The stock bar on sedans are 16mm and on coupes it's 17mm. I have a sedan and I upgraded on it a barely lowered car and I noticed a big difference if you do some hard driving. I mean the progress bar is an even bigger difference but to be honest, if you don't take turns insanely fast or drive fast, you won't really require the big upgrade. Rear sway bars only makes a difference on turns and you won't feel it driving on a straight road.