I can't figure out what I'm doing wrong. I bought three new tubes two weeks ago, Presta valves, sized 18c-25c, for use with my 23c Ultra Gatorskins. I pumped them up to about 100psi at night, and by the next day (no riding) my rear wheel was flat. I tried replacing the rear tube, and pumped it up to 100psi again.
I didn't ride this bike for about a week and a half after that. Then, before I took it out for another ride, I discovered both tires were down to 40psi. Pumped them up again, and they seemed to hold air... but the next morning, the front was down to 40psi again, and the rear was completely flat.
How can these tubes be giving up on me so quickly? Any ideas?