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Got RD swaybars installed last week on my 2001 325ci. Very nice improvement on reducing body roll I notice that I'm not pushed to one side of the seat or the other on high speed turns.
One unexpected surprise was the vast improvement in driving with heavy cross winds. My car was easily upset while driving with cross winds over 20 mph. It now feels much more planted. While driving home after the install on the thruway at speeds about 80 mph and 25 mph crosswinds I could easily steer with just one hand.
 

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I understand the performance improvements of sways but how do they work? Are they for cars with independant suspension only? Why is it that the thicker they are the better?

Anything about them that would account for that cross-winds benefit you are talking about?
 

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Swaybars keep the shock towers from leaning over too much. The thinner they are, the more they flex and the mor ethey let the towers lean.
The thicker ones help improve wind resistance because they keep the car from leaning, or getting tossed about in the wind. (The wind moves the car atop its suspension.)
 

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Well... Rob estimates about a month to xi swaybar goodness. I am REALLY looking forward to this.
 

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Nick325xiT 5spd said:
Swaybars keep the shock towers from leaning over too much. The thinner they are, the more they flex and the mor ethey let the towers lean.
The thicker ones help improve wind resistance because they keep the car from leaning, or getting tossed about in the wind. (The wind moves the car atop its suspension.)
Thanks! Great explanation.
 

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You're welcome. I really learned about what wonderful things they do for handling in my old E320 4Matic. The rear sway BROKE. Every time I hit a corner at almost any speed, the car was heeled WAY over. Yes, it sucked on the highway, too. :p If you think Benzes underteer badly, wait'll you try one with no rear sway. :D
 

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Sorry. Nick, I think that's a pretty bad explaination of what they do, even in 1 sentence. The shock towers are part of the unit body, so they don't 'lean'. What's happening is that when a car is turning, its centrifugal force causes the body to want to keep moving in a straight line when the tires are pointing somewhere else, and causes the body to 'roll' onto its outer suspension. A swaybar (or antiroll bar) forces the left and right sides of the suspension to be connected to the body in a way that the outer suspension can't compress without the inner doing the same, and neither can go very far opposite from one another since they're now also connected to the body.

Take a look at this: Grassroots Motorsports
 

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Ah, oops. Misconception on my part.
 

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Robert said:
Centripetal force is actually the correct term here. Sorry, I don't mean to nit pick but someone may be taking finals and get that wrong on a test or something.
Actually, I tried to decide whether it was centripital or centrifugal, and I believe centripital force is the force holding the car in the circle (i.e. tire traction) the opposing tangential force pulling it out is centrifugal.

OTOH its been a number of years since I took physics... :dunno:
 

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Kaz said:


Actually, I tried to decide whether it was centripital or centrifugal, and I believe centripital force is the force holding the car in the circle (i.e. tire traction) the opposing tangential force pulling it out is centrifugal.

OTOH its been a number of years since I took physics... :dunno:
There is NO such thing as a centrifugal force. Centripital force is what makes a car want to go straight, and what laymen refer to as centrifugal force is centripital force but with a negative vector, because as we all should know, for every force/action there is an equal opposite reaction.

Guess what my major was in college. :(
 

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Let's put it another way.

As the force of the turn (I don't care if it's centrifugal or centripedal, although I do know that Hack is correct) causes the body of the car to lean, think about what happens:

On the outside of the turn, the body tries to move DOWN (closer to the tires). On the inside of the turn, the body tries to move UP (away from the tires). It doesn't matter if the suspension is independent or solid-axle; it's the springs that are compressing on the outside wheels that allows this to happen. The wheels stay "flat" (because they stay on the ground, unless you're driving like Hack, but that's another story....), while the body leans.

Swaybars try to keep the body aligned with the ground and the wheels. Swaybars are a giant, U-shaped spring. One end of the U attaches at an inside wheel, the other end attaches at the outside wheel. The middle of the U is attached to the body. Imagine that the "U" is lying flat, parallel to the ground, with the arms pointing forward and the curve pointing toward the trunk.

As one side of the car tries to move down toward the wheel, that arm of the U-spring tries to resist, pushing the body back up. At the same time, the other side of the body is trying to move up, but that arm of the U-spring is pushing down, trying to keep the body down. The two arms always try to push in opposite directions.

In the middle, where the U connects to the body, the mounting points allow the whole contraption to swivel. That way, the swaybar has minimal effect on the way that the suspension handles bumps. Hit a speedbump, and both wheels go up (closer to the body), and the swaybar simply pivots on its center connection. The regular suspension springs do all the work soaking up the jolt.

On rough and uneven surfaces,where the tires are trying to bounce in all sorts of directions with the independent suspension, the swaybar has the effect of "semi-tying" the wheels together. To put it another way, the swaybar tries to limit the amount of independence the wheels have. So a somwhat harsher ride can result, under those conditions.
 
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