What are they exactly?Despite their banal appearance, these black rings are packed with advanced technology. They are made from a special mousse whose micro-cavities are filled with a special chemical agent that is incorporated during the cooking process, a particularly
delicate moment in the mousse's life which governs the life expectancy and quality of the end product.
The volume of this compressible, low density mousse is more than halved when the tyre is inflated. Then, should air be lost, it expands again; very slowly in the case of a slow puncture and instantaneously in case of a big cut. In the latter case, it deploys so quickly that there is no loss of 'pressure'.
Today's mousse ensures a pressure-equivalent of 1.3 bar when cold and is capable of withstanding temperatures of up to 150°C. In 2001, mousse development focused on producing an even lower density, a bigger volume and a higher equivalent pressure once deployed. The system is currently capable of resisting speed peaks of up to 200kph and can be used more than once.
But how does it work?
Phase A
The unassuming 'doughnut' of flexible foam that makes up the system is in fact a highly sophisticated piece of technology. BFGoodrich's fitters slide the mousse inside the tyre before fitting the cover to the rim.
So long as the tyre hasn't been inflated, the insert takes up all the space inside.
Phase B
When the tyre is inflated to its working pressure of approximately 2 bar, the mousse is compressed; its volume is roughly halved. For the moment, the insert is cold and therefore inactive.
Phase C
Once the stage has started, the heat generated by driving at speed transforms the physical properties of the mousse. The system is now primed and capable of withstanding the sort of dynamic loads all rally tyres must soak up. So long as everything goes according to plan 'on the outside', the system remains inactive, but ready to be deployed at the slightest alert.
Phase D
In case of air loss (because of a cut, a hole or, very often, a damaged or broken rim!), the system is instantly deployed. With air pressure no longer compressing it, the insert automatically expands to fill the inside of the tyre. Thanks to its special properties, notably its flexibility, the mousse perfectly takes over the role of the air that has escaped.
Phase E
The system has been deployed and the driver is able to continue the stage without having to stop to change the wheel. And in the majority of cases, he can carry on pushing as hard as before. It is frequent that he doesn't even realise he has punctured, especially on gravel. Fastest times set after the system has been activated are not rare. Nor are examples of drivers going on to win a rally thanks to the system!
BFGoodrich
