Originally Posted by alcheng

that is if you stiffen the rear suspension too much with either sway bar or the spring/coilover.

Remember the stiffer the rear the less of the traction it will have. Too soft, it will induce understeer.

Sway bar will decrease body-roll, however, it will still increase the stiffness of the suspension, mainly on the inertial-response before the sway starts compressing the suspension on the other side.

Some people just blindly stiffen everything and thought it is the way to go, and ends up lose all the traction front and back thus the car is like skating on the road.

Especially on a RWD car, the rear end is very sensitive, if you mod the rear end in a wrong way could induce over-steer on both turn-in and exit.

That's why, on street/DD, it's not a must to change the rear unless it's necessary.