sway bars

[HeWhoKillz]

I have a question. Do sway bars generally come in a pair for the front and back of a vehicle? Or is there only one for the front or only one for the back? I have a 91 corolla and I don't see how a sway bar would even go on in the back. Is there only a sway bar in the front of a vehicle? I need help.

[curtis73]

Depends on the vehicle. Most FWD cars only have front sway bars. A rear One could probably be adapted/engineered for your car, but it probably wouldn't do much good. FWD cars have most of their weight on the front as well as the power in the front. That tends to make them understeer. Adding a stiffer bar up front can make that worse.

Most RWD cars have both. Typically tuning them both will net the best handling. Most manufacturers offer a "matched" set if a car came with two, but manufacturers have to design things for the lawyers and bean counters, meaning they design the front bars a little too stiff to maintain understeer properties. Its a bit safer for amateur drivers that way. Often times its trial and error, or just finding out what others have done on your specific car. Many of us GM B-body guys use a Hotchkis front bar with a Herb Adams rear bar instead of the "matched" set from either manufacturer; depending on how we use the car and our driving style. I tend to drive heavy on the gas, so I need a little less rear bar to prevent oversteer. If you're a more experienced driver you might want a little more neutral feel.

But, (no offense intended at all concerning your corolla) my guess is that a sway bar won't do much in that chassis. It was never designed for heavy corner carving so the unibody isn't very stiff. Any additional weight transfer you put through the body with a stiffer bar will just flex the body that much more. Not dangerous or damaging, just know that tidbit so you don't expect too much from its handling.

I think the next step is to find out what others have done in their 'rollas and use their experience.

[Alastor187]

Originally Posted by curtis73

But, (no offense intended at all concerning your corolla) my guess is that a sway bar won't do much in that chassis. It was never designed for heavy corner carving so the unibody isn't very stiff. Any additional weight transfer you put through the body with a stiffer bar will just flex the body that much more. Not dangerous or damaging, just know that tidbit so you don't expect too much from its handling.

Wouldn’t a sway bar have more impact on a less rigid chassis?

[curtis73]

Originally Posted by Alastor187

Wouldn’t a sway bar have more impact on a less rigid chassis?

No. As with all weight transfer during cornering, the component in question transfers force from the body's weight. If the body itself is flexing, less of the force is transferred to the component.

Say for instance you have a spring on a scale. If you push down on the spring with a piece of steel, all the force is being transferred to the spring. If you push on the spring with a marshmallow, a fair amount of the force is being absorbed by the compression of the marshmallow and the spring moves less. The same goes for sway bars. In a turn, if you're transferring 1000# of weight, if some of that transfer is taken up by body flex, less of that weight is handled by the sway bar. In this way the sway bar seems looser on a flimsy body since the flimsy body absorbs more of the transfer.

In the same way, if you have a unibody that is infinitely inflexible (no flex at all), ALL of the weight transfer is handled by the suspension components. As a body gets more and more limp, the weight transfer becomes less and less dependent on the rates of the suspension components. A 500# per inch spring will handle flatter on a tight body than a 500# per inch spring on a loose body.

[Alastor187]

Originally Posted by curtis73

No. As with all weight transfer during cornering, the component in question transfers force from the body's weight. If the body itself is flexing, less of the force is transferred to the component.

When I think of a front sway bar, I am thinking of one that connects between the strut towers. So when the body becomes loaded without the sway bar, the body deforms and the tops of the strut tower flex towards each other. When the strut bar is present then the tops of the towers are held at a fixed distance. The only way for the towers to move towards each other is if the strut bar is deformed.

In this sense it would seem to me that a very flexible body would allow a lot of movement of the strut tower. So adding a very stiff member between the towers should have a significant impact.

On the other hand I think understand what you saying, and that is even if the sway bar coupled the strut tower, the body flex would still allow a lot of coupled motion.

Originally Posted by curtis73

Say for instance you have a spring on a scale. If you push down on the spring with a piece of steel, all the force is being transferred to the spring. If you push on the spring with a marshmallow, a fair amount of the force is being absorbed by the compression of the marshmallow and the spring moves less. The same goes for sway bars. In a turn, if you're transferring 1000# of weight, if some of that transfer is taken up by body flex, less of that weight is handled by the sway bar. In this way the sway bar seems looser on a flimsy body since the flimsy body absorbs more of the transfer.

I am not sure this example really makes sense. If you push with the same force then the scale should read the same weight regardless of the marshmallows presence. At least ignoring any hysteresis induced losses, which I don’t think you are referring to.

I think a better example is just two spring in series on a scale. If they are both stiff and a load is applied there will be little deflection but the scale will read a weight equal to the load. If one spring is stiff and the other soft and the load is applied, the scale will read the same weight but the deflection will be much higher.

Originally Posted by curtis73

In the same way, if you have a unibody that is infinitely inflexible (no flex at all), ALL of the weight transfer is handled by the suspension components. As a body gets more and more limp, the weight transfer becomes less and less dependent on the rates of the suspension components. A 500# per inch spring will handle flatter on a tight body than a 500# per inch spring on a loose body.

This makes sense.

My question is exactly how does the load transfer through the body when a sway bar is present. If you were to consider the body a spring and the sway bar a sping, are they more in parallel or series.

[HeWhoKillz]

But, (no offense intended at all concerning your corolla) my guess is that a sway bar won't do much in that chassis. It was never designed for heavy corner carving so the unibody isn't very stiff. Any additional weight transfer you put through the body with a stiffer bar will just flex the body that much more. Not dangerous or damaging, just know that tidbit so you don't expect too much from its handling.

[quote]


None taken. Its front wheel drive. Can you possibly explain how the "flexing" of the body works.

I think the next step is to find out what others have done in their 'rollas and use their experience.[quote]

How many other people do you know that uses a 91 corolla and tries to enhance its preformance. lol. Not many. What do I do now?

[HeWhoKillz]

With the flexing thing sounding so bad, what about this item?

http://www.customstreetdesigns.com/1177-ARO651005.htm

[turtlecrxsi]

Curtis, please correct me if I'm mistaken but "sway bars" and upper "strut tower bars/braces" are NOT the same.

[GreyGoose006]

they are completely different.
sway bars are for eliminating body roll
strut towe braces are for stiffening a weak body

the strut tower brace might help with some of the body flex, but not all of it.

as for the marshmallow example, curtis is right. kinda.
although puttig a marshmallow on top of a spring and pushing on it will not change the fact that 10 newtons of force or whatever is being applied, it will affect the springs travel, and response.

in a cars suspension, the travel is fixed, so if you have a wishy washy body, then the suspension can only work so well... even if it was designed by lotus.

so curtis was right, but he used a bad example

if your body is flexing, your suspension becomes less of an issue.

[turtlecrxsi]

Thanks greygoose for clarifying. I hear a lot of people mistake strut tower braces for sway bars but I normally keep my mouth shut.

[GreyGoose006]

yeah
strut tower braces go under the hood and connect the two strut towers.
sway bars go under the car and connect the body to the suspension.

[turtlecrxsi]

Yep. My crx had all of them. Front and Rear Strut Tower Braces and Front and Rear Sway Bars.

[Black Lotus]

Don't worry about the friggin' body flexing unless you are going road racing.
Just put it out of your mind. Forget about it.
Find a rear bar for the car and see if you like it. Keep an eye out for oversteer. You do NOT want a car that oversteers in steady state cornering. You do not really even want a neutral steering car. You want mild understeer unless you are an Auto-Xing weirdo.
If the car oversteers a bit with the new rear bar, put a slightly thicker bar up front.
Keep the front springs/bar as soft as you can. This maximises front traction in both acceleration and cornering. Try to make the rear of the car take out as much of the body roll as possible. Put enough bar in the back so the inside rear just lifts off the ground in a corner.
Enjoy,
Brian

[Alastor187]

Originally Posted by GreyGoose006

they are completely different.
sway bars are for eliminating body roll
strut towe braces are for stiffening a weak body

Stut tower bar ≠ sway bar

[curtis73]

Right... we're all on the same page now

Its just that tuning a suspension is much more predictable without body flex. It will always be there in some degree, but if you put a pair of 700# per inch springs in a 100% rigid frame, then you can expect 700# per inch. Flexibility in the body/frame means unpredictable weight transfer.

That was my marshmallow reference... poorly phrased. If you have a 700# spring on a scale and push down one inch, the scale reads 700# (plus the weight of the spring of course). If you put a marshmallow on top of the spring and push down one linear inch, the scale won't read 700#. The analogy was, the marshmallow (flexible body) acts like an additional spring. That makes the actual effective spring rate seen at the roll center of the vehicle is much less than 700#. Without the marshmallow, suspension tuning is much more predictable.

Suspension tuning for handling is all about using sway bars, springs, and other bits to determine how much weight gets transferred to the outside wheels in a turn. In a perfectly rigid car, its a simple math calculation. Since all cars flex some, its trial and error.

I had so much fun once trying different bars on an Aries K. I kept shortening the linkage to the sway bar so that the same control arm movement effected more on the sway bar which artificially increased its rate. I figured I'd get to a point where understeer became a problem but I never did. Later I found that the body was flexing so much that the hood contacted the fenders at the opposite corners during cornering, and then finally one time the hood popped out of its home. The additional sway bar "rate" was more than overpowering the flimsy K-car chassis to the point where additional sway bar rate did no good... it just flexed the body more.