This is know as "cupping", how to check for it just run your hand along face of tire you can actually feel it. If your tire is flat it gives you a better idea...it will be like small waves that is cupping. "what causes cupping? " I usually is an "alignment" problem. If in doubt, and your car is wobbling at the same speed, give us a call, we'll inspect your tires for free.
Your tire will have large and small cracks and pimple like(bulging) look to it. We live in weather that is very harsh on our tires, so we end up with larger then usual "potholes". Continually hitting these will cause the "pimple" like appearance in your "tire". When you have these cracks and/or bulging you need to replace this tire, it will become flat eventually
Problem 1: Look at your tire is it worn down the middle? Cause: Your tire was overinflated, only the center ring will have contact to road, when that happens your traction suffered. Look inside the door placard or check your owner's manual to know the correct tire pressure. Before you start driving and when it is cold outside, check the pressure. If in checking the pressure is correct, it may indicate that the wheel and tires are not properly matched.