Rear suspension question

When running a 4 link I'm to understand that the idea is to get the lowers parallel at ride height and have the uppers angle down enough so that the imaginary line to create "instant center" is roundabouts the front bumper, right? For easy sake, if I was running a wishbone upper bar and I had my single pivot on the axle, the bars to the other two points would be lower, right? So what is the object when running the wishbone in the other direction, meaning the single pivot on say an xmember for the driveshaft and the two points on the outskirts of the axle tube? Obviously the two link points on the axle tube are lower than the front single pivot point. I'm just confused on how to figure out the right angle for an upper bar set up where the single link point is on the xmember. My understanding is that it should be close to parallel which would make it similar to running a parallel 4 link except that your lateral limiter is basically the triangulation of the wishbone, for example. I'd love to hear some input from some of the great fabricators on here. Thanks for reading guys!

Nobody?

No matter which way the wishbone is facing, you want it to be angled slightly down in the front to make your instant center. If placing the legs on the axle tubes makes the front too high then you need to either lower the crossmember mounting point, or get taller tabs for the axle tubes. Parallel is also ok but you def dont want it pointing up.

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AVTekk said:

No matter which way the wishbone is facing, you want it to be angled slightly down in the front to make your instant center. If placing the legs on the axle tubes makes the front too high then you need to either lower the crossmember mounting point, or get taller tabs for the axle tubes. Parallel is also ok but you def dont want it pointing up.

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^^^Dave's right on!

Same concept, just not a wish bone. I had to redo mine because I didn't angle the upper bars down enough. I also corrected my instant center by raising my lower bars front mounting point up. I never had it explained to me this way, but the verticle distance between your front mounting points should be less then the verticle distance between your rear mounting points.

You make your instant center where you want the 4 link "lift" the truck under power. Alot of drag cars are set up with the instant center where the engine block and tranny bolt together.

Thanks guys, that helps. Nathan, that's what im talking about, I was just using the wishbone to explain things easier. I had no idea about the mounting points. That's good info. Thanks Dave, makes good sense to me now. I am just trying to understand everything I can about suspensions, shot is interesting...lol. Is there a general degree that the triangulation of your upper bars should be? Thanks for the info and pics guys.

Edited: 4/25/2011 6:12:55 PM by UnusualFabrication

The suggestions listed are all general guidelines for a street driven vehicle. Without diving deep into rear suspension theory (IC, COG, RC, anti-squat) these settings will get you ballpark. The triangulated uppers ideally should be 45 degrees to the chassis (90 degrees to each other). Now in most cases you can't get 45 deg so you'll have to work with the space you have and adjust it accordingly.

Here you go... obviously you would need to adjust for ride height as this example is a lot higher than an air bagged truck would be, but same concept.

I get that these are general guidelines, but that's what I'm lookin' for. I'm currently reading Chassis Engineering so I'm familiar with anti-squat, roll center, etc. Plus I've read most every article or post on here written about suspensions and link setups and the like! Just tryin' to learn and absorb as much about suspension as I can. If anyone knows of any other good reads let me know. However, no matter how much I read, sometimes having experienced builders explain things tends to help. Thanks again for all the input.