I bought the yokohama yk580 from discount tire as well and I had the exact same problem. I even went to check my alignment and my rotors/brakes, they were fine. Finally I went to my local honda dealer (I have an 09 honda accord 2D) and had the manager of the maintenance department take a look at the vibration/shaking of my steering wheel. He did a full inspection of all of my tires and steering column and anything else he could possibly think that could cause these issues. Yet there were no definitive results. He personally said that it must be a "bad tire". So I went back to discount tire and they replaced both front tires, because we could not pinpoint which was the "bad tire". Even after all of this I still have the same issue with vibration around 55-65 mph. BUT I did recently increase the PSI in my tires from 32 to 34 (trying to improve mpg) and this seemed to calm the vibration some, which is noticeable to me and much appreciated!!