i read the threads on triangulated 4-links and i got some information that was useful, but im not 100% sure so i thought i would ask your opinion before i started welding things.
i put the lower links parallel to the ground and the frame at ride height, they are about 3' long. the upper links are ~ 15 degrees down and 45 degrees out (from the top) and they are 2' long.
if you need any more information, just ask me.
remember that this is my first time doing this so take it easy and explain things as if i had down syndrome.:drool: here are a couple pictures to give you a better understanding of my setup.
The following is a portion of one of my posts from a previous thread:
I would also add that, when it comes to the angles (as viewed from the side), pay attention to the OEM setups and NOT to the aftermarket pieces. I saw pictures of one aftermarket arrangement which appeared to have the IC behind the axle, which would mean SEVERE squat on launch. You don't want that. If you want to eliminate squat or rise entirely, arrange the links so that lines through them, as viewed from the side, intersect on a line which passes through the rear tire patch and has a slope equal to the CG height divided by the wheelbase. If the intersection is above this line, the car will rise on launch; if below, squat. It's not necessary for either pair (top or bottom) to be level.
i dont know what you mean when you say
"arrange the links so that the lines through them intersect on a line which passes throught the rear tire patch and has a slope equal to the CG height divided by the wheelbase"
In the side view, visualize a horizontal line through the center of gravity and a vertical line through the front tire patch. Then, a line...called the "no squat/no rise line"...passing through the intersection of these two lines and the rear tire patch.
Finally, visualize lines passing through the centerlines of your links. There will be an upper line (through the upper two links) and a lower line (through the lower two links). If you don't want the car to squat or rise, arrange the links so that the intersection of the upper line and the lower line falls on the no squat/no rise line. If you want it to rise, put the intersection above the line; squat, below the line.
I think you misunderstood where the front tire patch is located. It is (I believe) a vertical line perpendicular to the ground that passes thru the center of the front tire. Conversely the rear tire patch is the same thing except it goes thru the center of the rear tire.
The center of gravity line is for the most part at some height above and parallel to the ground. I'm not sure how you would determine this.
In Billy Shopes example, I think he is under the impression that you have a non-parallel, unequal length four bar setup.
I am under the impression that you are wanting to use a triangulated four bar setup. If this is the case, the lower bars would be parallel to the ground as would the inner "V" bars. The inner bars act as stabilizers to reduce side to side movement as well as locate the rear end. The lower bars locate the rear end.
I think I also nead some clarification from Billy Shope or others to fully understand.
Here is a picture of my recently constructed four bar install. I think your lower bars look really long. In theory the longer the better as far as pinion angle and things go. But as you make the bars longers they bend easier too. I think what Billy shope is trying to say is make sure your bars intersection point is at least in front of the axle. If you look at your setup from the side view and visualize your bars extending in lenght until they intersect, where is the intersection point. Is this point somewhere in front or behind the rear axle? It should be in front of the rear axle and ideally it should lie on or as close as possible to the above mentioned anti dive/squat line.
Whether the links are triangulated (to eliminate the necessity for a Panhard) or "straight," the comments I made concerning the lines visualized in the side view still apply.
There is nothing "magic" about either link line being parallel to the ground. The important matter is their intersection and its relationship to the no squat/no rise line. (If both upper and lower link lines are parallel to the ground, the car will squat severely on launch.)
When someone refers to a 4link suspension, I think of a typical competition style setup with 4 independently adjustable straight links. Reference to a 4bar suspension brings to mind an arrangement where the bar pair, on each side, is constrained by brackets at each end so that the bars are always parallel. The 4link provides more adjustability but is more likely to cause binding problems when driven on the street. The 4bar does not bind and is quite at home on the street.
The triangulated 4link shown in process does not appear to be sufficiently triangulated. That is to say, the ends of the links forming the bottom of the "V" are too far apart. You might get by with this if you replace the Heims with large rubber bushings. Even if you place the two ends as close together as possible, I still think rubber bushings are a wise choice if you're going to do a lot of street driving.
I think you are talking about my suspension when you refer to the one that is not sufficiently triangulated. The ends of the links don't have heims, I am using Poly bushings. I was a little concered about the angle of the upper bars, but after getting everything welded in I think it will work fine. I attatched another picture that shows more of an overhead view. I know it is best to be at 45 degrees, however due to my rear end configuration (8.8 Ford) with the cast center section I really can't get the mounting points any closer together. The only way I could have made the angle closer to 45 would have been to make the upper bars about 30% shorter. I didn't want my upper and lower bars to have that much difference in length. The anle of the bars now is almost 40 degrees now and I think it will work. All of my "side Geometry calculates out very good the way it is, but if you don't think my overhead angles will work please comment. It's not to late to fix a mistake.
Yes, it's clear now that those aren't Heims. Well, it's possible that you'll never experience any trouble with the plastic bushings. I think it might be worthwhile, though, to give a bit more thought to a bracket which would span the center section and provide the pickup point for the bottom of the "V." Yes, it's quite a bit more complication, but you'd never have to think about it again.
Johnsongrass1, that's a pretty picture, but I wish the guy who did it hadn't been so stingy with his words. I assume the vertical line passes through the CG. This would mean the bottom sloped line...I think he calls it the "normal" line...might be the "no squat/no rise" line to which I was referring. That would seem to jibe with his mentioning the indicated instant center is associated with "rise." I wish I could edit it to show the front tire and its relationship.
I thought a side view would be benificial to the conversation.
What happens if you move the upper link to a degree that the imaginary line running through the upper link and lower link never intersect? Does that cause extreme amount or rise? Even to the point that the rear spring does nothing?
Billy,
you seem pretty to know and understand quite a bit about 4link setups, Is there a book or something that shows how to design suspensions in detail? I have a book on hot rod chassis building but all it does is recomend aftermarket stuff.
thanks
That is a spreadsheet that I made that will calculate many of the variables for you on any triangulated 4-link (BillyShope I saved it as a excel 95 file just for you:thumbup: )
You can find all the info you could want in Race Car Vehicle Dynamics by Milliken & Milliken. I think something better to start with would be ANYTHING by Carroll Smith, Chassis Engineering by Adams, and I'm sure there are many other good books I'm leaving out (I have a stack a few feet tall). I don't know why BillyShope hasen't written one yet:mwink:
The book Triaged mentions (RCVD by the Millikens) is that which I chose as text when I was teaching this stuff to engineering students. I didn't know the Millikens when this book was being written, but I did contribute to the student workbook which was published later and I hope that they might consult with me if they ever add chapters on drag and oval racing in a later revision. But, I would never consider myself worthy of writing anything other than an occasional article when men like the Millikens are around! Bill is nearly a centenarian, but I'll never know that much if I live to be 200. Yes, Puhn and Smith offer valuable and accurate information in their books (and they're considerably cheaper), but RCVD is commonly referred to as the authoritative reference book.
Joshsongrass1, the suspension springs are removed from the picture only when there is no squat or rise. With squat or rise, the chassis moves relative to the axle assembly, meaning forces are transmitted through the springs.
When the link pairs are parallel, the instant center is at infinity. (Parallel lines meet at infinity.) So, if the link pair is parallel to the no squat/no rise line, the car will not squat or rise. If the link pair is horizontal to the ground, the car will squat excessively.
Triaged, thanks for the copy usable by my ancient version of Excel. I'll take a look at it later and email you.
I am also attempting my first four link. Actually, this is the first chassis work I've done, so I made mine adjustable. I can change the angles if needed. This is the first time I've tried to post a picture here, hope it works. I don't know if this will help. Good Luck Ed.
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