crossover 4 link

I had someone ask me about doing a 4 link with the upper and lower bars both in triangulation oposite directions to eachother. It would basicly look like 2 x's if viewed from above. I had to admit that I had no idea weather it would work or not. I can't see any performance gains from orienting a setup like that, it would just be for visual appeal I guess. I haven't had time to do a paper doll mockup on it yet but I figured I would check out your thoughts in the mean time. Thanx for your time and keep up the good work.

In a situation like that, you can end up with some interesting roll-steer. On a triangulated link system, the roll center is figured by finding the instant center of the upper bars and do the same for the lower bars, then take those two points and draw a line between them. That line is the roll-axis of the rearend. On a typical triangulated 4-link the upper bars are triangulated as much as possible so the instant center is right there at the point where the bars come together and the lower bars are parallel to each other in that case the i.c. is considered infinite, so the roll center is at the point of the triangulated bars. By triangulating both uppers and lowers, you can see that the rearend will rotate at an angle around an interesting roll-axis.

Make sense?

make drawings of this stuff.... I'm lost

I don't know what to tell you there. Those would be some complicated drawings. When calculating the instant center of your 4-link you would just use a side view, but to calculate the roll-axis of the rear suspension, you would need to use a side and a top view and understand how to bring them both together.

Let me try to simplify this.

If you were to build a wishbone 3-link, the single point of the wishbone os the roll center. The rearend swings from side to side around that single point. If you were to build the same type of thing, where the upper wishbone came to a single point at the frame (the front mount) but run a wishbone as a lower link as well and run the single point on the rearend (the rear mount.) The rearend could only pivot on an axis set by those two wishbone points.

Does that make more sense?

Makes sense to me.

I see this kind of setup on a lot of 4WD stuff. Quite a lot really. Is there any reason they are running them, as opposed to us?

I could see how that might work good on a "trail rig" but not at highway speeds.

Thanks for your input Max. I was thinking along similar lines but just wasn't sure without mocking it up and seeing it work. I'm a really visual/ hands on kind of a learner. Keep up the good work.

They built a trail rig on Extreme 4x4 with a double triangulated 4 link. I had crazy articulation.

In a slow rolling type situation it would be an advantege because the rearend wouldn't swing from side to side from the single point of the wish bone. It would pivot through the center of the rearend. The roll-steer that it generated would be negligible(sp?)