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Old 04-14-2011, 10:04 PM
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Traingulated 4 link confusion

Hi all.
My car is a 1963 Sunbeam Alpine with a Ford V6, tremec T5, with a narrowed Ford 8 inch rear with a currie aluminum carrier with a 4.11 eaton true trac in it. I've autocrossed it a couple of times, and I'd like to do more autocrossing and maybe get to some track days, but my leaf springs are shot. I've looked at a lot of different link type setups on this site and want to have something similar on my car. I lifted my car 2 or 3 times and took plenty of measurements and then started playing with one of the online suspension calculators. I think I have a setup that will work under my car, and was hoping some of you more knowledgable folks on here will tell me if my numbers look good and if I'm going in the right direction. The car is 95% a street car with a little autocross and such. Thanks for any suggestions, ideas, criticism, etc.
Im confused to what are ideal numbers for roll under/oversteer, and travel roll axis. Attached is my preliminary measurements. Thanks again.
Robbie
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Old 04-15-2011, 06:54 AM
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for a autocross car i would go with a parallel link arrangement with a watts link.
lots more room for error and will work better in this application than a triangulated set up.

there is some compromises made with a triangulated 4 link one of them being bind and it also has a tendency to react under power.

like this...
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Last edited by mud bros; 04-15-2011 at 07:03 AM.
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Old 04-15-2011, 08:47 AM
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I tried to do a parallel in the calculator and couldn't get under 5* roll oversteer. I've always been told for handling involving turning in 2 directions you want 0 roll oversteer or a little roll understeer. I wanted to go with a satchell but it would require too much rearranging of everything under the back of the car.
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Old 04-15-2011, 09:12 AM
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I Also thought parallel 4 links had more chances to bind, that's why rock crawlers usually go with triangulated?
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Old 04-16-2011, 01:08 PM
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To me, your problem is going to be welding your upper links onto your aluminum carrier case, which you most probably have to do. Your use of the calculator looks correct to me but with out the dimension it is hard to say how accurate you are. I think you would be very happy with the Tri 4 bar for autocross, if it is properly designed and installed. Using fully adjustable coil overs would be a plus for different course setups.

Trees
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Old 04-16-2011, 02:32 PM
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Quote:
Originally Posted by socorob
I Also thought parallel 4 links had more chances to bind, that's why rock crawlers usually go with triangulated?
the big difference is the watts link vs panhard as the panhard travels in a arc and the parallel links only like to go up and down.

the watts link allows the axle to travel vertically to match the natural movement of the control arms

also take into account you will only have 3in suspension travel and alot of times you have to make some comprises that have to be addressed from other avenues like spring rates,preload, sway bars,engine placement.

your correct in the thinking that triangulated is better for flex and articulation without bind something we want to stay away from on a autocross car
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Old 04-16-2011, 02:33 PM
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The housing is steel, only the removable carrier is aluminum, so I would be welding to steel. I plan on using adjustable coilovers, but I'm having a hard time deciding on what spring rate to go with. Do you think I'll have any side to side movement of my axle with this setup?
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Old 04-17-2011, 11:07 AM
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For only 3 inches of spring travel I think I'd simplify things and go with a Panhard bar. Make adjustable brackets and you will be able to change the height easily. Mine is only 19 inches long C to C. Do the math and you will see that the side to side movement of the body is pretty small relative to the complexity of a watts.

I also use a true 4 link on the street. It is more of a drag race set up than autocross. Granted it is not optimum but I don't spin the tires much...it just digs in and goes. Handling for a small tire, big tire short, wheelbase car is not bad.

If you are going for autocross and some kind of 4 link I surely would get a good book on the circle track car suspensions. Many use a true 4 link that is way different than a street/drag set up. They have many more adjusting points and you can set up a rear steer that will be unbelivable since you won't really have the restriction on this that the circle burners have. You already have the program to assist you in the set up. I surely don't have the technology to set one up but I have seen them and asked questions of the owners. You just need the technology to input into your program.

As for coil over. Surely get double adjustable shocks. Be prepared to have them re-valved for your car. I had to do this on my streetrod.

Springs will be a tuning device so you will need several to get just the right combo.

Might as well be prepared to buy or make anti roll bars front and rear. make sure they are adjustable and the bars are easily replaceable.

I tried a diagonal track bar vs the Panhard bar. I set the car up so I could test them simply by removing one and replacing it with the other. I nearly went off the road the first time I jumped on the gas with the Diagonal bar. It now resides in the scrap tubing pile. With the Panhard bar the car launches straight and true and tracks nicely around corners....not a sports car by any means but very drivable. Just my experience testing.

Last edited by bentwings; 04-17-2011 at 11:14 AM.
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Old 04-17-2011, 10:34 PM
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Did you model a 3 link with a panhard? That, in my opinion, is the best link suspension for a live axle rear end if you want to be able to put the power down and have plenty of articulation.

Typically with a panhard, you can get a lower roll center than with a Watts link, and if you make it as long as possible, the lateral movement with travel won't be as issue.

Andy
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Old 04-18-2011, 06:19 AM
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I don't have anything that's very structural in the middle of the car. Is a 3 link better with the center link above the diff or offset to the passenger side some?
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Old 04-18-2011, 06:37 AM
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I have always put the upper link offset to the passenger side to keep the overall bracketry height as low as possible.
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Old 04-18-2011, 06:45 PM
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If I have any side movement in my tri 4 set up, I can not tell it. By fully adjustable coil overs, I mean you can raise/lower the ride height and you can tune the shock rebound rate. I don't autocross, but do live in the mountains where cornering is important to me. There is no comparison between my tri 4 with fully adjustable coil overs and my parallel leaf set up with sway bars. Not exactly apples and apples, but not apples and oranges either.

Trees
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Old 04-18-2011, 09:54 PM
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Im partial towards the tri 4 link because i dont have very much room under the rear as its a small car. Here is a video to see how small...

http://www.youtube.com/user/socorob
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Old 04-18-2011, 10:36 PM
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I certainly understand limited space. My latest project car to hit the streets (and track) is a 97 Jeep Wrangler with Corvette C4 suspension front and rear. Talk about a tight fit!

The four link set-up is great, just be sure to use link bushings that will articulate. Heim joints are not so good on the street. Dirt and water will kill them quickly. I have thought about using Johnny Joints (see attached) on some future project. Good movement, are sealed, and rebuildable.

http://www.summitracing.com/parts/CUR-CE9112P/

They are spendy, but if you at least use them on one end of each of the four links you will have good movement in roll.

Roll understeer is preferrable to oversteer. Neutral, as your diagram indicates your layout seems to be, is okay. You anti-squat might be a bit on the high side. If you go too much, you can experience wheel hop under hard braking. You could make the frame brackets for both the upper and lower mounts with several mounting holes for tuning.

Good looking car! What do you currently have for anti-roll bars? It looks to have a fair amount of roll.

Andy
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Old 04-19-2011, 07:08 AM
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I have a 7/8 roll bar up front, the biggest available for my car. None in the back with worn leafs and shocks. That's what is getting me ready to do this, the need to replace everything back there. May as well upgrade while I'm doing the work. What's a good antisquat for a street/ autocross car? If I put my lower bars straight, the antisquat goes to about 90 but I get about 5 degrees of roll oversteer, seems the be the same if I try a parallel 4 link.
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