It was three years ago that we first heard about inventor Benjamin Krempel's PumpTire – it was a prototype bicycle tire that used wheel motion to keep itself inflated. While it was an interesting idea, it would require users to give up their existing tires, plus the peristaltic pumping mechanism would be compromised once the tread wore away. Well, he has now come up what sounds like a better alternative: the PumpTube.

Here's the general idea regarding how it works …

Air is drawn in from the atmosphere through a one-way valve, which sits in the valve stem. Instead of going directly into the inner tube, however, the air goes into one end of the tube-like pumping mechanism, which runs along the outside perimeter of the main inner tube. As the tire rolls against the ground, the pumping mechanism is compressed, forcing air into the inner tube. The resulting absence of air in the pumping mechanism creates a vacuum effect, drawing more air in through the valve.

That said, if the inner tube is already at its desired pressure (which can be set on a dial on the valve stem), no additional air is pulled in.

A cut-away diagram of the system, in which the beige element represents the pumping mechanism PumpTire

The idea behind the technology is that riders will no longer need to pump up their tires in order to compensate for seepage or pinhole leaks. While larger punctures may not have as much of an effect as they would otherwise, they'll still ultimately need to be patched.

Plans call for the first PumpTubes to be compatible with third-party 700c and 26-inch tires, and to retail for US$30 to $55 per unit. Krempel tells us that he hopes to launch a Kickstarter campaign sometime next year, once the design has been perfected.

Source: PumpTire