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.
What make the steering wheel shake is the tires that need wheel balance.
Brake rotors are warped.
Your power steering pump and or steering box may be about to give out on you.
A shake in the steering wheel or car itself which occurs and/or increases as vehicle speed increases.
If your steering wheel is shaking you probabley messed you wheels or axel up
Not the steering wheel shake itself, however what is causing the steering wheel shake, can certainly be extremely dangerous and potentially cause you to lose control of the vehicle. **GET IT CHECKED OUT BEFORE THAT HAPPENS**
have front suspension checked
Wheel balance
If other things vibrate as well as the steering wheel you might have a damaged motor/transmission mount.
i would really like to know myself
Get the tyres checked for balance, and bulges in the side wall.
You may have a bent wheel, defective tire where a steel belt has shifted or broken, worn steering parts, and possibly a defective wheel bearing.