Rear Sway Bar Question

[dagnabbitt]

I've read numerous threads on the efficacy of rear sway bars in our trucks... and as usual when I do that, I am not sure what to believe. The most informative threads are 10+ years old and are authored by former members, and I see no point in resurrecting them, so bear with me please.

I have two questions:

1. Is there any particular reason to NOT put a rear swaybar on a truck. Never mind a person's budget - lets say it is unlimited - or if it does little to improve handling vs the time and effort. Is installing a rear swaybar on a 2dw - stock or lowered, 1/2 or 3/4 - generally a good idea... or a bad idea.

2. There seems to be some disagreement over the efficacy of a rear swaybar in a coil spring truck vs a leaf spring truck. Is this a consideration, or a red herring. Is it a handling upgrade, regardless of the type of rear suspension?

I'd love to hear from you, thanks.

[Willie Makeit]

Never found a rear sway bar on these trucks to be worth the trouble or the cost for such little gains.

The front is an entirely different story, the bigger the better.

[theastronaut]

I had a '66 C10 I built a few years back with roughly a 5/7 drop, relocated shocks, and front/rear bars. I used a CPP front bar and an 80's F150/Bronco rear bar (nearly a direct bolt on). The bars eliminated any body roll but I wouldn't say it "handled" better, mainly because I was running tall/skinny high treadwear/hard compound 15" tires that limited how much grip it had in corners.

My current '66 with pretty much the same suspension setup minus any bars has some body roll but not enough to bother fixing with sway bars (even with a heavy wood framed camper shell) and is again limited in cornering grip by the tall/skinny cruiser-spec tires. I tow with it a good bit and it's dead stable even at 80 mph without sway bars.

If you're running regular tires and aren't pushing it hard in corners then there isn't really a need for them. They do compromise ride quality by making the suspension less independent, which is pretty noticeable on cars/trucks with stiff sway bars.

[leegreen]

I did not notice the change when I removed a rear sway bar on trailing arm truck.
I'd expect more handling gains from money spent on tires than on a rear sway bar

[dagnabbitt]

Thanks for the replies, my takeaway is that even if it required zero cost or zero
effort, most people would not put a rear swaybar on these trucks. Good to know.

[leegreen]

I'd put it this way:

drive your truck for a while with the tires, ride height and load you want to be typical.
If you find you have too much understeer when you drive the way you want your truck set up for, then you either have too stiff a bar in the front or need to add a rear bar

if you find you have oversteer then you either need stiffer in the front or less rear bar (or less throttle!)

generally stiffer = less grip, this is because tire grip more or less goes up with increased load, a stiffer bar distributes the load between the two wheels more so reduces the grip of the outside tire in a corner. So lightly loaded pickup rear axle probably does not need a rear sway bar.
It is generally considered safer for street cars to have understeer. But a rear bar may make it easier to get the back kicked out for some smoky drifting action if that is your game

There is a lot of handling information online and many people will describe it better than I just did. I suggest looking at autocross forums where people talk about adjusting for better handling rather than 'spending money' threads.

Another way to look at it is, what 2wd solid axle trucks came from factory with a rear sway bar? I don't believe that is very common

[dagnabbitt]

Originally Posted by leegreen

what 2wd solid axle trucks came from factory with a rear sway bar? I don't believe that is very common

They were factory with SRW trucks in and around 1973-74 (and maybe later) with the Z81 Camper Special option. I believe that I also have seen them on CUCV trucks, maybe the 1.25 ton ones.

I agree that part of improving a truck is to test it and add one thing at a time. There are so many configurations, though, that I wondered if a rear sway bar was always a positive (even a minimal positive), or if it could sometimes be harmful to your ride. That's why I phrased my question as an "if you didn't care about the cost or effort" way.

Since rear sway bars are on everything from Camaros to Camper Specials I would assume that they are for vehicles with uneven weight distribution, an odd center of gravity, which may carry a payload, or which do a lot of hard cornering. I have trucks that do some or all of that but none of which have a swaybar. I was wondering if they would benefit. I will do some more driving (and reading!) and see.

Also: still wondering if the leaf or spring rear end makes any difference at all to a rear swaybar.

[leegreen]

A 1500 pound camper with center of gravity 36" above bed floor is a really good argument for a rear sway bar.

read up on autocross and Camaro rear sway bars, some people take them off.
But now we are talking a driving scenario where things like tire pressure and shock adjustment can be equally as important as having a sway bar or not
No-one would buy a new sporty car that did not have a rear sway bar. That does not imply that all cars and trucks need one to be sporty

the c10 trailing arm rear has a reputation for more articulation than the leaf sprung version, so in situations where a sway bar is called for the coil sprung truck would need it first. Chevrolet dropped the trailing arm setup as the leaf spring rear had a better reputation as 'heavy duty'. Around the same time manufacturers all started down the path of marketing payload and towing capacity.

[dagnabbitt]

Thanks! that's very informative.

Of the trucks in my sig, I was thinking about the 1970 SWB C10 - which is a trailing arm coil truck that I plan to lower and LS swap, and my 1968 C20 which is also trailing arm coil truck that might haul a slide in camper. I would of course be adding a front swaybar to both of these trucks before getting rears.

My 1981 SWB is lowered and has 400+HP, and it does have a front swaybar. Since I recently added posi I was wondering if I should go all the way and put a rear swaybar on it, too. It is really fun to drive fast, and I want to get the most out of it. Now that it is free from transmission shop hell I will drive it some more and see how it feels. Cornering is definitely different with the posi.

I will keep reading up on this, but if anyone has an opinion, I would love to hear it still.

[theastronaut]

Relocating the rear shocks on a trailing arm truck makes a huge difference in stability and sway, I'd argue it's more important to do that than having a sway bar since having a better motion ratio for the shock improves all aspects of driving, not just body roll. I could see the benefit of a rear bar with a slide in camper, those are really heavy.


I copied FrizzleFry's method in this thread:

https://67-72chevytrucks.com/vboard/...d.php?t=468892


This is my current '66 I mentioned in my first post- it has a very heavy wood framed camper shell, relocated rear shocks, D2600 bags in place of the stock springs, and wider 8" wheels with 235/75 rear tires. The wider stance plus relocated shocks keeps the rear of the truck dead stable even with the total truck/trailer weight coming in near 9,000 lbs. I've taken it up to 80 mph when towing and its smooth and goes dead straight down the road with zero wiggle or sway. It doesn't have front or rear sway bars, but does have gas shocks and better shock geometry that do a great job of controlling body motion. The only complaint I have it that while it works great when it's loaded, the shock valving is too stiff when it's empty, so I'm looking into shocks with adjustable valving.

[D.B]

How about an Anti-Roll Bar instead of a Sway Bar. Sway bars are designed to have some flex, but an Anti-Roll Bar is not designed to. I noticed some aftermarket rear sport suspensions use anti-roll bars.

[leegreen]

Hey astronaut, any issues with shock bushings not lasting with that outboard shock setup? I've considered the same mod off and on, but the way the relocation will work the bushing angles has concerned me.

your post just rekindled my interest!

[theastronaut]

Originally Posted by leegreen

Hey astronaut, any issues with shock bushings not lasting with that outboard shock setup? I've considered the same mod off and on, but the way the relocation will work the bushing angles has concerned me.

your post just rekindled my interest!

No problems out of them, I've put 21k miles on it with this setup.

[theastronaut]

Originally Posted by D.B

How about an Anti-Roll Bar instead of a Sway Bar. Sway bars are designed to have some flex, but an Anti-Roll Bar is not designed to. I noticed some aftermarket rear sport suspensions use anti-roll bars.

They're the same thing, some are just more rigid than others.

[D.B]

Originally Posted by theastronaut

They're the same thing, some are just more rigid than others.

Well, I used to think they were the same thing, but they are not. A sway bar is made from spring steel and would flex to help reduce body roll. An anti-roll bar is not designed to flex. I's designed to prevent body roll.
So, my S10 drag truck was lifting the front wheels and twisting the body. Suspension guy said I needed an anti-roll bar. I put one in and now it lifts the wheels straight and the truck ran faster and has quicker 60 ft times.

[MellowYellow70]

I'm real coilovers on my trailing arm 70 C10. Without the rear swaybar I'd pick the front left tire over a foot off the ground on a hard launch, then when towing my race week popup, it would sway all over with the helper bags driving on the road. Adding the rear sway bar cured the wheelie launches (dropping 0.1-0.3 off 60ft) and tremendously helped hard braking sway with the camper.

[66 C10 383]

Say you have a normal everday street car with production size tire. You gently glide into a sweeping left hand curve on the highway and the car would "roll" towards the right hand side. So they run an "anti-roll" bar. A U-shaped bar that, as one side goes down it forces to other side to go up, thus keeping the suspension more level.

Now with more speeds & better tires, those same forces act the same but at more elevated rates. The bars, among other suspension parts, need to be beefier. That's why the wife's LeSabre has smaller sway bars than your autocross car does.

The LeSabre front bar may only be 5/16" where your race prepped sports car has a hollow light-weight 1.5" bar on front with your 335/30/18 sticky tires for autocross. The smaller bar will naturally have more flex to provide a compromise ride of cornering and ride comfort. The bigger bar with no flex is an all-out, in your face race piece with one purpose in mind. To keep that car flat in the corners at all costs.

Those same forces act on a car/truck when engine torque is applied. Even a 3.8 Monte Carlo torques to the right with even a small amount of gas is given when sitting at idle.

Big horsepower, sticky tires, and instant acceleration will cause the suspension to want to "roll" in the same direction, towards the right. That's why the left front tire unloads off the ground first.

So, you install a rear "anti-roll" bar on the rear so it will even out the loads from left to right. It tries to roll to the right but the bar prevents this and forces the left side back level. You come straight off the line with both sides of the suspension (and tires) being the same on both sides.

So, whether you have a bar on the front for street use, one on the front and rear for handling and/or racing, or one on the rear for launching, a sway bar, anti-sway bar, or anti-roll bars are indeed - all the same thing. Different manufacturers at the time called them differing names, just like with a posi rear diff, posi-traction, no-slip, limited slip, etc.

Let's just hope you don't have to employ your roll bar into this. That's when you're having a bad day ...

[theastronaut]

Originally Posted by 66 C10 383

Say you have a normal everday street car with production size tire. You gently glide into a sweeping left hand curve on the highway and the car would "roll" towards the right hand side. So they run an "anti-roll" bar. A U-shaped bar that, as one side goes down it forces to other side to go up, thus keeping the suspension more level.

Now with more speeds & better tires, those same forces act the same but at more elevated rates. The bars, among other suspension parts, need to be beefier. That's why the wife's LeSabre has smaller sway bars than your autocross car does.

The LeSabre front bar may only be 5/16" where your race prepped sports car has a hollow light-weight 1.5" bar on front with your 335/30/18 sticky tires for autocross. The smaller bar will naturally have more flex to provide a compromise ride of cornering and ride comfort. The bigger bar with no flex is an all-out, in your face race piece with one purpose in mind. To keep that car flat in the corners at all costs.

Those same forces act on a car/truck when engine torque is applied. Even a 3.8 Monte Carlo torques to the right with even a small amount of gas is given when sitting at idle.

Big horsepower, sticky tires, and instant acceleration will cause the suspension to want to "roll" in the same direction, towards the right. That's why the left front tire unloads off the ground first.

So, you install a rear "anti-roll" bar on the rear so it will even out the loads from left to right. It tries to roll to the right but the bar prevents this and forces the left side back level. You come straight off the line with both sides of the suspension (and tires) being the same on both sides.

So, whether you have a bar on the front for street use, one on the front and rear for handling and/or racing, or one on the rear for launching, a sway bar, anti-sway bar, or anti-roll bars are indeed - all the same thing. Different manufacturers at the time called them differing names, just like with a posi rear diff, posi-traction, no-slip, limited slip, etc.

Let's just hope you don't have to employ your roll bar into this. That's when you're having a bad day ...

Yes, same thing, different names sometimes but same effect, just more or less flexible.

[HO455]

Originally Posted by dagnabbitt

Also: still wondering if the leaf or spring rear end makes any difference at all to a rear swaybar.

I believe the biggest difference in the two is that most of the trailing arm suspension rear swaybar kit are poorly designed and fairly ineffective. Outside of generating sales for the vendor they don't do much.

See the photo. The bar connects to the trailing arm in front of the springs. Thus the bar only moves a fraction of the total movement of the axle. And this is one of the better designed sway bars commonly available. Some others have the connection even farther away from the axle.

Sway bars don't provide linear resistance to force applied. More movement or twist the more resistance. So with reduced movement the resistance is reduced making the bar ineffective. Especially if it was sized to match a common leaf spring bar size.

[Richard]

It seems to me that the stock stamped and welded trailing arms are designed to have flex. Not an engineer, but I see the aftermarket square and round tube trailing arms will flex less. So just installing those aftermarket arms is kind of like adding a sway bar. JMHO.

[LS short box]

Just a question sway bar wise.
Would a sway bar like for a 72 Chevelle that only attaches to the lower control arms be effective on a stock C10 trailing arms?
The Chevelle is a 4 link suspension.

[SCOTI]

Originally Posted by Richard

It seems to me that the stock stamped and welded trailing arms are designed to have flex. Not an engineer, but I see the aftermarket square and round tube trailing arms will flex less. So just installing those aftermarket arms is kind of like adding a sway bar. JMHO.

Correct. OE truck arms were designed & intended to 'flex' for articulation. The I-beam construction (two c-channels butt welded together like a beam) allow for some slight twist as well as the rubber bushed front locating bushings.

Many aftermarket truck arms shifted to solid tube construction (round or square) w/Poly bushed front bushings. Aftermarket solid tube truck arms w/poly front bushings tied to a rear end is one giant sway bar. Adding an aftermarket 'sway bar' is a money grab for a great majority of C10's using these solid tube T/A set-ups.

Stock 6x-72 GM truck arm suspensions need to articulate so the ride (and chassis reactions) are more predictable, consistent, & controlled.

If using a rear sway bar, one that mounts to the rear end yields the best bang for the buck.

[leegreen]

Originally Posted by LS short box

Just a question sway bar wise.
Would a sway bar like for a 72 Chevelle that only attaches to the lower control arms be effective on a stock C10 trailing arms?
The Chevelle is a 4 link suspension.

No. The ends of the arms are the axle never twist in relation to each other so that style of sway bar will do nothing. I have seen them installed in the past, doing nothing but adding weight.

Look for a sway bar that mounts to rear axle with the ends attached to frame. I have one from a 3rd gen Camaro that I think will work turned around backwards

[SCOTI]

Originally Posted by LS short box

Just a question sway bar wise.
Would a sway bar like for a 72 Chevelle that only attaches to the lower control arms be effective on a stock C10 trailing arms?
The Chevelle is a 4 link suspension.

Originally Posted by leegreen

No. The ends of the arms are the axle never twist in relation to each other so that style of sway bar will do nothing. I have seen them installed in the past, doing nothing but adding weight.

Look for a sway bar that mounts to rear axle with the ends attached to frame. I have one from a 3rd gen Camaro that I think will work turned around backwards

The A/G/B body GM C4L (converging four link) suspension under a Chevelle w/the sway bar bolted to the lower trailing arms is as effective as a sway bar mounted to the front side of the housing on a GM truck-arm set-up.

The Chevelle/Malibu factory sway bars induce bind @ the lower arms making the already compromised arrangement worse. Fine for the average skinny tire grocery getter Sunday driver but not so much a performance benefit. A/G body guys that are upgrading will utilize a rear bar that attaches to the rear end housing & anchors at the frame rails.

[mike16]

Originally Posted by dagnabbitt

Thanks for the replies, my takeaway is that even if it required zero cost or zero
effort, most people would not put a rear swaybar on these trucks. Good to know.

No.

It is not as effective as a front bar but it's improvement is noticeable.

It is less effective on a trailing arm truck and more effective on leaf springs trucks.

I have looked very carefully into rear anti sway bars for trailing arm trucks and can't see how the ones being sold currently seem to work.

With the trailing arm geometry the sway bar seems to act more like a helper or auxiliary spring.