Which type of 4-link?

[ALLstrokedOUT]

Hello, Im starting the research for the next phase of my project. A soon as I get my truck on the road, my Demon is coming off for some changes. One change will be the crappy rear leaf springs.

Im wondering where you guys start when designing your suspensions from scratch. I want to keep the rear seat, and the fuel cell cannot move from where it is, but im not afraid to cut & weld anything else.
I was thinking of going with a triangulated 4-link, but is the triangulation enough to not require a watts link or other sort of centering device? With a triangulated 4-link, are you losing any noticeable articulation or adjustability?

This is the best picture I have saved of the space ill be working with from the fuel cell and existing floor (I plan on mounting the links inside the frame rails):
https://static1.pt-content.com/images/pt/2012/03/DSC01191-1.jpg (http://s179.photobucket.com/user/63vette77/media/Demon/DSC01191.jpg.html)

Thanks for the advice, I plan on making some measurements in the next few days, and sourcing out the parts- I plan making this from scratch, not from some sort of kit.

[Ron Sutton]

Hello, Im starting the research for the next phase of my project. A soon as I get my truck on the road, my Demon is coming off for some changes. One change will be the crappy rear leaf springs.

Im wondering where you guys start when designing your suspensions from scratch. I want to keep the rear seat, and the fuel cell cannot move from where it is, but im not afraid to cut & weld anything else.

I was thinking of going with a triangulated 4-link, but is the triangulation enough to not require a watts link or other sort of centering device?
Yes, assuming you're putting the links somewhere in the 40 to 60 degree range, the triangulation is enough to not require a track locating device.


With a triangulated 4-link, are you losing any noticeable articulation or adjustability?
Articulation limits vary from design to design, depending on the links, length, angle, mounting points, length difference (upper & lower) and to a degree, the types of ends used. The adjustability again, varies with design. I've seen set-ups with everything from no adjustment holes at any end, to holes at all 4 ends, like parallel 4-link.

Thanks for the advice, I plan on making some measurements in the next few days, and sourcing out the parts- I plan making this from scratch, not from some sort of kit.

Are you planning to compete in track events ... or just have a fun street machine?

[rjsjea]

Morrison Triangulated 4 link and Speedway engineering splined bar under a Demon. Looking at your pics, this setup would probably fit (we have similar fuel cells).

[ALLstrokedOUT]

Thanks guys, it used to be my full time daily driver, once my trucks done I'm hoping to make it driven every other day. But I'd be looking for a pretty good track setup, little to no consideration for street comfort ( I don't have any insulation or ac down here in 95+deg FL, hard suspension won't bother me).

[Bryce]

I would start to plan out the range of mounting point options.

Aim to have the LCA horizontal. Then chose an anti squat range you want to achieve. Keep the arms as long as possible. I think a tri4 is good for a drag car, but without the adjustable roll center it loses some necessary adjustability.

[Ron Sutton]

I would start to plan out the range of mounting point options.

Aim to have the LCA horizontal. Then chose an anti squat range you want to achieve. Keep the arms as long as possible. I think a tri4 is good for a drag car, but without the adjustable roll center it loses some necessary adjustability.


Agreed on all points. Except the triangled 4-link is not optimum for drag racing either.

[Bryce]

Agreed on all points. Except the triangled 4-link is not optimum for drag racing either.



Thanks Ron, agreed not optimal.

[Ron Sutton]

In drag racing, you want a parallel 4-link, so all of the pushing & pulling forces are ... well ... parallel with the car. You don't want any of the links pushing or pulling at an angle to the car.

Tim,
Bryce's suggestion to keep the lower links horizontal (level with the ground at ride height) keeps all of the roll steer out of the car. Then, just like Bryce said, you adjust the top link angles to achieve the intersect point (using imaginary lines) with the lower link's lines ... to achieve the anti-squat percentage you desire.

Keeping all 4 of the links as long as you can, as Bryce suggested, reduces pinion angle change as the suspension goes through it's motions.

Lastly, as a tuning tool, having the roll center be adjustable with a panhard bar or Watt's link as Bryce said, is a smart move for track days.

Best wishes.

.

[ALLstrokedOUT]

Thanks Bryce, Ron,

I was curious about the panhard bar/watts link...I have a couple 'beginners' suspensions books, im wary of the panhard as ive heard the lateral forces can sometimes bend them (although there would be a smaller force due to the upper links triangulation). I don't like the watts link because of the forces that have to be imposed on the differential cover.

What about the inclination of the upper links, can they be close to horizontal as well, how will this affect handling? Sorry for what seems to be an easy question, I should brush up on my books, its been several months.

[Ron Sutton]

Let’s talk Anti-Squat. If you run the upper links exactly level & perfectly parallel with the lower links … there is no intersect point … no instant center … and is considered zero Anti-squat. This will provide the most secure corner entry under braking … because the rear suspension of the car is not contributing to the pitch angle under braking. But it will provide the least grip to the rear tires on corner exit … because the rear suspension of the car is not contributing any leverage helping to load the rear tires.

If you adjust the upper link(s) … at either end … placing the upper link(s) angling downward in the front … there will be an intersect point with the lower links imaginary line … creating an instant center somewhere forward of the rear axle … and the rear suspension is considered to now have some percentage of Anti-Squat. The steeper the angle downward in front … the more Anti-squat the suspension has … and will mechanically contribute to the pitch angle of the car under braking … making the rear of the car lift more. But it will provide more grip to the rear tires on corner exit … because the rear suspension of the car will now contribute leverage helping to load the rear tires.

If you go too far … with the goal of gaining more grip for corner exit or hard drag style launches … and end up with too high of an Anti-squat percentage … you will make the car loose on corner entry under braking. The key is finding the right balance for your car & goals … and tuning it to achieve optimum set-ups for different types of driving if you become a serious competitor.

If you want to play around with different combinations, you should buy Performance Trends 4-link plus software. It works just as well with 3 links. See it HERE (http://performancetrends.com/4link.htm).

.

[Ron Sutton]

Thanks Bryce, Ron,

I was curious about the panhard bar/watts link...I have a couple 'beginners' suspensions books, im wary of the panhard as ive heard the lateral forces can sometimes bend them (although there would be a smaller force due to the upper links triangulation). I don't like the watts link because of the forces that have to be imposed on the differential cover.

What about the inclination of the upper links, can they be close to horizontal as well, how will this affect handling? Sorry for what seems to be an easy question, I should brush up on my books, its been several months.

I have never had a panhard bar failure ... other than when we bounced cars off of concrete walls.

I have worked a lot with both. If the panhard bar is adjustable on both ends, I favor it, because I can tune the roll center & fine tune the loading of the rear tires in LH & RH corners. If it's not adjustable ... well ... that's just silly.

I know a lot of guys prefer the Watt's link. I'd like to hear Bryce's opinion & others too.

[Bryce]

I know a lot of guys prefer the Watt's link. I'd like to hear Bryce's opinion & others too.



I am running a watts only to keep the rear perfectly centered. I can handle the roll without tire rub but if the rear end moved latterly the inside wheel well would hit the tires. Since I have a falcon the widest tire I could fit is a 275 and it just fits in the stock wheel wells. (one of my design requirements). I did not want a radiused wheel well.

I also designed a watts link that weighs only 8.4lbs so not much of a weight penalty compared to a panhard bar. The RC is a bit higher than what is attainable with a panhard bar, but I was trying to balance roll stiffness without a sway bar (packaging reasons it just wont fit)

[Ron Sutton]

There you go.

Thanks Bryce.

[Bryce]

There you go.

Thanks Bryce.

HAHA, anytime.

[ALLstrokedOUT]

thanks guys for the input Now, Heim joints or poly bushings? I suppose it depends on the degrees of freedom the piece is supposed to have. Any one have a good source for these ends?

[Ron Sutton]

I'm a racer, so we only run rod ends.

We need some guys with a lot of street experience with their 4-link to chime in on this thread & give your their experience & advice.

if we don't get any, you need to call some of the PT suspension vendors & ask about their customers' experiences. Then you can buy the ends from them.

.

[Bryce]

I only run rod ends as well. I don't really car about road noise or harshness. But it really isn't that bad. My Detroit locker is louder and harsher and I can barely hear it over the exhaust.

I recommend aurora, that's the only thing I will ever run again. When its time for an upgrade I will be switching the remaining heims with Aurora. I talk to Aurora every year at SEMA they make the best.

[parsonsj]

I ran rod ends and they were fine for a while, but after they broke in, I found them less tolerable. I like Spohn Del-spheres. They are nearly as accurate as a rod end, but reduce the NVH by using Delrin between steel.

I swapped my Z06 over to Delrin bushings from rubber in all 8 control arms this past spring. The NVH didn't increase to any noticeable extent.

I'll weigh in on 4 links too: Any linkage other than a parallel equal length setup (such as triangulated, shorter upper arms, or with the upper arms not parallel to the lower arms) is inherently in bind during body roll. Any roll depends not on articulation of the pivot joints in the arms, but on compliance of the components themselves. That seems to work ok for 3 or 4 degrees either way, but tuning near the edge of the compliance envelope can get tricky.

Non-binding rear suspension are 3 links and torque arms if the torque arm can move freely in all three planes.

Food for thought, anyway.

[marolf101x]

Rod ends or bushings?
Depends on what kind of person you are, and what you want out of the car. We offer rubber, poly, and rod ends, so I have been behind the wheel of all of them.

If you are the "I cannot handle anything louder than my new Lexus or my panties get in a bind" then you want rubber all the way. You'll have suspension deflection, but you don't really care as that doesn't matter when you drive the car to the show and park it where it looks like a damn fast PT car.

If you are the "I don't give a crap what it sounds like cause I only drive it to (or at) the track" then you want rod ends as you desire no "unwanted" movement of the suspension and you need every last bit of performance.

If you are the "I mainly street drive it, but I will take it to a few events" kind of person, then you may want one of each. Provides a little noise reduction while remaining pretty stiff.

I'm the "this is a fast Muscle Car so ride quality should be just before you piss blood, steering should be dangerously quick, and noise, what noise? My stereo goes to ELEVEN!" kind of person. (that being said I typically drive the 48 Hour Camaro and it is none of those things. . .it's relatively quiet, the Air Con sends a nice chill up my shorts when pointed in the right direction, the ride quality is a touch on the stiff side but I'd ask my wife to drive it 2 hours without a stop, it gets mid 20's MPG, and it's brutally fast for an old street car.) It does have Delrin bushings in all front control arms and rod ends at all links in the rear.

[Ron Sutton]

John & Britt ...

Thanks much for chiming in with your experiences. That is what he was looking for. :cheers:

.

[ALLstrokedOUT]

Yes, thanks to everyone so far!
No part of my car is made for comfort, and I only intend to make it more competitive on all fronts from here as time and funds permit. after the rear suspension I will be looking at the front suspension w/ C4 suspension (something ive already roughly laid out).
https://static1.pt-content.com/images/pt/2013/08/c4suspensionassembly-1.jpg (http://s179.photobucket.com/user/63vette77/media/AutoCad%20and%20Solidworks/c4suspensionassembly.jpg.html)

As I said before I have a lot to look into for this project, but I defiantly have a lot better of a direction now with a few names to look at for joints, and a bit to think about for the geometry.
In the coming weeks ill post up some drawings if you guys wouldn't mind giving me some criticism.

OH, one more thing to consider is ride height, and suspension travel: Currently w/ my Hotchkis leaf springs I have NO suspension travel and am resting on my pinion snubber with a full tank of fuel. Any spirited acceleration and those springs squat down like the engineers never heard of torque before. What spring rates should I be looking for, and what travel +/- from static ride height should I be looking to have?

Thanks again.

[marolf101x]

We design a minimum of 5 inches wheel travel into our systems. Typically 60% travel for compression, 40% for extension.

When you need to figure spring rates our calculator makes it easy and keeps the wheel rates where they need to be:
http://www.ridetech.com/tech/spring-rate-calculator/

[boodlefoof]

I'll give a plug for the Satchell link design. It packages well without having to cut into the floor or rear seat area and can be built to give a fairly low RCH and good anti-squat. I can't yet comment on street driving with rod ends, as I don't have the car on the road yet. Here is a picture of my in-process project.

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