Hello, I just bought a SX for my daughter - no plan to mod it for her LOL but just thought I would add a comment here as I modified my own sports car rather extensively. Just trying to help here - no flame please.
A rear anti roll bar reduces lateral weight transfer (side to side roll) and therefore would help make a softly sprung car a lot more fun in the twisties. With respect to road bumps,
an anti roll bar, because it effectively stiffens the rear suspension, if anything would make the SX more choppy (not less) when there are bumps on road surface, no?
One thing I would add is that when you stiffen rear anti-roll setting and leave the front unchanged, you
reduce understeer (more oversteer) and that might be another reason (besides the reduce body roll) for the improvement in handling that people have noticed. A front wheel car likes the Forte has natural tendency to understeer, and adding oversteer is of course the counter move. Of course, more oversteer means that the rear is more likely to step out - but in a front wheel car with relative little power like this Forte, the concern of more oversteer is of course less than with say a Nissan Z.
The SX does have a stiffer ride compared to other economy cars (the same reason why it's so much fun and handles so well for an economy car in the twisties), and I attribute this to stiffer springs, larger wheel (17 versus 16), and the very low profile stock tire. There have been several posts on the Good Year tires of course, and how replacing it with Continental tire would greatly improve the stiff, choppy ride.
For those who think the
EX is too soft, yes, this anti roll bar should help reduce the body roll (no personal experience with using anti-roll bar in this car, or in any car with Torsion beam rear suspension).
For those with SX who think it is too choppy, consider replacing the Good Year with Continental; I am not sure adding this bar would help the ride. The other way to reducing stiffnes of course is to lower tire pressure - to the lowest level that's still safe. Tire preessure has significant effect on the ride stiffness of any car. Turn up the radio seems to help too LOL - so you don't concentrate so much on the noise of the road bumps.