Have purchased this car recently, with 39000 mile on it. They had khumo tires on them. After hitting over 75 mph the steering and the floor board started vibrating . Took it back to the dealership they said that I had 2 bend rims, which they swapped it out from another car. Still the problem continued. Then they suggested it could be the tire belt. Ended up replacing the front 2 tires with Yokohama avid vs4. The vibration disappeared at 75 and only comes after 80mph .
Swapped out the rims from my friends TL type s and no vibration at any speed. Yokohama are rated at S.They should have solved this vibration problem. Or the dealership just gave me another bend rims?

 

Hmm interesting one. I had a simliar problem to yours so I balanced my tires yet still it vibrated. So I while I was doing my oil change at my mechanic I decided to ask him instead and I told him I had my tires balanced yet it still vibrates and shakes around 80 so he said probably my tires(the two in the back, one fuzion the other bridgestone) were crapped out since they were used tires I had to get when I popped two of my continentals. So I decided heck why not just change all 4 while I am at it and decided to get 4 Yokohama Avid V4S's the other day and problem solved. Alignment, Balancing, Mounted plus tires for a total of 600 bucks(expensive way to fix a problem).