<shrug> Take the advice I gave jan... get on ya bike and start pedalling around the bike shops to see what they sell 'em for. Don't use them myself. Prefer the tyre pump, although the right shoulder I broke in September was complaining a bit the other morning and gain on Saturday afternoon. And the thought did cross my mind. I'd go for helium gas, though -- reduce the weight of the tyre/tube/wheel...

About time for some new tyres, I guess.