 2001-focus vibration
I have a 2001 focus. I put new tires on it about a yr ago. After 7 months the steering wheel started to vibrate and wiggle horribly. I rotated all the tires and that seemed to fix the problem..Now about 5 months later, its started to vibrate again..When I'm going around 65-70 the car starts to vibrate, not the steering wheel, or when I engage the brakes...It also doesnt pull to the left or right. The vibration is felt in the steering wheel, and the gas pedal, but again the steering wheel does not shake. The vibration goes away when I go around turns and when I increase the speed from 70 to 75/80. What could possibly be the culprit??? Anyone ever experience this situation? Please advise if you have a possible solution...thanks | 
