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Topic Review (Newest First)
03-12-2004 07:35 AM
BillyShope Bullet, I feel it's necessary to modify that which I said in an earlier post. On your triangulated links, the front pivot points are very close together. For this reason, I said you had nothing to worry about as far as binding is concerned. Than, cboy posted pictures of his setup. As you can see, his triangulated links are separated, at the back end, by the center section. The further apart the mounting points at the "peak" of the triangulation, the more bind will occur. Cboy has taken care of the problem by using rubber bushings. This is how Detroit takes care of it, too. These kits, however, usually use Heim joints, which are, of course, quite rigid. There's always going to be a little "give," of course, so some binding can be tolerated, even with Heims. Though the Heims are "pretty" pieces of hardware, don't feel that you have to use them. The Ramchargers used rubber bushings on the trailing links of their C/A.

As to why binding occurs: It only takes 3 trailing links and a Panhard to locate an axle. Any more trailing links can cause binding. Your upper links are mounted so close together, at the front, that they're essentially one large triangular link. In fact, if a single Heim could take the loads, it would be ideal to combine the links at the front and use one Heim. (I'm not saying you should do this, for that's a big "if.")

Anyway, this is another good reason for Morrison to show the links parallel in the side view. He doesn't want you breaking Heim joints with excessive deviations from parallel which cause higher binding loads (though still much less than with a conventional 4link).
03-11-2004 03:15 PM
1950bulletnose Thanks all. Something to consider and keep an eye on when the car becomes road worthy. Hopefully I won't have any problems. I've gone backward a couple times with my project and I don't want to go there again. I hope I left enough adjustment if a problem does arise. Again, thanks for all the imput.
03-11-2004 08:04 AM
cboy brainsboy,

Very good info in the prior post. Here's pics of the triangulated setup under my 32 just to give you another perspective. This was totally built for the street not for racing.



03-11-2004 08:03 AM
BillyShope Just tried to check the Morrison site and wasn't able to complete the connection. Don't know if they're having server problems or what.

Anyway, I'm aware that some of these suppliers seem reluctant to discuss this sort of thing. I suspect it's just a matter of maintaining a "neutral" position on some of these issues which, among some racers, are highly controversial. And, I certainly can't blame them for wanting to keep their bottom line healthy.

Why controversial? Well, there are some who actually want a lot of squat. So, if a supplier comes out and says, "Here's how you can avoid all that nasty squat," they might consider the guy incompetent and take their business elsewhere. On the other hand, there are those who want a lot of rise (though there aren't as many).

Why do some want squat? They see the rear end of the car coming down and they think what they're seeing is weight transfer. So, the more they see it coming down, the more weight transfer. But, that's simply not how it works. Weight transfer is a function of acceleration, car weight, wheelbase length, and center of gravity height. Nothing more! Actually, what's happening as the rear starts to come down is that a certain portion of the weight transfer is LOST as the force is applied to pull the car down. But, that which was lost is regained as the car "bottoms out" and starts to return to its upper position. In other words, rear wheel loading oscillates as the car bobs up and down. You get the same oscillation with a "rise" setup, but it starts with an increase in rear wheel loading.

So, as far as I'm concerned, it's best to avoid all that bouncing and keep the rear wheel loading as steady as possible by putting the IC on that line I described. From the pictures, I would say that you might have enough adjustment in the lower links to accomplish this.
03-11-2004 05:40 AM
1950bulletnose BillyShope
I've looked at Art Morrison's (artmorrison.com) setup, and I don't see any difference in his setup to mine other then his housing brackets are on the front of the housing and mine are on the top. His bars appear to be parallel to themsevles and the ground. There's no mention in the kit about squat and I followed the instructions and diagrams to the letter. Geez.........I hope I haven't %$@#$% up'd.
03-11-2004 04:07 AM
BillyShope I thought you had fabbed your links, Bullet. Didn't realize they were a kit. Anyway, if, in side view, your upper and lower links are parallel, both to each other and to the ground, the car will squat miserably on acceleration. This is because that which is called the "instant center" is at infinity.

To determine the location of the instant center (IC), visualize lines through the upper and lower links in the side view. Their intersection point is at the IC. Now, visualize a line passing through the rear tire patch and the intersection of two more lines, one a vertical line through the front tire patch and the other a horizontal line through the center of gravity. If the IC is on this line (the one passing through the rear tire patch), The car will neither squat nor rise. If below, it will squat; above, it will rise.

In accomplishing this, you don't need to worry about suspension link bind. That's why your upper links are triangulated in the kit. When this is done, it's the same as if those two upper links were replaced with a single link at the center (and, of course, a Panhard to locate the axle laterally). And, there's definitely no binding with a 3link, which is why the roundy-round boys like them.

If you're going to use bags in the rear, I would definitely recommend a no squat/no rise setup, as the low rate of the bags will accentuate the squat.
03-10-2004 06:40 PM
1950bulletnose Yo BillyShope,
I was just going back over what you posted. Unless the bars are long ( which in this kit from Air Ride Technologies, they are not ), one can only at best keep the bars level and parallel with the lower bars, any deviation from that would cause the suspension to bind in it's multi functional travel. I think if you look at the pics of the frame again, you'll see that indeed the bars are either level or slightly angled down. I thought it through very carefully and followed the instructions to the letter. The differential travels it's full geometry of motion without any problem and that's a good thing, as the car will be equipped with Air Ride and at times be in the weeds.
03-08-2004 06:21 AM
brainsboy Thanks for all the information guys this helps alot..


Ben
03-05-2004 12:09 PM
astroracer Kudo's Bullet... Nice work.
The "hopping" you are seeing is a result of running a locker or spool in the rear diff. It's caused by the inner and outer tires trying to turn at different RPMS around the locked axle. The inside tire tends to skip trying to catch up with the faster turning outside tire.
Mark
03-05-2004 12:00 PM
1950bulletnose Yes, I did too make a mistake, thanks for the reposting of my URL. Also thank you for your encouraging comments.

The tri-angulated 4 link on my project is parallal and straight. There's plenty of adjustment there when the time comes to get the pinion angle right. The rearend at this point is held in that position by welded bars which I'm going to cut off and remedy soon with a couple strut bars where the air bags mount. I'll also make a couple strut arms for the front so the car can be pushed around the shop. I've put away the air bags until the car is in it's final assembly. I don't want to burn or punch a hole in them. The frame is not totally finished yet as I still have a driveshaft loop to weld in the rear crossmember as well as cross bracing that member for strength. The front bags still have the upper mounts to be welded on. It's my first attempt at building a frame and I think I've done ok. I did get help from a buddy who builds race cars. I took plenty of time to think it through and to take lots of measurements from my old frame.

Still have a long road ahead before it's finished.
03-05-2004 11:09 AM
BillyShope That's a great site, Bullet! If you don't mind, I'm going to retype it so others can see it. Afraid you had a typo in your post:

http://www.angelfire.com/super/1950bulletnose

Now, I just hope I didn't add another error.

I had a '54 hardtop. Although, except for the body and about 3 feet of frame rails, there wasn't much left that was Studebaker. That hardtop was a beautiful car, though.

Anyway, yes, the triangulated setup will not bind while cornering. And, you don't need a Panhard, which is why it was used in production cars (saved some production costs). My only concern was that it appears that the upper arms are angling up from the rear. Hard to tell from the pictures, though. And, the axle might not have been at ride height. If they are, though, this would mean you're going to be getting a lot of squat on acceleration. If you'll look at the cars from Detroit with this setup, you'll see that the upper arms are angling down.

I don't think I'd blame the parallel 4link for the "hop" you've seen on cornering. There's a lot of things that could cause it. If the links are truly parallel, there will be no binding and the car will corner like your triangulated setup. Don't misunderstand me! I'm not saying you should have used a 4link. Definitely not. You've got a beautiful setup for a street car. For that matter, it should do quite well at the strip, so long as the squat is not excessive. It does not, however, offer the adjustability which some would desire.

Good work!
03-05-2004 09:46 AM
1950bulletnose If you want to avoid any binding at all in a street application, a Tri-Angulated 4 Link is the only way to go. Pro Street cars with parallel 4 link or ladder bar suspensions tend to hop around a corner because there is no give in the roll of the car when cornering. I found this out with my Studebaker Resto-Rod and scraped the Ladder Bars in favor of a Tri-Angulated 4 Link with Air Ride. Project pics at http://www.angelfire.cim/super/1950bulletnose
03-04-2004 11:15 AM
astroracer That's some very good info Billy. I had never considered running the bars at different angles side to side... Your analysis makes perfect sense and it should work just fine...
I wish I had talked to you before I started my Astro van project. I have decided to go with leaf springs and home made Caltracs for my rear suspension just because I couldn't come up with a 4 link design that would work both in a straight line AND a cornering situation...
Ben,
Here is some more info from Alston's site. http://www.cachassisworks.com/techtips.htm
This will give you some good info also and if you look at it from Billy's point of view you should be able to come up with a workable design...
Mark
03-04-2004 09:56 AM
BillyShope Yeah, that RPM site is pretty much for the roundy-rounders.

You can get a little drag info at some of the other manufacturers' sites, but not all of it is good. In other words, even the people that make 4links can steer you wrong.

For instance, they'll tell you that, if you drive the car on the streets, the links (upper and lower) should be parallel. This much is true. Unless the axle brackets...on at least one side...are free to rotate on the housing (a "floating" mount), a non-parallel link arrangement will result in a "binding" of the linkage as the car corners. This is because the right side link pair is trying to rotate the housing in one direction while the left side link pair is trying to rotate it in the other. But, if the pivot point is at infinity (parallel links), no binding will occur.

But, they'll usually go on to say that the links should also be parallel to the ground for the street. This is NOT true! This will yield excessive squat (of the rear of the car) as you accelerate. If the parallel link pairs are angled up from the rear, you can lessen or eliminate the squat and still avoid binding.

At the strip, you can find all kinds of non-parallel arrangements being used by racers. So long as you remember to return to the parallel arrangement before driving home, those Heim joints and links can take quite a bit of punishment.

There is, however, a little-known "trick" that can be used which works effectively on both the street and at the strip. On the street, it allows you to drive hard through the corners without worrying about binding, and, at the strip, it cancels driveshaft torque, allowing equal rear tire loading as you launch. In other words, it's "set it and forget it."

I mentioned angling up the parallel bars to reduce squat. If those links are set at an angle, to the strip surface, which has a tangent equal to the center of gravity height divided by the wheelbase, the squat is entirely eliminated. Any angle greater than that will cause the rear of the car to rise on acceleration. So, here's the trick: Set the parallel right side link pair to an angle 5 degrees greater than the angle I've just described and set the parallel left side link pair to an angle 5 degrees less. Stop and think about what this will do. The right side wants to rise (slightly) and the left side wants to squat. The net result will be an increased loading of the right rear tire which is in opposition to the unloading caused by driveshaft torque. The 5 degrees is, of course, a starting point. You might want a little more or a little less, but, with the average car, that will get you pretty close to full cancellation of the driveshaft torque.

As the RPM site points out, any upward angling of the parallel link pairs will result in a certain amount of that which is called "roll oversteer." That rear axle assembly is rotated, when you go through a turn, in a manner similar to the front axle of the push kart you made as a kid. But, here's something to remember about roll understeer/oversteer (and many roundy-rounders don't even know this): The roll U/O DOES NOT CHANGE THE WHEEL LOADINGS. In other words, the car is able to negotiate a given curve at the same speed, with or without the roll U/O. All the roll U/O does is change the amount of steering wheel angle required. The psychological effect is, however, very strong and it's often very difficult to convince a driver that the basic handling hasn't been changed when roll U/O is introduced.
03-04-2004 08:37 AM
astroracer Here is a very informative site...
http://www.rpmnet.com/techart/4link.shtml
granted it is circle track oriented but you will get the idea and pick up some knowledge...
Mark
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