I have a 2002 Focus 5dr and had a weird thing happening. Anytime the car is traveling between 55-65 MPH it begins to shake regardless of the gear it is in (including neutral) or the amount of gas being supplied. Any ideas?
The first thing to check are the wheels. An out of balance condition can cause this. You can even rotate the tyres so the ones on the front are put on the back and see if there is a change.
There are a lot of other possibilities and most of them come under suspension parts. Having a good alignment shop check the suspension for wear and adjustments should locate any trouble there. Note: they may well find some worn parts that when replaced do not fix the problem. There is no way to be 100% sure until those worn parts are replaced. Just remember that if the shop is honest and knowledgeable, the parts replaced did need to be replaced even if they were not causing this problem.