Run-Flat Tires and Deflation

Warning Systems

The spare tire is a heavy, and in many cases, unnecessary weight to be carried around in the vehicle. Tires are becoming more reliable and durable, but punctures can
still occur. Companies have been studying techniques for eliminating the spare tire for many years. There was an early launch of Dunlop’s Denovo with its re-inflating
insert chemistry. More recently the use of sealant technology and instant mobility systems have been demonstrated . A space saving, temporary spare is an option finding favour with some carmakers. Most of the major tire companies now have products that will run for a defined safe distance and speed when the air is lost. Self-supporting tires with heavy sidewall inserts have required compounders to formulate new recipes that are stiff enough to support the load, but also resistant to the excessive temperatures that are generated as the tire over deflects. Ultra high tensile steel cords may replace or supplement the conventional polyester or rayon carcass of run-flat car tires. The downside of this insert philosophy, which is not required for a very high percentage of the tire’s life and in most cases never at all, is that it is a heavy addition detracting from weight, rolling resistance and ride comfort. Other run-flat systems have been developed that incorporate a separate internal support ring of novel materials and designs, which prevents the tire from over distorting and hence dislodging from the rim.

The market is still reluctant to adopt these run-flat tires until there is an integral system that warns the driver of pressure loss. Many new ‘smart’ developments are
hitting the markets that monitor tire temperatures and pressures. This type of monitoring is also beneficial to fleet operators who need to measure and maintain tire
operating pressures to minimise tire wear and fuel consumption.

In order for reliable run-flat or run-on tires to be fully accepted as a means of eliminating the spare tire, a fresh look may be required into how materials and components can perform well under the rare circumstance of duress. This must be set against the fact that for most, if not all of their life, the new compounds or structures should not detract from the tire’s performance under normal operating conditions

Mathematical Modelling

In order to improve speed to market, scientists are trying to carry out as much rapid prototyping on virtual products as early as possible in the development cycle. This topic has been the subject of an earlier review . Numerous mathematical techniques are being developed using the power of modern supercomputers running finite element modelling to predict tire performance.

The main thrust of the work has been to either predict the stresses and temperature profiles within a rolling tire, or to predict the performance characteristics such as wet grip, rolling resistance, noise or handling. The road surface, tires, suspensions and vehicles are now being integrated into single models which provide the development engineers with a view of the entire vehicle’s performance long before it becomes a reality.

The coding and theory for all these models is advancing rapidly but any model requires good, accurate data and in the case of tires this is geometry and material properties. Since compounders are supplying basic data (330) on compound properties to drive these models, new modes, even multiple modes of deformation are required to produce the necessary material parameters.
New test rigs and methods are being devised to feed the models with the appropriate data. How long will it be before the desired tire performance properties from these models are fed back to the compounder, who will have to produce a compound, or even to raw material suppliers who will have to develop an ingredient with a specific set of properties?


Compounders are also using modern analytical techniques like neural networks and fuzzy logic for compound property optimisation. Scientists can model polymers and other ingredients at a molecular level to study the effects of changing the molecular building blocks or the way in which the polymer chains crosslink. Mixing and extrusion processes have been modelled . Modelling final material or even tire properties from raw ingredient data must be a logical progression to this advance in performance prediction.