Sometimes the side walls of the tires break down and would cause a vibration. If this is so you may notice a bulge on the side of the tire. Also, you should have your tie rods and ball joints checked for wear. If you are a two foot driver (one foot on the accelerator and one on the break) your wheel disc may be warped from excessive breaking. If your struts are worn ( which is common in Japanese cars) your wheel will lift of the road causing it to "bounce". this would feel like a vibration at high speeds. Then again I have had my tires balanced and they didn't do it correctly.