According to the books, '69 just has a front sway bar. I guess my first question is why not one in the rear? What are the consequences of installing a rear sway bar? Is there any benefit to installing a thicker one in the front? My understanding is that a sway bar only stiffens the frame on turns and does not affect ride quality any other time. A thicker bar will tighten the frame more on turns and adversely affect the ride more, but only on turns. Am I correct? What do you fellas recommend? I like to take country roads with sharp turns and I think this would be a fun upgrade for me.

 

I had the same question. Heres a bump for you, hope someone chimes in. Its a (relatively) cheap upgrade, but nothing's too cheap if its not worth anything.

I'll take it one step further, is the front sway bar a "wearable" item (ie. should I consider replacing this when sprucing up the suspension with new bushings, shocks, springs? No hijack meant...

 

All '69 big blocks had factory rear sway bars, easily added to SB cars, as well as aftermarket.

You're correct that a thicker bar would be stiffer but only typically felt under turns.

The sway bars (front or rear) are not wear items, but their end link bushings and mounting bushings do deteriorate and fail. That raises the unanswerable question about poly vs. rubber bushings.

Hope this helps.

Steve

 

Poly should be stiffer and last longer. I went to a highly reputable place several months ago to get some bushings put in my A-arms and he wanted to keep mine rubber. If a guy with 30 ~ 40 years of experience and a reputation to match says that, then I'll let him do it until I am able to mess with/up my suspension myself.

Anyways, should I assume I still have the front sway bar in my SB car? How thick is it? Where is it located? Is it worth upgrading if it's in there? In either case, what would I want to do in the rear? (What's popular size and make?)

 

69,
My bet is that you do still have the front sway bar. It's a long rod about a 5/8"to 3/4" in diameter that runs across the front suspension from the left lower a-arm to the right lower a-arm.
Think about buying an AIM and GM Chassis Service Manual for your car. They have LOTS of good information for not too much$$$.
Regards,
Alan

 

Adam, you have a front sway bar for sure. I saw it when we had it on the lift. You will remember we talked about the worn bushings on it.

I upgraded the sway bar on the 77 vette and it made a huge difference. I believe I put an 1 1/8 bar on the car. The sway bar keeps your wheels on the ground. It is the opposing force holding your chassis off the "A" arms. Other than your coil springs, there is nothing else holding your car off the ground.

My Big Block has a sway bar on the rear. I can show it to you the next time you come up. You can certainly install one on the back. It will help you in turns for sure, the car will not roll like an amusement game, and your wheels will have more force to the ground.

Can a sway bar wear out? Well, it is Spring Steel. Your leaf springs are made out of the same metal and they wear out. Never measured one though to see if it was different.

Rd

 

I added the rear sway bar when I did the full mechanical restoration of my '69 small block roadster. It truly makes a great improvement without a setback in ride.

 

Hold on.....A fat front sway bar may be good thing, but that not necessarily true for the rear. A rear bar diminishes the independent rear suspension and give you more of the feeling of a solid axle. It also has a tendancy to make the car "loose"- the rear end wants to come around on sharp turning. If you've got a 3/4- 1 1/8' front bar and your happy with the cornering under speed, then you probably shouldn't be persuaded by the marketers to install a rear bar. However, if you gotta have one, make it real skinny-like 5/8", and I'll bet your butt won't be kissin your face at speed on the twisties.

 

Go find a 65-74 BB car or a late 70's Vette with the Gymkahna suspension (front/rear bars) and bolt them on.

 

Are you familiar with the term "TTO" (Trailing Throttle Oversteer)?

However glowing reviews may be about them proceed with caution, as whenever you add or increase a rear bar the balance of your car is almost always going to shift towards, if not into oversteer. You could wind up with an unforgiving ride that makes it difficult to apply power on corner exit if you have any torque to speak of, and which is prone to spin should you be forced to abruptly lift mid turn.

Should your car have a fair balance beforehand, you're likely to find that you'll also need a larger front bar. If your car doesn't turn in well or plows thru turns and isn't suffering from excessive roll, I suggest that you first address improving front grip rather than simply taking it (grip) off the rear in a quest for balance at the expense of cornering capacity.

 

To answer that, let's step back and ask "Why does it even have a front bar?"

When the springs are chosen for a car, they're picked because of the way they make the car feel over normal ride motions. Nothing to do with handling....yet. The front springs are set to the desired stiffness and the rears are set to the desired stiffness in order to balance out the front. The rear wheels are made a little stiffer than the front (spring rate at the wheels, not the actual spring rate...that varies because of the suspension geometry). So when going through a normal dip or hump in the road the front reacts and then the rear reacts with motions that are a little quicker and effectively catches up to the rear. So when you go through that dip, the car bounces up & down and doesn't pitch forward & back.

Now what? The springs are holding the car off the ground (the bar doesn’t at all btw), the car is balanced for pure up & down ride motions and we haven't given too much thought to going around corners.

The springs don't just set the overall rate for the vertical motions. Because of the suspension geometry and the spring spacing across the car, they also provide resistance to body roll. How much? That's the key.

The front and rear springs combined determine how much the body rolls in a corner (without considering the bars yet). If that's more roll than desired, the car needs something to supplement the roll stiffness from the springs. That's where the bar comes in. Roll stiffness from the springs + roll stiffness from the bars = total roll stiffness => how much does the car roll in a corner.

So this answers the question of why the car has a bar at all, but why is the one it has in the front?

But once you calculate how much additional roll stiffness you need from the bars, where do you put it? That depends on where it already is from the springs. And we need to look at what’s happening with the tires.

When we corner, we’re transferring load from the inside tire to the outside. As the load on that outside tire increases, so does its ability to corner. More load = more cornering force. But it doesn’t increase it as fast as the cornering capability of the inside tire decreases. So the net effect is a decrease in the cornering ability.

So what? As long as the load transfer from inside to outside is the same on the front as the rear, they’ll both have the same increase in cornering capability on the outside and same decrease on the inside tire. But you can probably figure that if the load transfer isn’t balanced, either the front or the rear axle will have more or less capability and whichever one that is will lose traction first.

The purpose of the stabilizer bar being on the front is to make sure that it’s the front axle that loses traction, or “washes out”, first and that the car has limit understeer.

So why not on the rear, too? Simply put, it didn’t need it. To get the total roll stiffness they wanted and to keep the front at the limit before the rear, a relatively small front bar was all it took.

What would adding a rear bar do? It would increase the total roll stiffness, making the body roll less in corners, but it would also change the front/rear balance. So the rear would be more likely to lose cornering grip and wash out before the front. Not really desirable.

So what to do if you want more roll control? In order to keep the same balance front to rear, you need to increase the total rolls stiffness but also distribute it front to rear. So you end up adding a rear bar along with a bigger front.

But why did the big-block cars already have a rear bar? For starters, they’re heavier, so they needed more roll stiffness overall. When the engineers were developing that suspension, they determined that a rear bar was needed for proper balance. I suspect that the body roll on a big block is less than a small block, too.

A bit lengthy, but hopefully that helps.
Dave

 

Thanks for the great info

I had the gymkhana suspension RPO on my '81.
Sway bars are the only stock parts left on my chassis now.
As I installed poly bushing for the rear spring that are way much thicker than the rubber ones I have no room left in the T/A to install the sway bar
I was a little worried my car won't corner correctly.
After reading your explanations I think I don't need a rear sway bar because I improved my suspension and my engine is lighter now thanks to all the aluminium parts I put on it.

 

Well said ddecart. I've read whole chapters on bars in books dedicated to handling which didn't explain it as completely or as easy for non-engineering types to follow.

 

I've got a 1 1/8 front now. I have a 7/8 rear that will be installed & driven to evaluate. I "may" disconnect & remove this 7/8 rear bar later on based on how it performs.

 

Thanks, everyone, especially ddecart. It makes sense. So I wouldn't just want to add a sway bar or just go as big as possible. Did the Gymkana have 1 1/8 and 7/8? Would that be a likely combination to improve handling? I do get a little bit of roll on the country roads when I take turns fast. Will the bars help my cornering ability?

That being said if anyones runs across extra sway bars (as close to 1 1/8 F and 7/8 R as possible), feel free to PM me.

 

ddecart
thanks for the lucid explanation.
you say that the front bar ensures that the front of the car will lose traction before the rear and result in understeer. but it seems to me (afer reading your post) that the front bar will reduce body roll and increase traction, and therefore make the rear end looser in comparison and create oversteer.
jeff

 

I had the same question. I'm :

Also, I've got an offer for the front sway bar, anyone with a spare rear sway bar? I'd like to do it all at once and something close to 7/8 seems to be ideal for my rear.

 

Ahhhhh yes. Let me 'splain. I also have a chart that I'll have to find later that shows it graphically.

As the load increases on the outside tire, its cornering capability increases. But at the same time, the load is decreasing on the inside tire and its cornering capability is decreasing. The relationship between vertical load & cornering force capability isn't linear. So the loaded tire gains cornering capability at a slower rate than the inside tire loses it. The NET effect is that the total cornering force on the axle is lowered by the cornering load transfer.

So the stiffer the bar on that end of the car, the more of the load transfer that happens on that end, and the lower the total cornering capability of that axle is (relatively speaking as the load is transferred in a corner).

 

ddecart
i know it's monday-but, when you say that a stiffer bar allows more load transfer, you lose me. shouldn't a stiffer bar reduce body roll, and therefore reduce load transfer? or are you referring to the opposite axle, ie rear of car?

 

I think he means that a stiffer (larger diameter bar) transfers more downforce to the other wheel and improves cornering overall since the curve is not linear (very cool to know). So another question, is let's say 1 1/8 up front and 7/8 in back is a proven combination. Would a 1 1/4 up front be too stiff and feel unbalanced in a turn? Would you notice a positive or negative difference?