Originally Posted By: Shannow
You have to look at how the suspension is supposed to work in the first instance.
When I started playing with cars in the 80s, they were late 65s, early 70s sedans with IFS, live rear axles, and no bars. Sway bars always made them better...playing bar diameters was an easy way of moving over/understeer.
Could be done with clever springs.
As I moved into late 70s stuff, they came with bars, which left me a choice of increasing spring rates, or increasing bar rates...My preference was softer springs and more bar (one of my Toranas, I kept the stock spring rates, and went from 18mm front to 26mm, 12mm rear to 22...was wicked on corrugated dirt roads, but turned so well)
Bars, as has been mentioned make for poor articulation in trucks...in the last mentioned Torana, I would get crossed up and wheel spinning in friend's driveways when they were that artistic looking steep spiral down to a change of direction, slight up, and onto a flat parking surface...the bar would unload the inside wheel.
Which is why light trucks don't have them...they need articulation, and need both wheels loaded to provide traction.
But, and there's always a but, when you look at a cement truck, they are narrow wheelbase, very very high CoG...and have a massive rear anti roll bar, to stop the lean and sway.
My Nissna has a coathanger front bar, and big leaf springs (rated to a tonne carry), and is very predictable. I don't think I want more bar, nor want to add one to the back.
If I permanently affixed a rooftop tent, and other high loads, I would be tempted to emulate the cement truck and add bar for the highway, but would lose articulation to the camping areas.
I'll second this post and highlight two important parts:
1. Stability: stiffening the rear by adding a sway bar will effectively transfer overall grip to the front of the vehicle, making it more prone to oversteer, which, in the manufacturer's mind (and probably when it comes to a lot of drivers) provides for an unacceptable risk of unpredictable oversteer compared to stock understeer.
It does make the car feel better and, if done right for an application, can make the car feel more neutral, if that what you're going for, or tail-happy, if you're after that instead.
2. Independent suspension: a sway bar ties the left and right side together, so the on inclines at an angle or while going through ruts, etc., you're more likely to lift a wheel and possibly lose all traction.