Why does a steering wheel on your car shake?

If it shakes just driving at around 50 mph then the tires need balancing. If it shakes when stopping you have a warped rotor. Edit: tire balance problems are most noticeable starting at around 35 mph. Balance problems can be undetectable by 50 mph. Can also be a bad tire which will be more noticeable usually at slower speeds. Steering wheel shake normally indicates a problem with the front end while a shake felt in your feet and/or the seat will be in the rear. Shake while braking will usually be a rotor problem, however can be a bent hub or spindle and even loose steering parts. Need to take to a qualified tech for further diagnosis.