General Suspension Info for Newbies- Sway Bars

[Electrofied]

I get asked a lot of questions everyday about suspension and how/what can the customer do to improve it.

This is mostly for the newbies out there, which all of us have been at one point.

If you do nothing else to your suspension I recommend at least installing sway bars. They will greatly diminish the body roll which makes your car push to the outside of a turn.

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. Relative 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. Okay... 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 are at their limits. Otherwise you turn in quickly, the tires grip, then the body finally finishes leaning, when it stops, the tires lose grip. This is especially noticeable 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 tire cross 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 McPherson 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 is 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 already a non-issue. The car doesn't lean much with 500 lb springs. They use their bars to change the balance of the car. Here are 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 (pushing), 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 okay. But every time 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). That decreases the weight on the rear inside tire. Decrease the size of the 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 transferred weight to the other end of the car.
So that's it. How they work and what they do


Electrofied



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[bookeem]

great post...

[mhigham]

Good post, I'm sure that answers a lot of questions and now all you will get is "Which sways whould I get?".....

Mike

[Super T]

Pretty thorough explanation, well done. Would you be so kind as to comment on how they harm/hurt you in a straight forward 1/4 mile style drag race with no cornering?

[MattRobertson]

Very well done. Beans to you. Usually when talking to people who want to stiffen their suspension I don't recommend sways unless they are committed to being able to corner the car well. If they just want less float on their suspension and a firmer ride without the 'rolling brick' effect a sway bar will add on uneven bumps, I suggest a coilover system. The ST coilovers available at HHP are probably the best option for the budget-conscious.

[Electrofied]

Pretty thorough explanation, well done. Would you be so kind as to comment on how they harm/hurt you in a straight forward 1/4 mile style drag race with no cornering?

Good question...
In talking to numerous drag racers, and I have yet to try it on my car and not sure I would. The Mustang group unbolts their front sways when drag racing.

Swaybars are most definately a plus for daily driving and road courses, but they are not benefical to drag racing.

Even coil-overs have been known to kill one 1/4 mile time with the exception of the V2's where one can adjust them a bit to get the weight transferred rearward for some traction.

E

[moparman53]

Thanks for a very informing article.

[MoparPosterChild]

Wow.

[RacingRev 1320]

that actually made sense. great job explaining, in laymen's terms, a subject that had me scratching my head

[Ghostface Mag]

Nice write up J.....

[joseph]

Guess it's not on my list of mods anymore, becuase I don't want a harsher ride when going over speedbumps sideways.

[Braddah Jay]

Is the swaybar any help with an air ride set up?

[Dan79]

What about the SRT8? I've heard different things about their sways. Some articles say they're bigger than the RT's and some say they're the same. Are antisways necessary on the SRT8s with the lower ride height and stiffer suspension?

[Buckhemi426]

Right on for the info. bro. Now i might not sound so dumb when i get ready to order a setup.

[MR. J]

Awesome post.