Hey guys what are the basics for setting up a triangulated 4 bar rear end? Never done it and need to in the current build. A Channeled A Coupe is that helps
Here's the theory: extend the axes of the angled bars to their intersection. Now construct a line from that intersection parallel to the other two bars (they should be parallel to one another). Your roll centre is where that line hits the vertical plane of the axle. You'd conventionally want it somewhere between the ground and the bottom of the rearend pumpkin - though there are other views. The intersection of the plane of the angled bars and the plane of the parallel bars defines the effective swing-arm pivot in the side elevation. You want that near the car's centre of gravity - and unlike a four-link with Panhard you can set it up that way without binding. Keep in mind that all the geometry changes as soon as there's any suspension movement. You'll have to think how all these defining points move in response to bump and roll movements. Generally, keep the bars long and the geometry won't change too radically.
Lots of good info on this site. Even if they are specifically talking about a drag suspension, you can apply the basic theories. http://www.baselinesuspensions.com/info/Launching_A_Drag_Car.htm
That's a useful article, thanks ThePuck! The beauty of a TFL is that it's possible, at least in theory, to optimize it for launch and cornering performance.
So guys just so I have this right do all the bars need to be pararell when the suspension is at a nuetral setting?
No, the respective planes of the upper and lower bars need to converge somewhere forward of the axle, like on a race 4-bar. That convergence is the instant centre, the pivot around which the effective swing-arm swings. On a conventional 4-bar that arrangement puts stresses into the bars when the suspension is in roll; with a TFL it doesn't, as the link length discrepancies are translated into rotational displacements. The site linked to above gives the neutral line as from the rear contact patch to a point at CG height in the vertical plane of the front axle. I've heard other definitions, and I'm not sure this one is right. Some have the neutral line from the contact patch to the CG. That always made sense to me, as the car's sprung m*** as a body would want to rotate around the CG. I'm still trying to get my head around it. I think you'll be right if you place your instant centre a short distance below the CG. See how it hooks, then adjust it up or down as necessary. That's a good reason to build some adjustability into the system.
the craftsmanship is nice on this frame, but why would any one need something that strong? That design could be used under a car hauler. Don't get me wrong I'm not bashed it , it looks great , I just think it's over kill. I'd like to see the rest of it...
It's well executed, and if the end result is very low-slung the geometry seems fine. If the car has a more conventional CG height the instant centre might be a bit low. It might unload the rear tyres. Raising the attachment points to the frame should fix that. The roll centre is quite high, though, so any attempt to dial out oversteer has limited scope. You could lose all the rear roll stiffness and still have more weight transfer than you want at the back. The fix there would be to reverse the upper bars so the wide base is on the axle and the narrow base is on a crossmember attached to the frame. That'd be better than adding front roll stiffness.
This is how i set mine up. The lower bars are parallel to the ground and the top ones are on a slight angle down in the front. The bars are about the same length. Not sure about the angle, just went with what worked with the rest. I tacked the rearend to the frame with a 4" peice between to keep it place while i was doing it. Have been driving it for 3 years now and has worked good, very little side movement. Only got a bit more than 1" between the tire and body and the paint is still there.
The bottom bars should be parallel to the ground when the cars weight is on the ch***is. The upper bars should be adjustable in length and angle, and pointed somewhere towards the ground at a point determined by you. You need to figure out the weight and balance of the final car, and how you want the car to react in everyday situations. Having the uppers adjustable lets you fine tune after everything is screwed together.
Not necessarily. Put the instant centre too low and the car'll stand still spinning its wheels. Best to incorporate some adjustability so you can angle the lower bars up a bit if you need to.
If you really want an answer to your question you'd be wise to buy a suspension book and learn the theory for yourself. These guys are honest and sincere intrying to help you but the info and illustrations are confusing to the point of being contradictory.
I design and build Blower and engines/ drivetrain ***emblies for race cars and I just got to say Dawm.....thats stout! Under a car hauler my ***.....that needs to be in a tractor pullin' typa setp there!!!!! Great craftsmanship and execution, whatever in the hell it is! Don't think we gotta worry about it breakin'!
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