I am looking for a good brand of tubes for a 700X38c tire on a hybrid. I bought some Pyramids, but am less than impressed. I want something relatively puncture resistant, with good pressure retention. The pyramid tubes I bought lost 20 pounds of pressure overnight. Iremoved the first one, checked the tire for sharp nasties, put another tube in, and the same thing happened. I have to assume that they are low quality tubes. The local LBS would not answer my question about better quality tubes. Iwanted to know what was the best, they kept telling me which one of the ones they sell was the best. (Subtle difference, I know). Anybody researched this?