ok i just recently bought a 350z touring...and i never drove it on the hwy during the test drive because it was raining like crazzy..but now that its all dried up i noticed when going 50+mph the rear end feels like im on a dirt road or like the tires have to much air...air press is at 35psi like specs says...someone said that it could be because the tires are cheep tires..they are brand new i never heard of them before?? any help would be awesome..they checked the rear end at the dealer and theres also nothing wrong there