TYRE DEFLATION

When a fully inflated car tyre is allowed to deflate, the air streaming through the nozzle is cold to the touch. The pressure of the air within the tyre is fairly high, so opening the tyre valve allows it to leave the tyre rapidly - the air movement may even cause a breeze. We could feel a jet of cold air on our face if we were close enough. As it leaves the tyre, this jet of air pushes away atmospheric air, which requires an effort. We say that work is performed. (It is a form of pressure-volume work, and will be discussed in more depth later, in Section 3.2.)... 

We see how the spontaneous movement of gas always occurs from high pressure to low pressure, and also explains why a balloon will deflate or pop on its own, but work is needed to blow up the balloon or inflate a bicycle tyre (i.e. inflating a tyre is not spontaneous). 

It should be clear from Equation (4.39) that gas movement in the opposite direction, from low pressure (/>(finai)) to high (/Amman) would cause AG to be positive, thereby explaining why the process of gas going from low pressure to high never occurs naturally. Stated another way, compression can only occur if energy is put into the system so, compression involves work, which explains why pumping up a car tyre is difficult, yet the tyre will deflate of its own accord if punctured. 

Why does deflating the tyres on a car improve its road-holding on ice ... 

In a similar way, if we deflate slightly the tyres on a car, we see the tyre bulge a little, causing it to sag , with more of the tyre in contact with the road surface. So, although the weight of the car does not alter, deflating the tyre increases the area over which its weight (i.e. force) is exerted, with the result that we proportionately decrease the pressure. 

Cascade failures a single failure may overload the remaining channels, thereby increasing the probability of their failure. Or, an initial minor failure (e.g. a deflated tyre) causes a cascade of events (e.g. Concorde). 

---