Here's a chance for knowledgeable suspension guys to educate the rest of us:

What is the difference between a stock sway bar and a high-performance aftermarket sway bar? Why should someone pay a high price for an aftermarket bar? What are the benefits?

I am looking for perspectives from experienced owners. Guys who have spent the bucks on these parts and feel either pro or con toward them.

 

Well the stock sway bar, if you even have one, is not much thicker than a pencil. Most vettes don't even have one stock as it was more of a feature of the gymkhana suspension and other suspension packages.

With a thicker 5/8" or 3/4" rear sway bar you have less body roll. Bigger sway bars works well with lighter springs.

 

I vote for con. I like a firm ride, and I use the bars to tune the suspension. Some other forum members like a soft ride, and then get their roll stiffness with larger bars. Depends on what you drive on and how you drive it. My suggestion is to buy a good book explaining supension dynamics, and then make your choice.

 

Differences between the stock sway and a "performance" sway bars: Weight and price! That's it!!!
However - sway bars are needed.

Most everyone runs the front sway bar which is a factory item and really tightens up the font end while balancing suspension. Regardless of suspension types, almost all include a front sway bay to complete the final suspension package. Front sway bars are needed in most all cars!! The sway bar will balance your front end through cornering and hard bumps. As you round a turn, especially a hard turn at any speed, the sway bar will transfer the natural roll response/weight shift from the outside turn of the car to the opposite or inside turn of the car and in essence, keep the car grounded, increasing the tire/road contact. You can tighten or loosen the front sway bar by tightening/loosening the mounting bolts (to the frame/not control arms) and this effects front suspension, roll response, tire contact during cornering, independent bump absorption, etc. Tightening the mounts will tighten the rubber or poly mounts against the bar itself - tighter allows for less sway bar movement while lose allows increased play. The sway bar itself actually attaches to the lower control arms so your playing with the mount tension or increasing bar size will in fact affect the cornering and bump absorption ability of your front end, affecting drive(r) comfort.

I've had both a 1" and a 1-1/8" front sway bar in my Vette (350 Motor) and felt a slight difference between the two. The 1-1/8" (larger) bar was better for my needs but needed some adjusting. You should go with something similar for a 350 motor and drive the block a few times, tighten or loosen the mount bolts 1-2 turns and then drive again, repeat until you feel the best ride.

Keep your front sway bar as the front end of the car and front suspension absorbs most of the roll and corner response. Much more debate on the rear sway bar. If your on the track or running from the law on a lone road then you may desire a rear sway bar. However, I prefer for the rear to be completely independent and allow each side to respond separately to bumps in the road.

Differences between the standard and performance sway bar:
- Standard bars are solid steel and heavy
- Performance bars are tubular and lighter.
Both do the SAME thing!
Save the $$ and drive with half a tank of gas for weight savings.

 

With the above concerning front bars. These old Impala front ends need the bars.
The rear, as stated , is another debate. Putting a stiff rear bar in defeats the IRS. The rear end will not roll when cornering, and with a posi-trac differential, this means that both tires will break loose under heavy throttle in the corner. This may suit some drivers fine, ie. "drifters", but given the seat position in a C3 (on the rear axle) this can be quite sensational for drivers of road cars who like traction!
I think most who try the rear bar spin the car around once, and take it off. At least I did!
There's still some debate I'm sure as to the affect of different sizes and tightness, but Duntov didn't think the small-block car needed the rear bar, and he spent some time on it.

 

I'll assume you're asking about the difference between a stock bar and a performance bar (factory or otherwise) and not specifically about aftermarket bars.

I'll try to explain bars as they relate to ride & roll properties.

The first part of roll stiffness is ride. Going over hills & dips where the wheels on both sides move together. During ride motions like this, the bar does nothing as it moves up & down equally on both sides. Aside from a little friction in the bushings, it puts no forces into the suspension.

Ride motions need to be balanced front to rear and they need to be damped properly front to rear. This is done by making the springs an appropriate stiffness such that the natural frequency under vertical motions is something in the 1.1-1.5 Hz range. More sporty cars have a higher natural frequency. The natural frequency of the rear suspension is generally higher than the front. So when the car goes over a swell or through a dip, the back oscillates faster and catches up to the front.

So the spring rates are chosen to give an appropriate ride quality, and the dampers are tuned accordingly. In a production car, this is done with a broad range of customers in mind. The ride can't be too hard, or too soft. It needs to be tuned for the typical intended customer. So if you like a stiffer more performance-oriented suspension, you may find a factory tuned suspension lacking.

Now that we have the ride balanced with the springs and dampers, what happens when we go through a corner? The car's body rolls as there is a lateral force applied to the center of gravity of the vehicle. The amount a car rolls or leans in a turn is determined primarily by the stiffness of the springs, the roll center heights or the front and rear suspensions, and the height of the car's center of gravity (where the lateral force acts). So in a given corner, those things determine how much body lean there is.

But what if I don't want that much body lean? Simple. That's where stabilizer bars come in. If I want the body to roll less, I need to help out the springs with stabilizer bars. The beauty of them is that they work only when the car is leaning.....well, mostly kinda sorta. They also work when one side of the car hits a bump, but let's ignore that for now.

So how big do I make the bars? and do I put one on the front, rear, or both?

First it helps to understand what the bar does and how. How does it stop the body from leaning? Simply enough, if one wheel wants to go up, it forces the other one up as well. If one wants to go down, it forces the other down. So in a turn as the body leans, the inside wheel goes down (so the bar forces the outside wheel down), but the outside wheel is already trying to go up (so the bar tries to force the inside wheel up). The net result is the bar applies a certain amount of torque to the body that’s trying to keep it level. As it does so, load is transferred across the axle, and the bar tires to keep the body from leaning. The thicker/stiffer it is, the more lean it prevents, and the more load is transferred.

So what about the front/rear bar thing? Let’s ignore the front and look at the rear for a second. Suppose I don’t know better and I calculate that I need a big ol’ bar and I put it on the rear. So when I turn, there’s a lot of load transferred across the rear and very little at the front. As I turn, load is transferred, the car has a certain roll stiffness, and everything seems ok, right? Not quite….

Let’s expand that and suppose my car weighs 2000lb with a perfectly even weight distribution, so each tire starts with 500lb on it. When I put that bar on the rear, my load while cornering is maybe 200 on the inside tire and 800 on the outside. And maybe the outside front tire has something like 600lb on it and the inside front 400lb. How happy is that outside rear tire when it has to carry 800lb? Which tire is going to say f’ it first, the front or the rear? Yup. The rear. What happens when THAT happens? Uh huh. The cart suddenly ends up before the horse. Conversely, if it’s all in the front, the car pushes at the limit. Which is better for the normal driver?

So clearly we don’t want all of the roll stiffness in the rear, but how much DO I want in the rear? Generally, I want something close to the weight distribution of the car. So if a car has a 60% front weight bias, I want something on the order of 60% of the roll stiffness in the front. 50/50 car? I want the roll distribution closer to 50% front, give or take a few percent.

So what do you gain by going with stiffer stabilizer bars? (The same could be asked about what’s gained by going to urethane bushings instead of rubber, the results are related). That stiffer bar reduces body roll which keeps the body flatter and keeps the tires more vertical. This allows them to grip more. (with a lot of body lean, the tires camber/lean away from the corner which is not what you want them to do for maximum grip). There are other factors, but we’ll keep it simple (if a bit lengthy) for now.

If you increase the size of the front bar, you probably want to increase the size of the rear bar (or add one to a small block car) to keep the roll distribution balanced front to rear.

For C3’s, it’s generally accepted that good bar combinations are 1” front, 5/8” rear, 1 1/8 front/ ¾ rear, and 1 ¼” front 7/8” rear.

I recently upgraded from the stock front-only setup to the 1 ¼” front 7/8” rear on my ’69. Significant improvement in cornering. Body roll is incredibly low and cornering grip is significantly improved. Haven't even come close to spinning the car. I also have a gymkhana 7 leaf rear spring and unknown rate front springs (460 I assume) that have been cut 1 full coil.

As for the comments about loosening/tightening the mounts to the body, all I can say is The brackets should be tightened to the body to the proper torque. Rubber bushings should be pre-loaded (the bar should not droop on its own with rubber bushings if it’s detached from the control arms) and urethane bushings should be snug to the bar, never loose. The torque on the pogo sticks that attach the bar to the control arms will affect the rate at which the bar loads up and applies torque. If they were very soft, one wheel could move a bit before the bar gets too involved (good for ride) and if they were very hard/rigid, the bar would engage immediately (better for handling, at the expense of ride quality over even the slightest bump). The stiffness of the bushing at the body-side mount will also affect how quickly the bar reacts.

I hope that helps.

 

..........well done.......

 

DDE's explanation is right on.

 

Nicely stated, ddecart, but it's also worth pointing out that Guldstrand, for one, would recommend balancing the C3 without the rear bar.

 

there's a big difference in how the rear sway bars attach to the suspension. the factory bars attach directly to the trailing arm in a vertical way, but the after market bars attach to a strip of metal that's bolted to the trailing arm in a horizontal way. that horizontal piece of metal is going to bend, or the 5/16 bolts attaching it are going to break.

 

Excellent desription dedecart!!

For those who are NASCAR fans, take note that the loading up of the rear tires with more roll stiffness that dedecart explained is what makes the car "loose" in NASCAR terms. Conversely, unloading the rear, making the roll stiffness in the front greater than the rear, makes the car "tight" also referred to as making the car "push".

So, if the rear end wants to come around in a turn, especially on wet roads, you have too much rear roll stiffness relative to the front end of the car.

One mroe thing... I must second dedecart's comment about loosening the sway bar-to-frame mounting brackets. NEVER loosen these bolts to add free play. It could cause a failure in either the bracket or the bolt resulting in loss of sway bar control in a hard turn and could kill you.

 

One thing I did not mention is the whole solid vs hollow thing.

There are two ways to make a structural element stiffer: section and gage.

A thin walled tube that's 6" in diameter is stiffer in torsion than one that's only 1/2" in diameter. That's section.
A solid 1" bar is a stiffer torsion spring than a 1" hollow bar. That's gauge.

Why use one over the other? Cost, mass & performance.

• A hollow bar is more expensive and somewhat more difficult to form, and you need a larger dia bar for the same performance.
• A solid bar is less expensive, easier to form, and able to provide more roll stiffness for a given packaging space. But it's heavier.

Which one you use depends on how you want to trade off those qualities.