(Video Link)
Benjamin Krempel founded a company called PumpTire, which is marketing a rather unique bicycle tire. It has a partially open tube on the outer circumference. As the wheel turns, it opens and closes the tube, which draws air from the outside and pumps it into the interior of the tire. When the tire reaches maximum pressure, it shuts off. In a test ride featured in the video, the tire inflated from 22 to 52 psi after three and a half minutes of riding. Link -via DVICE
1) rubber has to be thin to flex but is in the #1 spot for wear - tire will wear out fast and can't be repaired
2) increases rolling resistance which is biker's #1 worst enemy
3) adds weight to wheel, which is really bad for stability and efficiency
4) most of the time a tire just goes flat and rider still needs a pump. this will only help when there is a slow leak in the middle of a ride - a rare occasion
Seems like this will work best for large, low pressure tires.