Tires: Car vibrations, cv joints, mitsubishi mirage

Question
Hi!
  This is my problem: At low speeds my car has a high amplitude low frequency vibration,which stops at about 30 mph and it has nothing until 55 or 60 mph, when the vibrations are high frequency, medium amplitude. However i am very concerned about the material fatigue and other problems that might develop. My car is a 1993, Mitsubishi Mirage. Thank you very much

Answer
There are a number of things that could cause this:

Tires out of balance - not likely as this should only show up at higher speeds

Tire and / or wheel out of round - probably

CV joints - There might be some noise associated with this as well as the noise might change tone when the steering wheel is turned.

Engine surge - not likely and would be more engine speed related rather than road speed.

Hope this helps.