I was looking at photos of different hot rod rear suspensions this morning. I came across a photo of someone's parallel four bar rear suspension where the bars were angled inwards from the rear end to the outside of the frame. The bars at the frame used straight urethane threaded rod ends mounted on an angled mount welded to the frame. But the urethane ends welded to the bars on the rear end were welded in an angle. Something between 7 to 11 degrees from the angle the photo was taken. The mounts on the rear end were not angled. Depending on the HP of the engine is having an angle bushing, either welded or an angled threaded urethane rod end, safe on the rear? I don't think I had seen this done before on a rear suspension. I have seen it many times on 4 bar front suspension. Any thoughts?
For starters, what you are describing is not a parallel 4 bar setup. It is a triangulated 4 bar. And yes, usually the bar ends are at 90* to the bars with the mounts angled to suit.
Having the mounting points perpendicular to the ch***is centerline with a triangulated 4 bar is, I expect, an attempt to reduce bind / twist in the bars, which I suppose is achieved with the ch***is and axle remaining parallel. But with one wheel bumps or roll on turns, that isn't happening, and could arguably induce more twist, or twist more of the time? Heck, there might even be some subtle cleverness going on, like anti roll? Chris
It was not a triangular 4 bar. I guess I did not give a good enough description. I wish I had copied the photo, but I didn't. I was deep down the rabbit hole when I saw the photo, not sure how to find it again. But I made a crude drawing to demonstrate what I meant, hopefully. The top image is from above. It shows the angle of the bars inward. The bottom image shows from the side, thus parallel 4 bar. The middle image shows how each bar appeared. The frame end used a threaded urethane rod end. The rear housing end had the urethane outer tube welded in an angle on the bar. The mounts on the housing were straight, for the shocks to mount on. The bar, when bolted, was angled inward due to the welded urethane bushing housing. So, under hard acceleration, the lower bar is under compression while the top bar is under tension. How would those forces react to the angled bars mounted to the housing? If the bar is strong enough, would the mounts be bent? With triangulated 4 four, the bars and mount are inline so there is no side force applied, theoretically I ***ume. Any engineers out that with their slide rule?
I don't think there is anything "wrong" with that design as far as keeping the rear axle in position for regular driving, the ugly comes in if you are interested in serious high-performance drag racing use. You don't want to put high compression loads on a bar that already has a bend in it (at the welded-on rear end pivot, as you illustrated), it's always better for those forces to act in a straight line. Also the bars are pretty long for a serious drag racing application. For a street rod, it should work fine in combination with a Panhard bar or Watts link. Consider that four bar suspensions are sort of frowned upon here on the HAMB for the most part, although there were many cars built pre-'65 that had four bar suspension at one end or the other.
My 4-link is set up this way, no slide rule required. It is all CAD now. The bars are closer together at the leading end. The point to an imaginary point on the roll centerline. Doing this cuts down on the rear axle steering the rear of the vehicle on suspension cycling, like it would with a 4-link that is parallel when viewed from above. If you will, as the suspension links move up when one wheel goes over a bump, the axle moves forward. With the leading ends closer together, the axle moves forward a lot less. With the correct length of link, and the right spacing at the leading end, rear-steering can be virtually eliminated during normal suspension cycling. Of course, this vehicle also has a Watt's Link, IFS, stiff springs, and large anti-roll bars.
My thinking is that what AltBantam has drawn would still require a panhard bar. It is just a parallel 4 bar with the front mounting points angled in. A triangulated 4 bar has the upper bars mounted toward the center of the differential and angled outward in a line toward the mounting points of the lower bars, but generally shorter. Each pair of bars then forms the triangles that controls the rear's lateral location. They also control the amount of pinion angle change during the up/down movement of the rear.
Parallel 4 links is more of a performance suspension. Performance being going fast for 1320. There are few speed bumps on a drag strip. There is more to it than being parallel the links are also adjustable to set up instant center and commonly a noisy suspension because Heim joints are used in place of rubber bushings. Canyon carvers/auto crossers would probably benefit from a triangulated suspension, over a parallel suspension.
I used a 70 Cadillac rear end in my 49 Buick. I also used the 4 bar setup that came with the rear end. The top bars are mounted toward the center of the rear end, then angled out to the frame, the bottom bars are straight ahead to the frame. The angle of the top bars keep the rear end centered in the frame, so a panhard bar is not needed.
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