Thanks for all the replies. I didn't get a chance to mark the tire and install it 180 degrees from the rim, but I will do that when I get a chance (damn finals...).

I'm pretty sure it's not pinch flats. I do check them for pinching with the tire but never find anything.

I do not think there is a rim "indention" that keeps the tires in place. It looks like it just goes smoothly straight up. These wheels *are* pretty old, being from the 80's, and perhaps this is the problem. But I'd still like to have at least 80 psi since anything less than that (and even that) seems to be kind of flat and causes lots of resistance...

I actually just realized something that may have caused the problem. Someone mentioned that perhaps the wheel is too small. I actually just tightened some of my spokes because some of them were hideously loose (without truing or anything, I just tighened the loosest ones and kept going around until they sounded about the same pitch), and this may have shrank my wheel size--not dramatically, but maybe enough to cause the wheel to be too small for the tire? I may have *overtightened* them, which I doubt, but it is possible.

My tire size is 27x1 1/4" and so is the wheel (I think--this is what size tire WAS on the wheel). They seem to fit really well too.

Specialized says that I can send the tire back and they can issue me a replacement. At least that's an option over Christmas break when I won't be riding my bike for 2 weeks anyway (going back home from college). But I'm not sure if its worth the shipping to them for like $5 for a $13 tire.

I'll do that trick and try to find out if its the tire or the rim. Thanks guys!

Adam