Does a Rear sway bar really help?

[VQboy]

Just had a question regarding whether a rear sway bar really improves handling in a car such as the I30 that uses a multilink beam suspension in the rear. Would the fact that the car uses a beam-type suspension, where the two rear wheels are inherently linked together, minimize the need for a rear sway bar? I suppose I'm asking this question because I'm curious to know whether I will notice a dramatic improvement in handling if I were to install a rear sway bar on my 1999 I30. I've read many positive comments regarding improved handling once a RSB was installed.

Your thoughts on this subject are much appreciated. Thanks!

[greg_atlanta]

Would help to see pictures showing where it mounts. It's impact depends on how heavy it is.

I have sway bar on '92 Q45 and it does make a difference, but not a huge difference.

Best to spend money on new, stiffer shocks and sticky tires first.

[911/Q45]

I put rear sway bars on several cars that had solid rear axles and it made a big difference on them, so I'd bet on a major effect on your I30.

[Q45tech]

You have to look at it like this: how does removing 120 pounds from an overloaded tire improve handling.Say a 3500 pound car has 60/40 weight distribution, each rear tire has a 700 pounds static load. Because the rear has light springs say 100 pounds per inch of body roll and the center of rear gravity is high...........the body roll shows that 300 pounds is being transferred side to side in turns.The sway bar forces the unloaded tire to take more load. So the sway decreases.

On a car with 4 wheels the situation where all 4 tires see equal weight in turning produces the best handling.

Sway bars can't compensate for bad weight distrubution but they can make the car feel like they can at least up to a bar stiffness equal to a maximum of 50% of whatever springs they try to control.

Race cars don't sway, street car must, to be tolerable on rough streets.

[s13sr20chris]

forgive my ignorance. i know a rsb helps even with a solid beam in the rear, but i dont see how you can get any stiffer than a solid beam axle. am i correct that one rear wheel can not move up or down independently of the other?

[Q45tech]

The body sways on the springs, thats what they do hold the body up and push the tires down against the road with a force equal to the weight on the springs.

Sure each tire can move up/down qausi-independently by introducing angle in the tire carcass.................ever tried to jack up one tire.

[s13sr20chris]

yes i see, i was forgetting the body. my thoughts were entirely related to the suspension. i was visualizing the whole axle moving and failing to realize the body movement being independent. heh, even on a dependent suspension you have and independent body. you would think i could figure that one out on my own. well thanks again q.

[Carter]

A rear anti-roll bar (more accurately describes what it does) helps reduce understeer. That is, the car turns better with slightly less steering input. After installing a rear bar, the driver will notice this, thus the "improved handling". Going too stiff makes the car "twitchy" and it tries to swap ends at turn-in, thus the need for a balanced car. On the track, we start the weekend with the adjustable rear bar on full soft. Each session, we stiffen it one setting until the car turns-in nicely but is still fairly stable. This balanced handling makes the car easier to drive quickly and brings down lap times.

Installing stiffer rear springs (obviously more involved) and even raising rear tire pressures, to a point, can give the same effect.

Stiffening the front bar, springs, and tires increases understeer. Stable and easy to recover, but slow.

Easy to remember, "the stiffer end of the car loses traction first." With a balanced car, the car turns-in nicely, and the driver can get on the throttle early at corner exit. With an oversteering car, the driver is fighting the car to keep it from spinning and has to wait to get it stable, to pick up the throttle. With an understeering car, the front end washes out and the car won't turn. The driver has to slow down to get the car to turn, he waits to get through the corner, and then gets on the throttle.

Carter

[NewJerseyDevil]

A rear anti-roll bar (more accurately describes what it does) helps reduce understeer. That is, the car turns better with slightly less steering input. After installing a rear bar, the driver will notice this, thus the "improved handling". Going too stiff makes the car "twitchy" and it tries to swap ends at turn-in, thus the need for a balanced car. On the track, we start the weekend with the adjustable rear bar on full soft. Each session, we stiffen it one setting until the car turns-in nicely but is still fairly stable. This balanced handling makes the car easier to drive quickly and brings down lap times.

Installing stiffer rear springs (obviously more involved) and even raising rear tire pressures, to a point, can give the same effect.

Stiffening the front bar, springs, and tires increases understeer. Stable and easy to recover, but slow.

Easy to remember, "the stiffer end of the car loses traction first." With a balanced car, the car turns-in nicely, and the driver can get on the throttle early at corner exit. With an oversteering car, the driver is fighting the car to keep it from spinning and has to wait to get it stable, to pick up the throttle. With an understeering car, the front end washes out and the car won't turn. The driver has to slow down to get the car to turn, he waits to get through the corner, and then gets on the throttle.

Carter

good info.

[Q45tech]

Remember factory cars have a tremendous amount of UNDERSTEER to be safe in rain with average untrained drivers in emergencies.

Difficult to find rear bars stiff enough [when actually mounted on the vehicle] to even get to Neutral steer, much less oversteer unless you degrade traction by trying to accelerate in rain or on snow or ice.

That is the great challenge to select a rear sway bar that is still safe for untrained drivers who do foolish things.