Unfortunately, you need to be the judge whether you need a rear sway bar. If you have too much body roll, or the front end always wants to slide out on the curves or corners, then you could add a rear sway bar. There are many factors to take into account when setting up the suspension, whether its for racing or just having fun, the rule of the thumb is the stiffest axle will be the one to slide out first, what this means if the rear becomes the stiffest axle then it will slide out first in the corners. Like I said there are many factors, like center of gravity, spring stiffness, geometry of the steering and front end components, stiffness of the sway bars. One thing you don't want is too much body roll where the suspension bottoms out, this is a bad condition, but you want the softest suspension where it doesn't bottom out. I hope you are understanding what I am saying. I'm not an expert, but I have raced at speed in my 67 mustang conv. My 2004 Mustang convertible acts like it is glued to the road and to my surprise it doesn't have a rear sway bar, only a big one up front. It's all about getting it set up right for your vehicle. n My 2 cts. Good Luck.