How sway bars work, and why people use them.

Here's how a sway bar works.

Normally, without a sway bar when the car corners the weight of the chassis shifts toward the outside of the turn compressing the springs on that side. The springs on the inside generally extend a little, or do nothing. Relatively to the chassis itself, it appears that the outside suspension compresses and the inside doesn't.

A sway bar couples the suspensions on each side to each other, *AND* relative to the chassis. If you could put the car up on a lift and actually compress the suspension on one side by hand, then a sway bar makes the compression of one side also try to compress the suspension on the other. Ok.. it's still not really obvious why that's useful so I'll say the same thing a different way.

A sway bar effectively increases the spring rate on whichever side is compressed the MOST. If the sway bar were absolutely solid with no twist so there's a 100% coupling between each side then an attempt to compress one spring actually becomes an attempt to compress both springs. It doubles the spring rate. If the bar has some twist, then it may only increase the spring rate by say 50% on whichever side is compressed the most.

So you're driving down the road and you go over a bump that goes across the entire lane. The sway bar does nothing. Both sides compress normally. You go around a corner and the chassis starts to lean and compress the outside
suspension and now it's as though you have a bigger spring out there, so the car remains more level. That's the good part. Here's the bad part. You hit a bump with only one side, and it behaves the same way, as though you have a stiffer spring, so you feel uneven bumps more. You feel it crossing anything
diagonally as well, such as coming into or out of a parking lot or driveway curb.

That's all the simple "How does a sway bar work?" part.
The real tricky one is.. "What does a sway bar do?"

1. We know it keeps the car more level. So what? Limiting the lean of
the body is good because it means that when you take a quick set into
a turn, that the body isn't still moving sideways after the tires at their
limits. Otherwise you turn in quickly, the tires grip, then the body finally finishes leaning, when it stops, the tires loose grip. This is especially noticable in most cars in the slalom where you lean one way then the other and so forth.

2. It limits camber changes. The camber is the angle that the tire leans in or out at the top relative to the chassis of the car. The camber directly impacts the angle at which the tirecross section meets the road and thus controls lateral grip. As the suspension compresses the camber angle generally changes relative to the chassis. With a normal Macpherson strut that hasn't been lowered, the camber goes from positive to more negative as the lower A arm swings out straight, and then back to positive as it swings up. That swing up into positive camber is BAD. At that point the chassis is already leaned over so the tire may be starting to roll onto its sidewall. Changing the camber even more positive just just nasty. A big sway bar will prevent the body roll in the first place, and prevent the suspension compression on the outside which causes the positive camber change relative to the chassis.

3. Transfer lateral grip from one end of the car to the other.
This one is a real trick to understand, but racers exploit this EVERY time they go on the track. Their spring rates are often so high, the cars so low, and their suspension travel so little, that the whole camber and body lean problem is alreadya non-issue. The car doesn't lean much with 500 lb springs. They use their bars to change the balance of the car. Here's the simple rules first.
A big bar on the front, increases rear lateral and motive traction.
A big bar on the rear, increases front lateral and motive traction.
The applications. If the car is understeering, decrease front bar size, or increase rear bar size. This increases front lateral grip and decreases rear lateral grip giving the car a more neutral to oversteer feel. Reverse the process for too much oversteer. I mentioned motive grip. That's the neat one. Let's say your RWD car is handling ok, but everytime you get into a corner hard and get on the gas the rear inside tire breaks loose and spins. You can't accelerate out of the turn. You can go around the turn quite quickly, but you can't accelerate out, and the guy with traction hooks up and passes you halfway down the next straight because he came out of the turn going 3-4mph faster. The reason you're losing the traction at the inside rear, is usually because the rear bar is too big. As the rear outside suspension compresses, it's actually causing the rear inside suspension to compress as well (because the bar couples the sides.. remember where we started), and that decreases the weight on the rear inside tire. First thing. Decrease size of rear bar. That decouples the sides a bit, let's the inside tire press down on the road more and thus not spin when you're on the gas.

Here's where it gets really tricky.
If decreasing the size of the rear bar doesn't help enough the next thing you do is increase the size of the front bar. When the outside front compresses in a corner, it causes the inside front to compress and may actually lift that tire completely off the ground. The car is now sitting on 3 tires and guess where the weight that was on the inside front goes? Outside front? Some of it. The rest goes to the inside rear where we need more grip. The total weight of the car hasn't changed. It's just been redistributed, and a sway bar at one end, actually transfered weight to the other end of the car. Here it is in action on a RWD car.



See the inside front tire off the ground. That translates into more motive grip
at the rear, and thus more acceleration, and believe me, that car rockets
out of corners.

All of this trickery applies to a FWD car too, and since the front tires share all of the motive AND most of lateral traction (because most of the weight is in front), all the things that happen with big bars at either end are even more extreme. A big front bar stabilizes the body lean more but also creates a lot more understeer, and may make the inside front tire spin madly under power in a corner. A big rear bar can't give you back much lateral grip up front, but it can give you back some motive traction. Basically lettting you
accelerate out of the turn, even when the front end is sliding pretty badly.

Here's a big rear bar in action on a FWD car.



So that's it. How they work, and what they do.

Here is a couple of shots with too much rear bar and not enough front spring...



(borrowed from an earlier post)

 

thanks for the info!

 

http://www.houseofthud.com/cartech/swaybars.htm

Came from this site compliments of Kennedy

 

I tried to get Kennedy to start this thread about a month ago.....PM'd him and mentioned it in a thread....so I did it myself. Its good info we should have on here. Although on this houseofthud site...there was a few missing pics that my autocross buddies helped to fill out....other than that...this is straight up lifted information like a mutha!

 

Good idea Mike, sorry I didn't acknowledge your suggestion sooner.

Thanks for taking the time to do this... I was too lazy, been distracted with other things...

Hopefully this will exaplain once and for all the age old question of "should I upgrade my front sway bar... to which I reply vehemently... NO.

 

Kennedy and MB

What do you guys think of upgrading the sway bar bushings to PolyUrethane
a little extra stiffness without the break your back big bars.
It worked on my old chevy truck but since you guys autocross the TL...

Has anyone seen Poly end links for our cars?
I am a gen 2 car

 

I think poly is excellent, but it does require you to keep it greased a bit to prevent squeaking.

I have 22mm Comptech RSB with Energy Suspensions poly bushings (greasable). I have the ES 24mm poly bushing to go with the Progress rear bar, when I upgrade.

I also have a set of 27mm plain bushing on my desk that I plan to try and make fit in the front.

Rubber, over time, flexes and degrades, where the poly tends to stay firm and last longer. Poly is great at "making the bar work" as designed.

 

Good info

 

definately!

 

Awesome info - I have a few questions for those of you w/ rear sway bar knowledge...


I have a stock '05 5AT TL, no plans to ever lower or to touch the suspension, I don't drive the car very hard, but would like a little more stiffness in my steering....

-Do you think it would be too much of a change to go from the stock 17mm to the Progress 24mm bar, if so, should I just go with the Comptech (22mm) whenever theyre back in stock instead?

-Does adding a RSB have any affect on driving during bad weather...like snow?

 

If you were only allowed to do one modification to your car then the RSB should be the one to do. I have the Comptech 22mm and the difference is like night and day. It won't completely eliminate body roll in turns but the difference it makes in everyday driving is incredible. I don't feel the rear corners trying to lift anymore. Also, it does not affect the overall feel of the suspension at all. Best bang for the buck in my opinion.
If you do go this route get the poly (red) busings as well. They're stiffer than the black rubber ones that came with the car and they're not expensive. I didn't get the greaseable ones and only noticed some squeaking during the cold winter months. And that was only when I traversed speed bumps, no squeaking in normal driving.
Good luck. You wont be disappointed.

 

Malu,
per your post in the BM, I'll also include a set of energy bushings and stainless mounting bolts if you want my Comptech bar.

 

thanks guys...anyone know about the snow question? (whether having an RSB improves/worsens/no affect on driving in snowy/icy conditions)

Thanks!

 

I had no problem in the snow and ice at all. Apart from the front spoiler on un-plowed side streets. It's a fwd car and the sway bar is for the rear.

 

I agree 110% with Shalooby, best bang for your buck. You will find yourself pushing the car in turns now because there very little to no roll. The next improvement I made which was more expensive was going to 19" Toyo T1R's on Volk wheels. The car amazes me every time I drive it.

 

Bump for the guy who asked me about sway bars.