i just purchased a set of 35c cyclocross tires to use on my fixie/beater bike in the lovely winter weather we've just begun to have here in new england, and i had a question about the tube size. i'm running normal 700x25c tires on the bike now, and the tubes are sized at 700x19-26c, i believe. now, i'm assuming that i could install the 35c tires with the same tubes and they'd just expand, but i'm just wondering, is that going to present a problem when i switch back to the 25c tires? are the tubes going to stretch out to the point where they'll be too big for the 25c's? i know i could just go out and get different tubes, too, but i'm just wondering if i could avoid doing that if i need to.