I recently got a new pair of Continental Ultra Sport tires and MEC tubes-- cheap, I know, and maybe this is the problem, but I thought I'd ask anyway.
I put them on my bike, and immediately noticed a low point on my front tire-- I could feel the whole bike thump every revolution. I took it off and reinstalled it, and it went away.
Meanwhile, I have since changed the rear tube (I think I might have pinched it), and now the replacement has the same lull. In terms of speed and performance, there isn't too much difference. It's not rubbing on anything, there are no leaks; I just think that I'm putting the tire on wrong, somehow. These are my first 700c tires-- I have several bikes, but they are all late-70's or early 80's models, and so have 27-inch tires, and I've never had a problem like this with them.
Are there any secrets or tricks that I ought to know? I feel like all my problems with them stem from some ignorance on my part. The rims are brand new 700cs and hand-tuned by my LBS, so I know they aren't the problem.