why does my car vibrate in the front tires

sounds like your front wheel bearings could need replacement, If your tires are balanced and brakes are not metal to metal then I would say wheel bearings

There are several things that can contribute to wheel vibration. Tires out of balance but this is normally most experienced at 50 to 65 mph. Visually examine your tires to ensure you have no tire sidewall damage or thread damage. The noise you describe alarms me it sounds like you may have a wheel bearing that is deteriorating and at a point of failure. If you jack up the front of the car and properly support the car, spin the front wheels one at a time. Do they spin freely and concentrically without excessive weaving in and out? ( What you are looking for is less than 1/16th inch out of true other wise you have a warped tire or or bent wheel rim) Next do you hear any grinding or scrapping sounds as you rotate the wheel? Grab the wheel at top and bottom and feel for play, grab the wheel at 3 o'clock and 9 o'clock position and see if you feel excess play. At any rate get your car checked out and repaired as soon as possible or other damage will occur to other components resulting in an even more expensive repair.