Well, I just went out to the shed and put some more air in my tires. They were at about 30 psi (max. recommended pressure for these tires is 80). I got them up to about 50-55 and they don't have the "give" now--I was afraid that if I put in much more air one might blow! I don't weigh much (105 lbs), so I probably don't need to be near the max pressure anyway. We'll see how much different it feels the next time I ride it--maybe the tire pressure really WAS the problem!