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Old 10-02-2005, 09:25 PM
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Triangular 4 Bar Link

Does Anyone Know What The Wall Thickness Is On 1" Steel Pipe Used For 4 Bar Link. I Not Sure If I Want To Use Parallel Leaf Springs Or 4 Link. If I Find The Right Wall Thickness I May Like To Build My Own. Thanks For Replys. Onegalonly

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Old 10-03-2005, 10:38 AM
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The answer is: "It depends".

How far off the ground will you put the lower links?
How long will they be?
What is the intended use?
How much will the car weigh?

The uppers don't have to be anywhere near as big/thick as the lowers.

Without knowing anything else about your car I would say 1.5" OD x 0.188" wall mild steel for the lowers and 1" OD x 0.120" wall for the uppers....and yes those are on the conservative side.
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Old 10-03-2005, 01:24 PM
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When I consider the loads imposed while using a good set of drag slicks, I tend to be very, VERY conservative! Why not 2 inch OD by 1/4 wall for all the links? That's only 2 pounds per foot more than 1.5 by 3/16ths. You're not building a Formula One car. Those few extra pounds will never be noticed.

And, those Heim joints might look "purty," but I'd go with the rubber-lined bushings used in the leaf spring eyes and some sturdy brackets.

These are critical parts and it simply doesn't make sense to pretend you're Colin Chapman designing a new Lotus.
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Old 10-03-2005, 01:42 PM
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A couple of things I see here...
"Pipe" is not used in automotive suspension applications. D.O.M. steel "Tubing" is. 1 1/4 O.D. x .188 wall is pretty much a normal size for most hardcore drag suspensions arms. Of course these drag suspensions aren't subjected to the cornering and pothole forces that a normal street suspension sees everyday.
Do you have all of the suspension points required to build a 4 link suspension that will work? If you can't design a suspension that will work you should probably stick with the leaf springs...
Look here, do a few searches and learn a bit about the suspension you want to design.
http://www.cachassisworks.com/cac_techtips.html
If you look here you will see some basic prices for the higher grade rod ends and 4 link kits available...
https://www.cachassisworks.com/iwwid...LINKS?COMP=CAC

Designing a 4 link is MUCH more complicated then just welding some parts together and throwing them in the car... Especially if you want them to work.

Last edited by astroracer; 10-03-2005 at 01:47 PM.
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Old 10-03-2005, 02:39 PM
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Quote:
Originally Posted by BillyShope
When I consider the loads imposed while using a good set of drag slicks, I tend to be very, VERY conservative! Why not 2 inch OD by 1/4 wall for all the links?
By my guesses that works out to about 25-30g's of load. Is that how far you would go? That would put the link strength just over the double shear strength of a grade-8 9/16" bolt.

In the fictions example I worked out (3000# car lower links 6" off ground) a 1.5" x 0.188" wall tube would be at about 17g's at yield. It should also be just enough to withstand a close encounter of the floor jack kind (given a link of 24" or less).

In the same example Competition Engineering links (1.375" x 0.095" chrome-moly) would be at yield at just over 10g's (or about 23,000#).

Is the 25-30g range where things should be designed?
Comments on the Competition Engineering setup?
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Old 10-03-2005, 05:49 PM
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A few years ago, I was working on a magazine article with the Hot Rod tech editor and a young man with a Camaro. I had talked the Camaro owner into removing one link from his 4link so that the remaining 3 could be adjusted to provide equal rear tire loading during launch. (This trick was originally employed by Jaguar on their early C-Types.) Like an idiot, I didn't bother to calculate the loads and stresses that would be imposed on the remaining links. The car broke while the owner was testing on the street. Fortunately, noone was injured and there was minimal damage to the car. But, to say that I've been "snakebit" would be quite accurate.

If you design "by the book," you are supposed to include things like shock load and safety factors. And, when you figure in friction coefficients over 2 and a reasonable design stress, you do, indeed, end up with "pipe" and not thin wall tubing. Few would buy a car from Detroit if the rear axle was located with one inch OD tubing.

So, what about "what everybody else is running"? Unfortunately, some suppliers seem to go by the design rule: Reduce the size until it breaks and then increase it by 10%. Yes, that pipe I recommended was a bit heavy (okay, more than a bit), but I wanted to get across the idea that, even with that much steel, the weight penalty is nothing to worry about. Most drivers could afford to lose that much exta weight. They'd live longer and they'd enjoy those extra years without the scars from an unnecessary accident. If you're going to err, always err on the side of safety. It's better to have others laugh at your sewer pipe links than have to explain to a young wife and her children why their husband and father is no longer with them. (And that was the nightmare that plagued me after that incident with the young man and his Camaro.)

Although I can't prove it, I suspect that more Heim joints fail than tubing. After a failure, however, it's often difficult to determine the order of failure.

Last edited by BillyShope; 10-03-2005 at 05:55 PM.
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Old 12-21-2005, 12:04 PM
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[QUOTE=BillyShope]A few years ago, I was working on a magazine article with the Hot Rod tech editor and a young man with a Camaro. I had talked the Camaro owner into removing one link from his 4link so that the remaining 3 could be adjusted to provide equal rear tire loading during launch. (This trick was originally employed by Jaguar on their early C-Types.) Like an idiot, I didn't bother to calculate the loads and stresses that would be imposed on the remaining links. The car broke while the owner was testing on the street. Fortunately, noone was injured and there was minimal damage to the car. But, to say that I've been "snakebit" would be quite accurate.

have you ever heard of a three link suspension just wondered if that would help with the adjustment you were talking about here like i said earlier 90 percent of my suspension knowledge is dirt track based if this could work id like to know how
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Old 12-21-2005, 03:38 PM
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As far as that Camaro was concerned, the setup was OK, but the components were simply not strong enough. As I've mentioned in other threads here, the last successful RWD beam axle sports/racing car from a major manufacturer was the early C-Type from Jaguar. This had 2 symmetrically positioned lower links and a single upper link offset to the right to cancel driveshaft torque. You oval racers have been using 3links for a long time, but, in your case, it's better to have the upper link offset to the left. Some racers have gone so far as to have multiple mounting points for the single link and use this as a tuning tool.

The single link can be either above or below the symmetrical links. With a tubbed drag car, the lower position is usually the more convenient. I believe I provided the drag version setup equations in at least one thread here.
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Old 12-22-2005, 06:57 AM
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Billy not only do we use 3 links, we also confuse the issue with choices between spring loaded,rubber bushed or solid upper links.Then just for the heck of it remove the pullbar(upper link) replace it with a spring loaded lift bar .This stuff will keep you up all winter trying to hook up 8 inch tires on dirt with 550-650 h.p.
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Old 12-22-2005, 08:48 AM
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Yeah, I'm aware of all that nonsense and I'm still in favor of the KISS principle and the hiring of a driver smart enough to know when to get off the throttle.
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Old 12-22-2005, 09:08 AM
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True but my wife always says if you'll get in one of these you have already proved ya ain't to smart.I guess sane smart people don't spend bunches of money to go in circles.
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Old 12-22-2005, 12:15 PM
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I certainly did not intend to denigrate the oval racer! It's just that I consider the items you mentioned to be "gimmicks" and that the simplest design is usually the best.
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Old 12-22-2005, 01:37 PM
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no offense taken, just repeating some of my wifes favorite saying's, usually said after I drag home a new car or parts.The one that really get's her goat is when I say something is cheap at twice the price, she knows when I say that I probably spent as much on go fast stuff as she did shopping.Any how on a serious note the use of spring loaded pull bars is being hotly debated,some contend the spring will absorb the tourque reaction and soften the hit on the tires,others say that an inch of travel before the spring goes solid and the tourque absorbtion is minimal at best. I would welcome your opinion on this subject as I am currently considering changing from a mono/coil setup to 3 link.
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Old 12-22-2005, 04:54 PM
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Something to consider: Does GM, with millions of dollars to spend on design, development, and testing, use torque absorption devices on their Le Mans Corvettes?
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Old 12-23-2005, 07:58 AM
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exellent point.
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