Originally Posted by engifineer

a strut bar does practically nothing for body roll, that is not its real purpse. When the chasis flexes (especially on a macpherson strut/unibody design) the strut towers move in relation to one another. This means that your camber is affected since the tower moving changes the camber. This, in turn, effects the traction component since your tires are no longer aligned properly with the pavement. Tying them together with a strut bar reduces this effect, thus helping out front end handling.

On the tC, the strut towers are practically part of the firewall, so they are tied together a little more than some cars stock. Now, before someone goes on about how sheet metal is so weak and provides little support (like I have heard before), we are talking tensil strength more than bending strength, so there is some support there in this area. However, a strut bar will help even more.

So the effects are probably not gargantuan for the tC, but they are there when you start pushing the car.

So in the area of alignment control in turns, the strut bar is helping. In the area of body roll, you are looking more at a sway bar. That is the main purpose of sway bars, to remove some of the independence in the suspension to prevent body roll. Too stiff will get rid of a HUGE amount of body roll, but will also make the car start to handle worse over bumpy surfaces.