Questions:
1) Did you buy this car new?
2) If not do you know if the car has been lowered?
3) If it has been lowered, was the shocks changed when the springs?
4) Have you shocks been checked?
Your tire problem sounds suspicious to me. You should not be having that problem. 235X40X17 is a standard option tire for that year, series BMW
You did not say which 3 series you have so checked at Tire Rack on optional 17" sizes.
http://www.tirerack.com/index.jsp
Andre