My front inner tube developed a slow puncture this week - by which I mean that it took about 24 hours to deflate. This morning I decided I would try to track it down, and inflated the inner tube and ran in through a tub of water. No sign of any tell-tale bubbles from anywhere on the tube or around the valve, so inflated it some more, and then some more, and then some more...until bang the whole darn thing exploded. Never once saw any sign of bubbles even when it was inflated to a really high pressure. I've had even slower punctures which have always shown up. Any theories? Incidentally, how puncture resistant should I expect puncture resistant tyres to be? in August I fitted some Michelin 28mm tyres that they claimed were puncture resistant and have averaged about two punctures a month since then - which is more than I managed with my ordinary old tyres.