Recently bought a 2002 DTS Deville that came with Detata DT-111 rims on it. Test drove it aorund the block and fell in love didnt need to drive out on the highway which i chould have :( The car had a slight vibration at 55-60 then would smooth out and come back around 75. Now just bought the car so it is certified preowned, warranty for 3 yrs or 100,000 miles. (28,000 currently) After noticing the vibration i brought the car back to dealer and they sadi must need balancing so i let them go ahead and when they finished they said one of the wheels couldnt be balanced, saying that the tire was bad and they could replace. I neglected to replace becasue i was getting 20" rims for the car anyways so i left it alone thinking it was the tire and after i installed 20" rims everything would be fine, but guess not> Recently installed the 20" rims from a tire dealer, all wheels were road force balanced and shake is still there. The shake is a small vibration in the steering wheel and u can also feel it in the gas pedal and the seats and sometimes. Sorry for the novel but my first question is Any Ideas? Second question: Will having 20" rims on the car hurt the warranty at all? And third question: What should i tell the dealer as they claim it was one of the tires? :(

Thanks for all help anybody can give, it is much appreciated, I will be taking the car back to dealer in a couple of weeks and would like to maybe have some ideas to mention to them, Drivers seat heater is not working and service stability keeps flashing on the screen, so it definetly needs to get in to the dealer.

Thanks Again!