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Old 12-26-2005, 07:42 PM
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Triangulated four link rear suspension

Hello This is my 1st post on this bulletin board. I would like to know if anyone knows the geometry involved in figuring the relationship between upper, and lower bars, and their effect on pinion angle. I am making my own bars, and have decided on 36 inch lower bars, but don't know how long the upper bars should be. Should I just run the upper bars at a 45 degree angle(viewed from the top) and let that determine the length ? What angle should both bars be at (in relation to the frame) if viewed from the side ?? Any help would be greatly appreciated !! Thanks.

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Old 12-26-2005, 08:05 PM
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The closer the uppers and lowers to length, the better. the farther off, the more your pinion angle will change throughout its motion.
I believe you have to run the uppers at a 30 degree or greater.
http://www.illconformity.com/videos/linkvideo.wmv
this video might help you visualize link setups better
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Old 12-26-2005, 08:18 PM
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Or, you could run a single upper link and a Panhard, as with the 2005 Mustang.

If you're determined to go the triangulated 4link route, a search of the threads on this site will give you more information than you need.
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Old 12-26-2005, 08:27 PM
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Quote:
Originally Posted by david4991
The closer the uppers and lowers to length, the better. the farther off, the more your pinion angle will change throughout its motion.
I believe you have to run the uppers at a 30 degree or greater.
http://www.illconformity.com/videos/linkvideo.wmv
this video might help you visualize link setups better
Cool. Thanks for sharing that video.
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Old 12-28-2005, 02:23 AM
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triangulated four link

Wow!! That that video was great! So simple and yet so informative! This means that I am going to have to build a mock up of my own, and experiment with dimensions. Thanks Everyone!
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Old 12-28-2005, 09:23 AM
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No problem and good luck
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Old 12-30-2005, 08:57 PM
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Just remember that an over powered car can launch a paralell link 4 bar but an under powered one will need some downward angle on the upper arms or the tyres won't bite - compare super stock and pro stock suspensions. Trial and error, good luck and happy new year.
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Old 12-31-2005, 04:20 AM
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Don't know how it is in Australia, but, here, we try to make a distinction between 4bar and 4link setups. (Don't mean that as a "put down." I just realize that we might not use the same terms. If you're like Great Britain, for example, you drive on the roadway and the pedestrians walk on the pavement. Here, we drive on the pavement and the pedestrians walk on the sidewalk. I think it's "pavement." I've been listening to that Bucket woman on the BBCTV.) The 4bar is a parallel link arrangement where brackets at both ends force the bars to remain parallel at all times. The front bracket might be adjustable...up and down..., but the bars themselves are always parallel. With a 4link, the individual links can be adjusted, so that the link pair...on each side...is not necessarily parallel.

(Having said all that, I realize that there are still those here who use 4link and 4bar to describe either. Would be less confusing if we were consistent, though.)

The following applies to a RWD car with beam axle:

With a 4bar and the links parallel to the ground, the squat on launch is excessive. By angling a 4bar up until the bars are parallel to a line...as viewed from the side...which passes through the rear tire patch and the intersection of two other lines, one vertical through the front tire patch and the other horizontal through the car's center of gravity, the car will neither squat nor rise on launch.

With a 4link, if lines through the links intersect anywhere on the previously described line (which passes through the rear tire patch), the car will neither squat nor rise on launch.

(You might want to look at my "weight transfer" comments in the project files.)
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Old 12-31-2005, 10:06 PM
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No offense taken, road and footpath here (I drive on both). You aren't being pedantic, I wasn't sufficiently clear.
Yes a 32 Hiboy may run a 4 bar whilst a 69 Tempest and an EX BOB GLIDDEN Pinto run a 4 link of completely different design. What I am trying to get across is that the angle of the upper link is critical, if you run the lower link (not bar) paralell to the road with the upper link angled up at the front it mantains a fair pinion angle through compression but won't plant the tyre (not tire). Just like a stock GM a - body.
Angle the upper arms down at the front and it plants the tyre by pulling the floor to pieces. As I said, check out a few drag cars - the more powerful, the less angle on the uppers.

Last edited by IanRiordan; 12-31-2005 at 10:11 PM. Reason: last paragraph is superfluos
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Old 01-01-2006, 04:07 AM
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Road and footpath, eh? I have an amateur interest in etymology and I find this more interesting than most. Here, we would reserve "road" to refer to a 2 lane county road or a gravel road. "Footpath" has passed almost entirely from common usage. Before indoor plumbing, we might refer to the footpath to the outhouse. And, it retains kind of a romantic sense in that we might take a girlfriend on a walk along the footpath next to the river.

Anyway, what you might notice is that, if the intersection of the link lines of a 4link intersect on that no squat/no rise line that I described OR if the bars of a 4bar are parallel to that same line, pinion angle can be affected ONLY by the deflection of the control arms, since the suspension springs will not be affected at all during launch. With a 4link, the point of intersection on the no squat/no rise line is best as far forward of the rear wheels as possible so that track surface irregularities do not displace it. I think this is what you're seeing in these cars that you describe.

As for weight transfer (the "planting" of the rear tires), this is affected only by the center of gravity height, wheelbase, and acceleration. This doesn't mean, however, that suspension adjustments are totally ineffective. If the car rises on launch, CG height is increased. If the adjustment causes the rear tire loading to be more equal (left-to-right), the acceleration is increased. But, some adjustments provide only transitory benefit. By causing the car to rise, for instance, the initial effect is beneficial, but, as the car reaches its uppermost point, the rear tire loading is decreased. In other words, the rear tire loading becomes oscillatory. For this reason, I recommend neither squat nor rise.
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Old 01-01-2006, 11:51 PM
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Hey cuz, if you look at some of my previous posts you'll see I stress how poor our roads are. My mother is visiting for a month so I loaded her (wheelchair and all) into my 96 Holden Statesman and took her for a drive of about 130 miles. We went down the main roads to Victoria's main ski resorts - Mt Hotham and Falls creek,we toured the postcard towns of Harrietville, bright and Myrtleford then home to my hobby farm outside the picturesque old gold town of Yackandandah. Not once did we use a road with more than 1 lane each way, many secondary roads are still dirt and only 2 state capitals (the largest) are joined by a 2 each way dual carriageway.
Hell, when my parents married in 1953 the Hume hwy - main road between Melbourne and Sydney was 30% single lane dirt, nothing romantic about being AIRBORNE at the speed limit with a well set up sla front leaf rear car as happens whenever I cross Queensland headed for Darwin.
Oh yeah, a footpath keeps you out of the dung on a bridle path, or from being run down or robbed by a bushranger on a coach road. Many country towns still have a clearly marked and sometimes used stock route for drovers with their cattle.
Anyway we're holding up this forum so if you want to discuss 18/19th century dialogue still in use then contact me, if you wanna see 'squat' at work watch a pro - stock.
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Old 01-02-2006, 05:51 AM
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I'm not going to worry about holding up this thread. I suspect others are enjoying these comments as much as ourselves.

I married a Filipina lady about 3 years ago, which means, of course, that I've been to The Philippines, but only as far as Manila. Except for the vehicles found on its streets, Manila is not very different...streetwise...from cities here. The only signal lights, however, are located in the area around the airport. And, it didn't appear that our driver had the slightest notion as to their purpose. Didn't make any difference to him if they were red or green. My wife actually lived on another island and her descriptions of the long bus rides just to get to a computer so she could email me almost made the Bataan death march sound like a walk in the park. (I'm given to exaggeration, so please don't be offended.)

Sounds like Australia is much the same, which surprises me. When I was teaching at the General Motors Institute in the sixties, my first wife and I were actually considering moving to Australia. So, we had 3 or 4 Australian students...from GM Holden...to our home one evening for dinner. During the course of our conversation, my wife asked the inevitable question: What do you like most about the United States? The answer was the same from all and it surprised me. They liked the service stations! What??!! They went on to explain that, in Australia, the price of gasoline was controlled, so there was no incentive for gas station operators to provide anything "extra" to induce you to return. That got me involved in a more serious study of the type of government there and a realization of the differences between socialism and a representative republic. I quickly realized the lures of Australia were not worth it! (Of course, since then, the situation here has rapidly deteriorated and most people don't even know the difference between a republic and a democracy or that the country's founders openly stated their hatred of a democracy.)


We have a general uniformity in our road systems here which didn't exist when I was a child. Then, when you crossed a state line, you noticed that the license plates were not only a different color but, often, had a different shape and the road surfaces and signs were different. In Iowa, where I grew up, the narrow two lane highways that crossed the state had curbs. This meant the large trucks would cross from Nebraska to Illinois and the inside tire of their right side duallies would be spinning in the air all the way!
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Old 01-02-2006, 07:58 AM
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How would this type of setup work: Upper's (ahead of the axle in a "V" shape) connecting to the center on top of the pumpkin and going outward and fastening to the top of the frame. Lower's (behind the axle, parallell style) fastening to the underside of the axle and going straight back and fastening to the underside of the frame. Would this be practical, I didn't see it on the video.
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Old 01-02-2006, 09:49 AM
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Sure, Stat, that's pretty much the "classic" arrangement. The video seemed to be pretty much limited, in interest, to the pinion angle change encountered during large suspension travel. It wasn't really aimed at dragracers or street rodders, which, in my opinion, was unfortunate. Would have taken only a bit more time and they could have covered squat, rise, etc.
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Old 01-02-2006, 04:55 PM
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I've seen in a lot of magazines where they have the lowers ahead of the axle but I've never seen any behind the axle. That's the set-up I'd like to use because my frame is higher behind the axle so they won't hang to low.

Last edited by STATUTORY GRAPE; 01-02-2006 at 05:01 PM.
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