paulmoore

Well as my project continues, I will be in the market soon for a complete suspensions overhaul. I AM A SUSPENSION *****!!!, and will put anything and everything on my car to make it as stiff and rigid as possible. With that being said, I was looking at some swaybars. I like the Hotchkis sport swaybars, and they come in at a decent 36mm hollow and 25mm hollow. Now, a quick check at BMR's website(www.bmrfabrication.com) shows that they have swaybars that are 32mm solid and 21mm solid. They also *claim* that the front bar is 40% more rigid than the 1LE front swaybar. So which is better, hollow or solid? I will be using the car for many purposes including but not limited to, drag racing, road racing and auto cross. I will be using Eibach Pro Kit springs with either Bilsteins or Koni reds. Another major factor that I have to consider is a color scheme for the underside of the car. Because of this, I am having to plan out the whole suspension before I buy anything so that I know what parts I'm getting and if they will fit into the scheme. Sorry if that seems ****, but that's just how I am. Anyone have any info that they would like to share? Thanks, Paul Moore

Dale

iTrader: (12)

A solid bar made of proper matieral is stiffer then that of its same size in hollow.

But once you start comparing different materials, different sizes, its a whole nother story. Its then up to company claims and/or people who have used them on similer setup as you plan to use.

Also, each driver likes something different per his/her driving style. Some like a loose rear, while some like a solid rear.

SDIF

I would have thought that the hollow one would be stiffer.

I did NOT major in Physics, but I have twisted a socket extension, but never a tube of any diameter.

HawaiianRS

Basically, given a solid and hollow bar of the same diameter and material the solid bar is stiffer. The advantage of hollow bar is that it is radically lighter while only losing a small amount of stiffness. There are lots of variables and math that's beyond me to consider. But in short a slightly larger hollow bar will give the same stifness and weigh a lot less.

Apeiron

You weren't trying hard enough then.

ME Leigh

Yep.

The moment of interia has a higher effect the farther the mass is from the center of rotation. So the mass or metal in the middle doesn't really help or produce much force be itself. Really on the mass on the other most edge is the only thing doing much.

If i could go with a solid or hollow bar of the same size i would always choose the hollow. There is no reason not to your lossing lots of mass and no stiffness.

FWIW i have a 36mm hollow bar in front and 21mm solid in the rear.

83 Crossfire TA

iTrader: (2)

Roll bar stiffness (rate) works out to be roughly:
(500,000 * diameter)^4 / (.4244 * link offset * center section length)^2 + (.2264 * arm length)^3
(in standard units… assuming a fairly straight bar, close enough to get useable numbers with)

From there you can see that the roll bar stiffness is proportionate to the ^4 of the diameter of the bar, IE, the diameter has a bigger effect then anything else. To calculate the stiffness of a hollow bar you basically calculate the stiffness of the bar as if it was a solid one, and then subtract the stiffness of a bar that has the diameter of the open space inside the hollow one.

Now I don’t know the wall thickness of a stock, hollow bar, but doing the math it only has to be thicker then about 3.5mm for it to be stiffer then one of the 32mm solid bars. Judging from the thickness of the metal where the drain holes are drilled on the hollow bars I would guess that they’re about 4mm thick, IE, stiffer then the smaller solid bars.

FWIW, somewhere I have exact weights, but the 32mm solid bar that I have in the garage is around 32lb and the 36 that I have is in the 13# range. It’s a BIG weight savings. (huh, if I could dig up the exact weights from when I weighed them then I should be able to calculate with some reasonable precision what the actual average wall thickness of the hollow bar is, since the 2 bars are almost exactly the same otherwise)

JPrevost

Hollow is better unless you've tested them back to back and have proof that the solid bar is turning better results... just trust the holloe bar . Now if you're out in the desert or rally car racing where you might hit big rocks well then go solid so that you HAVE a sway bar at the end of the race . Else hollow for all the reasons people gave you.

83 Crossfire TA

iTrader: (2)

Man, I can’t imagine what you could possibly hit hard enough that came up high enough that it would hurt a hollow bar that wouldn’t take out a dozen other things before and after it. If you’re worried about that then you have other problems.

RTFC

Here's a good read- it show a study on the subject with proofs and equations.


http://www.whiteline.com.au/docs/bul...%20Swaybar.pdf

berly83

I have the huge spohn solid ones and I have zero body roll. I autocross and those swaybars made a huge difference.

kalel21

Does Spohn make hollow sway bars?

Igor

What size are your spohn sway bars?

Thanks.

CheezX

You get much better stiffness to weight ratio with a hollow bar. No reason to go with solid, unless they're made of inferior metal and aren't heat treated after forming. Then in that case you'd need a solid one or else it would break (don't buy cheap crap).

Kat

iTrader: (4)

34mm/24mm, Hot formed, 4140 heat treaded bars.

Kat

soulbounder

I figured Kat would post something.

Now tell us how much Spohn's sway bars weigh.

Kat

iTrader: (4)

lol

I agree, they are heavy, in this case the performance out weighs the disadvantage. Yes the pun was intended.

Ron over on NE3G figured out the Spohn 34mm soild bar to be something like 20%-22% stiffer than the 36mm hollow bar.

Kat

CheezX

To get a 22% stiffness increase going to a 34mm solid bar from 36mm hollow would also be a 117% weight increase (not including swaybar arm bending).

I don't know, I'm definately not sold on that idea. Unless someone is forced by rules to keep their stock spring stiffness, they really wouldn't need that increase. With a stiffer spring, often better results are achieved by going with a smaller swaybar.

Or, another way to look at it. To achieve the same stiffness increase with a hollow bar you'd need 38.2mm OD, but instead only a 7% weight increase. Why add so much dead weight to your car? Isn't that detrimental to performance?

Kat

iTrader: (4)

Depends on who you want to argue with.

Kat

Dewey316

Who is going to argue, that adding weight is a good idea?

or is this another lesson is your companies engineering.

Kat

iTrader: (4)

Like I said, depends on who you want to argue with, or did that go over your head?

Dewey316

I strongly doubt your comment was over my head.

So you are saying, that adding weight that is not needed is a good idea?

CheezX

Nobody is trying to start an argument here. Just providing the engineering facts, which just happen to conflict with your opinion.

Kat

iTrader: (4)

To a point and I don't think that "most" people will cry over 8 pounds.


For the weight of the hollow 36mm
https://www.thirdgen.org/techbb2/sho...ht=36mm+weight

At work today I weighed the 34mm soild bar which is 22.8 pounds.

Cheesex Like I said depends on who you want to argue with. There is a few different points of looking at it as you well know and the way I know isn't the right way but makes sense to me.

BTW I am a engineer... Just not for car stuff. Anyone need a puter network?

Kat

JPrevost

Why not measure the torsional stiffness of Steve's bar compared to the stock populer 36mm hollow? That would give you a selling point or tell you that you're wasting time making a solid front bar .
I can personally vouch for not wanting to add any more weight to my front end. Then again I'm a weight freak. If it's not needed it's not there (as in look, radiator support doesn't need all those fasteners ).
An adjustable sway bar would be cake... might propose that to Steve when you get a chance. I'd love to buy a part that's adjustable and not fixed. Tell him to stop making that darn "adjustable" wonder bar and turn it into an adjustable sway bar.

Dewey316

Well put Jon.

Kat... That 8 pounds is significant, remeber sprung v. unsprung weight, and look at the swaybar, part of the weight is unsprung. There are plenty of people who will gripe about 8 lbs of extra unsprung weight.

Now a real selling point, would be to make a bar that is equal or less wieght, and has the more stiffness.

ShiftyCapone

iTrader: (7)

Not to drone on about hollow bars but you can use the following simple exercises to calculate the differences in maximum shear stress due to bending.

r = radius to outer surface
T = applied torque to bar
J = moment of area
Do = outside diameter of bar
Di = inside diameter of bar (hollow bars)
Tmax = maximum shear stress

Tmax = (T*r)/J

For a solid sway bar

J = (pi*d^4)/32

For a hollow sway bar

J = (pi/32)*(Do^4 - Di^4)

Start playing with some numbers and your answer will be clear as to which is stronger. There are reasons, as mentioned above, as to why you would choose one over the other though. Like Dewey and JP I am in favor of the lighter one that just so happens to be stronger. FWIW

Kat

iTrader: (4)

Or you could go on a diet. lol IIRC that "unsprung" weight that gets thrown arround here often, wouldn't that be more or less applied to the actual weight of the a-arm, spring, spindle and whatnot where as the weight of the front sway bar is supported by the frame of the car?

Kat

nape

iTrader: (1)

Nope, half the weight is unsprung because it has one body mount and one mount to the suspension. Think of it in the same way as a rear LCA. Half the weight is unsprung because it has one mount on the body and one on the rear end.

I guess my real question for this thread is though, why not just go to a stiffer rate spring instead of popping for an expensive, heavy sway bar? Not exactly the same effect if you want to be really picky, but it would work and be quite a bit cheaper.

Apeiron

Considerably more than half the weight of a swaybar is in the portion of the bar which is mounted to the body.

Dewey316

Nape,

I think most of the people in this thread are in agreement. People also need to remeber, that bigger is not always better, especialy in swaybars. depending on your ride height, and spring rates, a very small front sway bar, may be needed to balanace the car, in other cases, a bigger may be needed.

nape

iTrader: (1)

True. I withdraw the earlier comment.

Dewey316

Yes, but there is still part of the bar, that is unsprung (i don't have an actual percentage).

My point is the fact, that he is trying to tell us, that a heavier part is better, when a lighter part could do the same job (or as CheezX pointed out, a "better" job.)

Apeiron

Some percentage, yes. The sprung/unspring thing makes no difference, since the hollow bar has less of both anyway.

ME Leigh

Hey i'm glad to see the old T*r/J on here!

ShiftyCapone

iTrader: (7)

Every now and then I bust out an old exercise so that I don't become too far removed from it. This happened to be a perfect refresher

Kat

iTrader: (4)

Is that appiled to the bar tornsonally or straight up and down?

Kat

JPrevost

ME students;
Calculate the needed wall thickness of a 36mm od 12" section of tube to equal the bending stiffness of a 34mm solid bar. (state the value you used for Young's Modulus).

Apeiron

I'd do it, but I'm an EPhys, not an ME, so this is much to practical a task for me.

Lo-tec

Practical real world example from parts removed and replaced on my car when switching from a 32mm solid to a 34mm hollow bar:

32mm solid bar weight 22.0 lbs

34mm hollow bar weight 13.8 lbs

Assuming the weight difference is approximately the same as the difference in the cross sectional area of the bars gives an inner diameter of the hollow bar to be 22.66mm. Inserting into the above formula yields:

J(32mm solid bar) = 102,943.71 mm^4

J(34mm hollow bar) = 105,310.00 mm^4

...which ends up to be a bar that is both 2.30% stiffer and 8.2 lbs lighter (37%) and which, when replaced, performed the same as the heavier solid bar (i.e. didn't notice it was changed).

TheV6jerk

The difference between a GM 36mm Hollow steel bar and a Spohn 34mm Solid CM bar is so minute when it comes to driving comparison. You can not tell the difference.

What is important to note is that the arms of the hollow bar are in fact less unsprung weight and the weight ofthe hollow bar has less polar weight on the nose of the car.

However, the solid bar will not corrode and fail like the hollow ones do over time and especially in bad weather states. Put aftermarket bushings on the factory hollow bar and makeit work harder- that failure will come sooner.

If you can find a new hollow bar, I'd go for it. Otherwise, if its a street car you plan to drive for many years of abuse, the Spohn bar is hard to beat, it is bullet proof.

ME Leigh

Did Dean get banned again? Cool name!

soulbounder

I do believe that is what happened.

(Sorry, I've just been looking for an excuse to use that smiley. )

Here is a simple question. Has anyone plugged the holes in the ends of a GM 36mm bar? The only way it seems that they would corrode and fail is from inside out. You could even put a stem in the end of one side and keep it pressurized if you like.

RBob

iTrader: (1)

Interesting idea. Looking at a hollow GM bar the ends themselves may not be sealed. It looks like thay are just pressed together. The bar I am using has the holes on top, a 90 or 91 Formula bar.

I've thought about inserting/pouring/squirting some motor oil into the bar. Next time I'm under the car I'll probably do that. Can't hurt.

RBob.

TheV6jerk

A bit of trivial for everyone. Did you know that WD40 was developed by the military in order to keep the nukes in the silo's corrosion free? The spray repells and protects the metal missiles from water damage. Hence WD- Water Displacement. It was the 40th formula tested

Spray a little WD40 in there now and then.

Lo-tec

Very interesting. I checked mine after your post, and the holes on mine are indeed on the bottom (where I would guess they should be to drain water). Not asking this question to be a smart a$$, but is it in upside down, or do others have holes up top as yours???

ME Leigh

The holes are supposed to be on the bottom. I'd guess you have yours on upside down. I don't really know why the holes need to be in there. The ends of my hollow bar appeared to be pressed together sealing them. I might go put am silicone over the holes on mine on a hot, dry day.

83 Crossfire TA

iTrader: (2)

Fill it with linseed oil like old airplane frames used to be.

As far as actual stiffness, you can figure out the stiffness of the bar using the equasion that and the weight of the actual bar to figure out the approximate wall thickness. You’ll be surprised.

As far as the weight, I’m sure that I posted it before, but the 36mm bar is the same weight as the posted weight of the 34mm bar.

As far as banning dean… what’s the point if you let him stay under his new name. Dump him as soon as he turns up again enough times and eventually he’ll give up. What did it actually take for him to get banned anyway?

83 Crossfire TA

iTrader: (2)

heh, and you’ve exactly nailed why I keep trying to find a 34mm bar… the setup that I was happiest with had a 32 solid on the front. I think that the 36 hollow bar that most people like is actually too stiff and prefer stiffer springs instead, but have a hard time justifying adding weight to the nose of the car to soften the suspension.

RBob

iTrader: (1)

Sorry, no, bar is on correctly. Vents are on top. Looking at the bar I don't think it would work out too well if bolted in upside down. The arms would hit portions of the body structure.

RBob.