As far as I can see, and anti-sway bar has the effect of keeping the wheels (of one axle) in the same plane (after hitting a bump or hole). It is a steel rod, which is free to rotate-each end is secured to the wheel’s suspension point. So if wheel "A: gets pushed up, the rod will force wheel “B” up by a like amount. My question; does this, in a sense, negate the effect of individual suspended wheels? Why wouldn’t a solid axle (connecting both wheels) work just as well?
For years we’ve been fed a line about the superiority of individual suspensions-but add an antisway bar, and you are cancelling (to me) most of the benefit of the individual wheel suspension.
Yeah, there’s a certain lessening of independent-ness when you add a roll bar. It also makes the effective spring rate higher, giving you a harsher ride. But the benefits of reducing body roll (thereby keeping the tires flatter on the pavement and reducing weight transfer to the outside tire) are enough that it’s worth doing.
The drawbacks of a solid axle are greater unsprung weight, gyroscopic effects from tilting the spinning wheels, and the fact that bumping one wheel affects the other. But there are still a lot of solid axles out there; it’s still a valid design solution, especially on vehicles which carry a lot of load.
I’d just like to explain that the anti-sway bars aren’t rigid, they flex like a torsion spring. It couples the wheels somewhat, but not rigidly like a solid axle.
I am mostly familiar with the effect of anti-sway bars on the early Ford Mustangs, but the use on other cars is similar.
Anti-sway bars are designed to resist body roll. They are a torsion device that twist whenever one wheel moves differently than the connecting wheel, and this resistance helps to keep the chassis and body from rolling outward from a curve, which upsets the balance and center of gravity of the vehicle. Going straight down the road, the bar moves without tension with the wheels as they move with the road. Go into a curve and the bar then provides extra tension to prevent the car from rolling and unloading the tires from the pavement.
Some older cars didn’t come with any bars, but front bars were fairly common. Usually only the more performance oriented cars also had rear bars. The 1965-1970 Mustangs all came with a small front bar and performance models came with heavier ones, with top performance cars also using a rear bar.
Adding a heavier front bar is a common modification to the old Mustangs because it is quick, easy and provides a noticable improvement in cornering ability. But since the Mustang tends to over-steer, because of auto manufacturers desire to build cars this way, and the heavy front engine design, the Mustang actually needs a rear bar. A rear bar on this car will actually help keep the front end from rolling over so much, but since they are harder to mount and hook up, the front bar usually gets the nod.
[Nitpick] Street cars understeer not oversteer. The average driver would not know what the hell to do in an oversteer condition.
Understeer is when the car want to continue in a straight line, and the steering wheel must be turned an additional amount to make the car go around the corner. The NASCAR boys call is tight or push.
Oversteer is when the rear end wants to come around and exit the corner first. Your average driver has no clue what to do if the car is sideways and headed for backward. In NASCAR this is called loose. A perfect description IMHO.
If you leave the corner and hit a tee with your front bumper you car understeered. If you hit the same tree with your rear bumper, you car oversteered.[/nitpick]
The benifits of an independant rear suspension as I understand it are that each wheel is free to follow the contours of the road without effecting the other wheel. With a solid axle, you get a see-saw effect. One wheel goes up, the other goes down. Anti-sway bars help with both types of suspension. When you hit a bump, the bar twists, and does not transmit much force to the other wheel. But when you are in a turn, the bar helps compress the suspension on both wheels, effectively stiffining the suspension and reducing body roll. If you drive a really good handling car, you can feel the suspension ‘tuck’ when you go around a corner. The car feels like it is lowering itself in a turn.
A sway bar acts like an additional spring, typically stiffer springs (higher spring rate) will improve handling but make the ride worse. Most car enthusiasts are adding swaybars to cars that did not come with them or replacing the stock sway bar with a stiffer one.
If you hit a bump or dip that affects both sides of the suspension equally a sway bar should have little effect. If you hit a bump that effects only one side of the suspension the swaybar will increase the spring rate somewhat. If you where in a situation that caused the suspension to move in opposite directions (I.E. hit a bump and hole at the same time with opposite tires) the spring rate would be effectively increased even more.
When a car leans in a turn the suspension moves in opposites directions, so a sway bar effectively increases the spring rate more when a car is cornering while having less of an effect on the spring rate in more common situations that affect ride.
Furthermore, increasing the spring rate on the rear will increase oversteer so adjusting the size of swaybars can allow for adjusting a cars handling characteristics. Typically cars come from the factory to have a tendency to understeer a lot which is safer for an average driver on the road. Some driving enthusiasts prefer less understeer and use swaybars as a way to do that.
Suspensions are very complicated and the above is just a basic outline that may not apply in all situations or vehicles.