to a point were you can safely get the tyre changed or repaired. To all RFT, therefore, it is was required to fit in TPMS system (Fig.2) to indicate driver that the tyre is running with low pressure or tyre is failed and is under zero pressure now.

Tyre pressure sensor (pressure transmitter) converts the physical quantity 'tyre pressure' into an industry-standard signal , that enables the driver if the tyre pressure is becoming low or the tyre has already failed during driving (Fig.2). Mandates for TPMS technology in new cars have been continued to proliferate in the 21st century in Russia, the EU, Japan, South Korea and many other Asian countries. As of November 2014, the above fitment rate stands had been to ~ 54% of passenger cars.

Tyre pressure has profound influence on vehicle safety and efficiency. Tyre-pressure monitoring (TPM) was first adopted by the European market as an optional feature for luxury passenger vehicles in the 1980s. The first passenger vehicle to adopt TPM was the Porsche 959 in 1986, using a hollow spoke wheel system. In 1996 Renault used the Michelin PAX system. In the United States, TPM was introduced by General Motors for the 1991 model year for the Corvette in conjunction with Goodyear run-flat tyres. The system uses sensors in the wheels and a driver display which can show tyre pressure at any wheel, plus warnings for both high and low pressure (Fig.2). It has been standard on Corvettes ever since.

The dynamic behavior of a pneumatic tyre is closely connected to its inflation pressure. Key factors like braking distance and lateral stability require the inflation pressures to be adjusted and kept as specified by the vehicle manufacturer. Extreme under-inflation can even lead to thermal and mechanical overload caused by overheating and subsequent, sudden destruction of the tyre itself. Additionally, fuel efficiency and tyre wear are severely affected by under-inflation. Tyres do not only leak air if punctured, they also leak air naturally (air permeability), and over a year, even a typical new, properly mounted tyre can lose from 3 to 9 psi, roughly 10% or even more of its initial pressure.

Maintaining proper tyre inflation is essential to vehicle handling, overall tyre performance, and load carrying capability. A properly inflated tyre will reduce tread movement, reduce rolling resistance, and increase water dispersion. Reduced tread movement gives the tyre a longer tread life. Reduced rolling resistance, the force required to roll a loaded tyre, results in increased fuel efficiency. Increased water dispersion decreases the possibility of hydroplaning. Both over-inflation and under-inflation can cause premature tread wear and possible tyre failure. Over-inflation can result in decreased traction and the inability to absorb road impact. Overinflated tyres will show premature wear in the centre of the tread. On the other hand, under inflation will cause sluggish tyre response, decrease fuel economy, excessive heat buildup, and tyre overload. An under inflated  tyre will show premature wear on both outside shoulders (Fig.3).

The European Union reports that an average under-inflation of ~ 6psi ,  produces an increase of fuel consumption of 2% and a decrease of tyre life of 25%. The European Union concludes that tyre under-inflation today is responsible for over 20 million liters of unnecessarily-burned fuel, dumping over 2 million tones of CO₂ into the atmosphere, and for 200 million tyres being prematurely wasted worldwide. In 2018, a field study on TPMS shows that TPMS fitment reliably prevents severe and dangerous under-inflation and hence yields the desired effects for traffic safety, fuel consumption and emissions. The above study also showed that there is no difference in effectiveness between dTPMS and iTPMS and that the TPMS reset function does not present a safety risk.

The Tyre Pressure Monitoring System (TMPS) is an electronic system in the vehicle that monitors tyre air pressure and alerts the driver when it falls dangerously low. This system involves a pressure sensor (Fig.4) fitted in tyre air filling valve. However, a given TPMS system can only work with compatible sensors in the tyres.  

TPMS notifies on vehicle dash board when vehicle’s tyre pressure is low or is going flat and this help to maintain proper tyre pressure (Fig.2). TPMS can directly or indirectly, increase vehicle safety on the road by improving your vehicle’s handling, decreasing tyre wear, reducing braking distance and bettering fuel economy. The significant advantages of TPMS are summarized as follows:

• Fuel savings: For every 10% of under-inflation on each tyre on a vehicle, a 1% reduction in fuel economy will occur. In the United States alone, the Department of Transportation estimates that under inflated tyres waste 2 billion US gallons (7,600,000 m³) of fuel each year.

• Extended tyre life: Under inflated tyres are the major cause of tyre failure and contribute to tyre disintegration, heat buildup, ply separation and sidewall/casing break downs. Further, a difference of 10 psi in pressure on a set of duals literally drags the lower pressured tyre 2.5 metres per kilometre (13 feet per mile). Moreover, running a tyre even briefly on inadequate pressure breaks down the casing and prevents the ability to retread. It is important to note that not all sudden tyre failures are caused by under-inflation. Structural damages caused, for example, by hitting sharp curbs or potholes, can also lead to sudden tyre failures, even a certain time after the damaging incident. These cannot be proactively detected by any TPMS.

• Improved safety: Under-inflated tyres lead to tread separation and tyre failure, resulting in 40,000 accidents, 33,000 injuries and over 650 deaths per year only in USA. Further, tyres properly inflated add greater stability, handling and braking efficiencies and provide greater safety for the driver, the vehicle, the loads and others on the road.

• Environmental efficiency: Under-inflated tyres, as estimated by the Department of Transportation, release over 26 billion kilograms (57.5 billion pounds) of unnecessary carbon-monoxide (CO) pollutants into the atmosphere each year in the United States alone.

A TPMS reports real-time tyre-pressure information to the driver of the vehicle, either via a gauge, a pictogram display, or a simple low-pressure warning light (Fig.2).  

TPMS can be divided into two different types – direct (dTPMS) and indirect (iTPMS). TPMS are provided both at an OEM (factory) level as well as an aftermarket solution (replacement market). TPMS is increasing consumer demand for avoiding traffic accidents, poor fuel economy, and increased tyre wear due to under-inflated tyres through early recognition of a hazardous state of the tyres.

A sensor based TPMS has a pressure monitoring sensor fixed inside the wheel and tyre  assembly(Fig.5). This is usually clamped to the wheel and constantly monitors the internal pressure of the tyre . This information is relayed to a receiving unit on the vehicle body which is connected to a processing unit in the electronics system of the vehicle. This alerts the driver to a loss in tyre pressure.

There are two different types of systems being used today: Direct TPMS and Indirect TPMS. Direct (dTPMS) uses a sensor mounted in the wheel to measure air pressure in each tyre. When air pressure drops 25% below the manufacturer’s recommended level, the sensor transmits that information to the computer system of car and triggers your dashboard indicator light (Fig.2).

Indirect (iTPMS) works with Antilock Braking System’s (ABS) wheel speed sensors. If a tyre’s pressure is low, it will roll at a different wheel speed than the other tyres. This information is detected by the computer system of car , which triggers the dashboard indicator light (Fig.2). The purpose of the TPMS is to alert you when tyre pressure is too low and could to create unsafe driving conditions. If the light is illuminated, it means your tyres could be underinflated, which can lead to undue tyre wear and possible tyre failure.

Direct TPMS

Direct TPMS (dTPMS), is a directly measuring hardware-based systems. They could be fitted in each wheel, most often on the inside of the valve (Fig.6), there is a battery-driven pressure sensor which transfers pressure information to a central control unit which reports it to the vehicle's instrument cluster or a corresponding monitor. Some units also measure and alert temperatures of the tyre as well.

These systems can identify under-inflation in any combination, be it one tyre or all, simultaneously. Although the systems vary in transmitting options, many TPMS products (both OEM and aftermarket) can display real time tyre pressures at each location monitored whether the vehicle is moving or parked. There are many different solutions, but all of them have to face the problems of exposure to hostile environments. The majority are powered by batteries which limit their useful life.  A direct TPMS sensor consists of the following main functions requiring only a few external components, that is mounted to the valve stem inside the tyre:

• Pressure sensor
• Analog-digital converter
• Microcontroller
• System controller
• Oscillator
• Radio frequency transmitter
• Low frequency receiver
• Voltage regulator (battery management)

InDirect TPMS

Indirect TPMS (iTPMS)  uses to detect the differing speed of revolution of a wheel with a reduced circumference, caused by a reduction in tyre pressure . There may be  dashboard icons for low pressure warning icon  or system failure icon (Fig.2). This system uses the ABS  or the Antilock Braking System of the vehicle to monitor the rotation speed of the individual wheels. If a deflation of a tyre occurs the resulting increase in wheel speed triggers the TPMS and advises the driver accordingly (Fig.7).

Advantages of the ABS based system include the fact that the system uses technology and equipment that is already fitted to the vehicle. Also there are no sensors fitted inside the wheel/tyre assembly which makes the tyre fitting process easier than the sensor based systems.

Dr Samir Majumdar, Rubber Consultant (India & Asia pacific), has served in leading tyre companies like JK Tyre, Kyoto Japan Tire, among others. He was technical and R&D head (Asia Pacific) in ExxonMobil. He has authored several research papers and technical books. smajumdar501234@yahoo.co.in

Kraton Corporation, a leading global producer of speciality polymers and high-value biobased products derived from by-products of pine wood pulping, has received an International Sustainability and Carbon Certification (ISCC) PLUS certification for its manufacturing facility in Niort, France.

Kraton can now supply 100 percent ISCC PLUS-certified AMS and AMS Phenolics resins using a mass balance attribution approach thanks to the certification. Kraton's dedication to promoting the biobased and circular economy is further demonstrated by the Niort facility's accreditation. Kraton is committed to lowering carbon emissions and accelerating the shift to a more sustainable future by empowering clients to include more environmentally friendly products into their supply chains.

An independent multi-stakeholder project, the International Sustainability and Carbon Certification (ISCC) is a leading certification method that guarantees accurate mass-balancing bookkeeping and reporting of renewable and recycled materials across the supply chain.

Lana Culbert, Kraton Pine Chemicals VP of Marketing, said, “Our SYLVARES™ and SYLVATRAXX™ brands feature a range of high-performance AMS and AMS Phenolics resins used in speciality adhesives and tyre applications. Our ISCC PLUS journey began in 2021 with the certification of our Sandarne, Sweden facility. Earning this certification for our Niort plant marks a significant milestone, further expanding our portfolio of sustainable solutions.”

Sumitomo Rubber Industries, Ltd. has said that it has clarified the process of rubber breakdown, a crucial element that affects tyre longevity, through joint research with Professor Gert Heinrich at Dresden University of Technology (Saxony State, Germany).

In a special session called ‘Combining Physics, Chemistry & Engineering of Rubber: A Symposium in Honor of Charles Goodyear Medalist Gert Heinrich’, which was held in honour of the Professor's medal-winning achievement, the findings were presented in an invited talk at the American Chemical Society, Rubber division, ACS 2025 Spring Technical Meeting held in Orlando, Florida, US, on 6 and 7 March. Professor Heinrich is a member of the Leibniz Institute of Polymer Research Dresden, which took part in the collaborative effort.

Tyre durability is determined by cracking processes, which result in the development of cracks and rips in a rubber substance. The endurance of rubber was previously mostly assessed using tearing tests, but there were still numerous unanswered concerns regarding the microscale structural alterations at the crack tip. This effort identified a factor that determines the start and propagation of cracks in rubber by analysing the force applied to a fracture tip using a simulation approach. In rubber, a crack tip undergoes dilatation deformation to create voids, or microvoids within the item. The fracture gets worse as the voids expand and come together. It was also discovered that the tension focused on the fracture tip is lessened when voids emerge.

The German Rubber Industry Association (Wdk) is advocating for a thorough and legally enforceable regulation of the end-of-waste status for Germany and the whole of Europe. The association is pusing for the circular economy to be strengthened for tyres.

Valuable secondary raw materials are still legally regarded as waste since there are no consistent standards for the end-of-waste status, according to Stephan Rau, Technical Director of the WDW. This restricts the market integration of sustainable recycled materials, impedes investments and creates legal uncertainties. “We call for a comprehensive and binding end-of-waste regulation for Germany and the whole of Europe to strengthen the recycling sector, facilitate investment in modern technologies, and sustainably reduce the CO₂ footprint of the rubber and tire industry,” he said.

In order to adhere to the prescribed waste hierarchy and stop illicit exports, Rau also emphasised that lawmakers must quantitatively and openly document waste tyre flows. He added that waste tyres should only be gathered by approved disposal companies and pre-sorted based on their intended use.

On the important role of mechanically recycled tyre granules and powder, Rau said, "This is an important secondary raw material that is already used in a variety of durable and safe products. A clearly defined end to its waste status must be made more economically viable. To ensure the market success of tyre granules, a risk-based approach to assessing chemical ingredients is essential. Binding limit values ​​must be assessed using a migration analysis, i.e. based on their bioavailability. Second, the use of tyre granule products must become mandatory in the construction industry and infrastructure projects. The goal is clear: Recycling must be economically viable."

Kuraray, a global speciality chemicals company and one of the largest suppliers of industrial polymers and synthetic microfibres, has received ISCC PLUS certification for its thermoplastic elastomers SEPTON and HYBRAR as well as Liquid Rubber produced at the Company’s Kashima Plant at Ibaraki Prefecture.

ISCC PLUS makes sure that certified products, such biomass and recycled raw materials, are appropriately handled throughout their supply chains, including the manufacturing process, by applying the mass-balance technique.

In the five years preceding up to its centenary in 2026, Kuraray is carrying out its medium-term management strategy, PASSION 2026. In order to achieve the long-term Kuraray Vision 2026 of being a speciality chemical company that grows sustainably by integrating new foundational platforms into its own technologies and contributing to customers, society and the planet, the company will keep growing its range of products that improve the natural and living environments.