Off-road vehicles have had tyre auto-inflation systems for years now, because a soft tyre can provide a better grip on a rocky surface. The same functionality can also benefit mountain bikes too, which led to the development of the Adaptrac tyre inflation system for bikes.
Bikers tackling rough terrain are already able to adjust the tyre pressure in their wheels -- it just requires them to stop and get off their rides to do so. And that's no fun. So the Adaptrac system uses a special set of front and back hubs with a valve connected to a CO2 tank mounted on the frame.
A set of controls mounted on the handlebars lets the rider increase the pressure in either tyre, while a regulator valve sitting between the tank and wheels ensures they don't just instantly inflate to the point of popping. In fact, a pair of analogue gauges provides a constant reading of the actual pressure in each tyre so you don't over-inflate them. So in theory, a mountain biker could tweak the feel of their ride without ever having to break out a tyre pump, or even stop pedalling.
Of course, the whole system is completely dependent on how well the hubs are engineered. A set of rotary seals supposedly ensures there's no air leakage even while the tire is spinning, but that's something you don't want to fail when you've ridden several hours into the backcountry. As for pricing and availability, that will be announced sometime in the next couple of weeks after the design on the last prototype is finalised. [Adaptrac via Gizmag]