Bicycle tires lose pressure due to air molecules diffusing through the rubber sidewalls. This requires cyclists to air up their tires often due to the high operating pressures (up to 120 psi) and thin sidewalls of most bicycle tires.
I recently found this project on kickstarter.com called PumpTire.
They have almost raised $15,000 for the worlds first self-pressurizing bike tire. As I understand it the PumpTire inner tube clips into the tire to enable air to pass from the tire to the tube and you are able to change tire pressure on the fly.
You can check it out for yourself and pre-order @ PumpTire.com
Until this comes out you will still have to air up and change your tubes the old fashioned way. Or will you?
The Flybikes Cobra tube may make it a little easier for you 20 inchers out there.
The cobra tube from flybikes on Vimeo.