I bought what I think is a decent set of rollers last winter but I can't for the life of me get good at riding them. I've tried the door frame thing and while I don't fall down, I can't seem to go for more than 30 seconds or so before I need to grab something to right myself. Pushing through the "dead" spot in my pedal stroke seems to be the problem. I can hold a line on the road, and I don't bump into anything or fall down often. What am I doing wrong? I'm using a fixed gear bike, if that makes a difference. I've tried flipping the hub to the single speed side (rather than fixed) but it didn't seem to help very much.