There will be a difference. I'd recommend going with the 235/55-17 tire size from the DTS - the increased stiffness will not be drastic and since the overall tire diameter is very close to the original tires you will not have to worry about recalibrating your computer for a different tire size. And you can get some nice factory 17" Cadillac wheels which look awesome...If you move up to 18's and beyond you will start to notice a harsh ride IMO.