FindlaySpeedMan New Reader
June 6, 2009 3:50 a.m.

Like the topic says, can you make your own anti-roll bar out of pipe. I've been thinking about LeMons for no good reason lately. I've seen bars like this one before-

sway-2

Which makes me wonder if I can take a piece of any pipe, make end pieces out of scrap steel plate, do or have done some quality welding, and viola, instant roll bar for almost nothing. I'm imagining using this to put roll control in the back of some old beast of a wagon, so I can just mount the thing above the live axle.

Would that even work? Or would the bar need to be special steel? Could I make something that would at least work, if not well, or is there something to this concept that I'm missing? Would a regular piece of steel pipe just snap?

ddavidv SuperDork
June 6, 2009 6:04 a.m.

I'm no engineer, but it's all about the torsional bending resistance. A solid piece of 'pipe' is not going to flex much. You'll want a little bit of flex or the thing will be too rigid. If you can't achieve flex with the piping it will have to take place on the end links. Another issue then is if the stresses and lack of flex are too much, the end links may fail.

RedS13Coupe Reader
June 6, 2009 6:37 a.m.
ddavidv wrote: I'm no engineer, but it's all about the torsional bending resistance. A solid piece of 'pipe' is not going to flex much. You'll want a little bit of flex or the thing will be too rigid. If you can't achieve flex with the piping it will have to take place on the end links. Another issue then is if the stresses and lack of flex are too much, the end links may fail.

Some of that could be accounted for by the length of the lever arm.

I would bet that for real applications special steels are used with special heat treatments.

For something like LeMons I would try and find what metal tubes are available and what they are made out of... then google them and look for the one with the lowest modulus of rigidity/shear modulus and adjust the lever arm to make it work

You could also try heating the crap out of it and letting it cool slowly to see if you couldn't make it any softer if you really wanted...

ncjay New Reader
June 6, 2009 6:56 a.m.

A sway bar needs to be able to twist, while not becoming permanently distorted. I would guess that a normal mild steel pipe would probably twist a few times and then experience metal fatigue. Maybe if the pipe wall was thick enough, it could work. It would probably have to be cold rolled seamless tubing to even have a chance. Getting the right hardness would be a shot in the dark.

ignorant SuperDork
June 6, 2009 7:02 a.m.

Most pipe is made by forming sheet into a tube and welding. The weld seam will be much more brittle than the surrounding metal.

YaNi Reader
June 6, 2009 7:14 a.m.
ignorant wrote: Most pipe is made by forming sheet into a tube and welding. The weld seam will be much more brittle than the surrounding metal.

Correct. You will need seamless tubing, which is much more expensive. I built my sway bar with cold rolled steel bar stock. The sway bar can twist more than you would think; it will bend before it shears.

Jensenman SuperDork
June 6, 2009 7:18 a.m.

An anti roll bar has to be a lot like spring steel, it can be done in the back yard so to speak but the chances of getting it right the first time are not real good. They go for next to nothing in junkyards, I'd go that route. Find something that's the right width (or at least close) and then fab up brackets. For instance, I found a rear sway bar from a Jeep Wrangler which is almost a perfect fit under the rear of the Jensenator.

YaNi Reader
June 6, 2009 8:03 a.m.

It isn't hard at all to build your own sway bar. There are TONS of applications that weren't designed for sway bars, so something needs to be custom fabricated.

These calculations will determine the allowable angle of twist of the center section of the sway bar before it deforms. Basic chug and plug. You can determine what material you will need to obtain the necessary angle of twist for the suspension to travel. You could use some algebra and use the equation to determine the necessary shear strength. Its 9am on a Saturday, so your on your own.

This is a screenshot of a suspension calculator, which can be found here.

I have more pics here.

It ain't rocket science...

Trans_Maro Reader
June 6, 2009 8:44 a.m.
slantvaliant Reader
June 6, 2009 12:34 p.m.

What about Mopar A-body torsion bars? Nice hex ends, available from about 0.8" to over 1" OD, spring rates are available somewhere ...

RedS13Coupe Reader
June 6, 2009 3:07 p.m.
Trans_Maro wrote: How 'bout one of these: http://www.speedwaymotors.com/Universal-Rear-Sway-Bar-Kit,4053.html Shawn

Price seems steep for a LeMons car?

Trans_Maro Reader
June 6, 2009 4:52 p.m.

So copy it with available materials.

Shawn

RedS13Coupe Reader
June 6, 2009 6:22 p.m.
Trans_Maro wrote: So copy it with available materials. Shawn

Thats pretty much what this thread is asking about

96DXCivic Reader
June 6, 2009 6:37 p.m.

Race Tech recommends either 080M40 steel or hydraulic tubing for sway bars in the November 2008 edition.

Schmidlap New Reader
June 6, 2009 7:22 p.m.
ncjay wrote: I would guess that a normal mild steel pipe would probably twist a few times and then experience metal fatigue.

Bingo.

MikeSVO Reader
June 6, 2009 7:28 p.m.
FindlaySpeedMan wrote: I've seen bars like this one before- sway-2 Which makes me wonder if I can take a piece of any pipe, make end pieces out of scrap steel plate,

^^^ That up there looks like a UPR anti-roll bar, which is not supposed to flex.

thatsnowinnebago HalfDork
June 6, 2009 11:51 p.m.

I've the stock front swaybar from an 87 toyota 4x4 pickup if you want it for the cost of shipping

FindlaySpeedMan New Reader
June 7, 2009 5:56 a.m.

First, I'm sorry if I got anybody real excited. I'm just bench racing here, and wondering if my ideas are clever or stupid. I currently lack the car, tow vehicle, trailer, and money to go to LeMons, and my skills as a con-artist are pitiful. Maybe I'll make some money off my website (ha!) and then I can start getting real.

MikeSVO-I nabbed that photo off of a drag racing site. Googling UPR shows me you're probably right. I've seen such bars in that application before, and that's where I got my brainstorm. I honestly don't know if they operate the same as normal bars, but since drag cars only go straight, I wouldn't be surprised if they don't.

Dammit, YaNi, I'm like an English major without the degree. That E36 M3 looks like rocket science to me. I did, however, pass high school calculus once upon a time. So I can probably crunch my way through that.

And yeah, the whole real point of this post is about substituting smarts for money. If I can figure out what kind of materials I need to make a swaybar, then maybe I can fish it out of a dumpster somewhere.

Keep the commentary coming. I'm a bench-racing windbag, but there's probably some kid out there with more gumption than me who can put this discussion to use.

RossD Reader
June 7, 2009 11:30 a.m.

just go grab a torsion bar out of a late model gm truck (full size/s10/colorado) or like some else said an A body mopar. or old beatles, 911s... I'm sure theres more too.

MikeSVO Reader
June 7, 2009 11:35 a.m.

I'm more of a drag racer right now, just because going straight very quickly is really cheap compared to going straight and turning and stopping very quickly.

For that UPR bar, you'd weld the plates that hold the fat bar in between the frame rails, parallel to the axle tubes in the back of a Fox Mustang (and maybe other cars, I dunno). Then you weld the little tabs to the axle tubes. When you connect all that stuff together, it keeps the rear axle and the body parallel all the time because the fat bar doesn't flex. It can still go up and down, but can't lean (twist) at all. You're really NOT supposed to have that thing connected on the street, but at the track, it keeps everything right where it needs to be.

The_Jed New Reader
June 7, 2009 12:10 p.m.
FindlaySpeedMan wrote: Dammit, YaNi, I'm like an English major without the degree. That E36 M3 looks like rocket science to me. I did, however, pass high school calculus once upon a time. So I can probably crunch my way through that.

Don't sell yourself short,Findlay.Engineers with degrees need calculators just as much as those without degrees need them.In my opinion innovative and abstract thought are the earmarks of those with a talent for engineering,not necessarily diplomas.

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