At idle, my car runs smooth, but while i'm driving, the ride tends to be more shakey. I can feel the shakier ride more as i'm slowing down to a stop, but as soon as i'm at a complete stop, i'm at a smooth idle. I started noticing this after i replaced my front tires with some used tires(for the mean while) and am not too sure if the wheels were balanced.
Any suggestions?

Tom

I think you answered your own question,most likely broken belts in the tire.