How long do average-quality tubes last? I patched a tube three times in a row a couple of weeks back - as soon as I inflated it it got another hole in it. Threw it out and replaced it with the spare. Today, threw the spare out in disgust as I repaired a hole then it split length-wise as soon as I pumped it up. Both tubes were about 2 years old. Size was 700 x 40 pumped to 70psi.