Stearing Wheel shaking

Usually it is an imbalance in a front tire that causes a steering wheel to shake particularly at 55 to 60 mph. When a rear tire is badly out of balance you usually feel it in the seat of your pants. For it to be felt in the steering wheel the tire must be really bad. If you like jack up the car and spin that wheel to see if it runs true and closely inspect the tire thread and sidewall for wear and damage, but safe]est to get it checked by a professional to see how many tires you should replace.