3 link vs triangulated 4 link - Why is one better?

[Just 1 More]

I know this has been discussed before, many times BUT, talking performance only, not cost, not installation, just performance, triangulated not lateral 4 link.
... I keep hearing the 3 link is so much better than a triangulated 4 link for auto-x performance and I don't understand why. If you take both set-ups and add the ridetech "R" joints on all ends, you would not have any binding, IMO, So,

4 link with all ridetech "R" joints
3 link with all ridetech "R joints

The 4 link would not have any binding, correct?
The 4 link would control any side to side movement, correct?

The 3 link would allow the rear to move side to side slightly with articulation due to the track bar, correct?

So what makes one better than the other?

I did put the complete Ridetech R joint kit in my Camaro and the articulation was just as Brett showed it in his R joint videos. My FFR 33 has the option of doing either and already has the 3 link bracketry if I want to go that route. I already have all the 4 link set up with all R joints. Remember that money is not the consideration here, strictly performance. What would I gain going to a 3 link?

[CSG]

You will need to plot out all the geometry on that platform to really tell the differences between the two. Typically you do still have some bind with the 4 link but personally I find it negligible in most well designed applications with short travel numbers. I would be comparing the numbers...

[Just 1 More]

You will need to plot out all the geometry on that platform to really tell the differences between the two. Typically you do still have some bind with the 4 link but personally I find it negligible in most well designed applications with short travel numbers. I would be comparing the numbers...

Where would the bind come from?

[CSG]

Where would the bind come from?

From the axle geometry changes during suspension travel, think rear steer. If you search around I have seen Norm Peterson make some informative posts and have seen a few examples. On a setup like the ridetech they did not use a panhard bar, I assume for cost. This caused the design to have to angle the links a lot for axle lateral location. Think about how the axle would move around with one side fully bumped & the other fully extended. The force to "move" the axle is typically considered bind. With more parallel links and a panhard bar there is not as much movement (DSE). I have never driven a ridetech car but I would be surprised if there is zero snap oversteer. I am certainly not a suspension engineer so if anyone wants to shoot holes in this then have at it...

[dontlifttoshift]

Any time you ask a part to do more than one job, you end up with compromise. So for this particular discussion, I will take the 3 link with a separate lateral location device over a triangulated four link every time.

A separate lateral location device also allows for a lower roll center than you can get with most triangulated four links.

[dhutton]

What did ridetech do on their FFR 33? I would think that is a useful datapoint.

[Just 1 More]

What did ridetech do on their FFR 33? I would think that is a useful datapoint.

Funny you mention that, I've actually been in contact with Brett a few times and he's been a great source of info although kind of limited since they recreated everything in the front steering, he said.... "Their suspension geometry is not terrible and even the steering geometry wasn’t bad, just too light of components."
Which is why I had ridetech build me the lowers and went with their uppers.

[stab6902]

Any time you ask a part to do more than one job, you end up with compromise. So for this particular discussion, I will take the 3 link with a separate lateral location device over a triangulated four link every time.

A separate lateral location device also allows for a lower roll center than you can get with most triangulated four links.

Hard to argue with Donny's perspective from a pure performance point of view. 3 links will also generally be more tunable.

3 link setups usually don't package as well (the top link goes right where a lot cars have their back seat) and don't play as nicely with traditional ladder frames, but that's not a concern for you.


I doubt many drivers could tell the difference between the two from behind the wheel assuming they were both well implemented and tuned.

[Just 1 More]

Any time you ask a part to do more than one job, you end up with compromise. So for this particular discussion, I will take the 3 link with a separate lateral location device over a triangulated four link every time.

A separate lateral location device also allows for a lower roll center than you can get with most triangulated four links.

In this particular application, roll center should be the same since the lower link bars and shock mounts are in the same mounting location for either. The only difference is one has 2 triangulated upper bars and the other has a single upper bar and a panhard bar.

[dontlifttoshift]

Rob explains it pretty well at the bottom of the first page. https://www.pro-touring.com/threads/...enter-question

[jetmech442]

Hard to argue with Donny's perspective from a pure performance point of view. 3 links will also generally be more tunable.

3 link setups usually don't package as well (the top link goes right where a lot cars have their back seat) and don't play as nicely with traditional ladder frames, but that's not a concern for you.


I doubt many drivers could tell the difference between the two from behind the wheel assuming they were both well implemented and tuned.

Rob explains it pretty well at the bottom of the first page. https://www.pro-touring.com/threads/...enter-question

Just1more,
I spent the past couple days organizing my thoughts to try and share my experience with my 4link/watts combo and then my 3 link conversion. I'll post it in a new link as it is a longer post, but hopefully organized and helpful.



The link Don'tlifttoshift posted is a great read from some very helpful members, and I would like to add/contribute. I've read a ton of posts from him and generally agree with his views with the exception of not lifting to shift(his poor synchros lol).


I also agree with Stab that it would be hard for most drivers to tell the difference, especially on the street and occasional autocross. I think the two start to diverge on HPDE and track days.

[jetmech442]

The following are some thoughts I’ve had with my experience with A bodies, in particular my ’69 olds, though I assume a lot of this applies to early Fbodies as well. My expertise is in thermal systems, not suspension, though I have put quite an effort to learn suspensions. In trying to write this I expose my ignorance on the subject and ask if something doesn’t sound right, that you add to the knowledge and educate us all.

I care about 4 things for the rear suspension.
1) Instant center(Antisquat),
2) roll center height(under-over steer),
3)roll center migration(predictability/stability),
4)rear steer effects from suspension movement(loose/tight in corners).




1)Instant center
When the car is lowered in typical protouring fashion(just a few inches, nothing crazy), the antisquat is raised considerably by angling the arms severely down towards the driveshaft. High Anti-squat is good for the street because it helps the tires hook on a hard launch, but on track it unloads the rear tires in hard braking, leading to either very dangerous wheel hop or forcing you too dial the proportioning valve so high that the rears do nearly nothing anymore and total braking capability is reduced by 15-20%. On a 4 link, there is no ability to reduce the antisquat without frame-side modifications.

If the 4 is converted to a 3 link, there is opportunity to easily build in AntiSquat adjustment. I built mine for approximately 30, 60, 90, 120, 150 180% antisquat adjustability. First cause I wanted to drag race,and autocross and track day and have the ability to set it up perfect. But...mostly cuase I didn't know what was good or bad and wanted teh whole range. As I've fallen in love with HPDE events, I keep my AS in the 30 setting.

On transient launch, the tires receive additional force due to accelerating the rear body away from the ground. But on braking they unload the rear tires as they pull the body downward. This causes aggressive rear wheel hop as the tires unload, lock up, then load again then repeat until pants are brown. My experience here was running 100% AS, and having wheel hop. I then moved it to ~30% AS and wheel hop went away. A higher AS might work, but I haven’t had the chance to explore.


2. Roll Center:
Once the front end geometry is fixed either with new spindles or tall upper/lower ball joints, the front roll center is set usually just above ground level(up from below ground level with original geometry). Assuming the camber/castor spring rates/sway bars are as good as they are going to get, then the front end grip is maximized. The rear roll center is the only opportunity to change the cars dynamics.
When the car is lowered in protouring fashion(just a few inches, nothing crazy), the rear roll center is raised high into the trunk area. It is a virtual Roll center obviously, but the effect is to make the car oversteer. With my setup, it makes very little grip in the rear ever, which is fun for a few days cause it’s easy to drift and act like an idiot on the street, but way too sensitive on track or autocross.
Because of the steep angles on the upper arms, any suspension movement makes the roll center wander vertically. This makes the rear end even less stable as the rollcenter, antisquat and pinion angle change a lot on corner entry. The effect of roll center migration is the grip level changes as the car settles into and out of a corner.

For a 4 link car running a watts or panhard, you have two rollcenters, one physical and one virtual. The physical one wins until your system binds, once the system binds, it will tense up and un-bind quickly, which is very not cool in a corner. While testing the limits of the setup I encountered this and went straight home to change it back. To be fair, the watts was in the lowest position which I have never since had the need to go to for any driving. When I moved to my 3 link, I wouldn’t encounter that binding issue…but I still have no need to run the rear RC that low. So I can see a setup running a 4 link and an adjustable watts, and as long as the watts in run in a normal range and you have either rubber or non-binding links(no poly here), then you could benefit immensely from a stable, adjustable Roll Center.
What I love about the watts link, is I can change the location of the Roll Center with a single bolt and change the rear grip level. At Autobahn country club I like it two notches up for a bit looser rearend to help some of the slowspeed corners. At Blackhawk I put it back 2 notches lower for more rear grip. Again, I don’t need a 3link for this, my 4 link with the watts would have been great, but my 4 link would have been stuck with very high antisquat which is awful for braking zones.

3. Roll center migration
Linear cars are stable and predictable. Anything variable adds extra stuff for your brain/hand combo to figure out on track. Variable rate springs, variable rate steering boxes, brake pad coefficients that increase significantly as they get hot going into a corner and roll center migration are the ones I know of.
Front Roll Center on A bodies is pretty much set once the standard upgrades are done. In the rear, the stock 4 link Roll Center moves vertically several inches as the car leans into a corner. This changes the grip as you try to get the car to take a set, then when it comes out of a set it does the same thing on corner exit. A Frame mounted Watts link locks the roll center where the propeller bolt is. An Axle mounted watts link is still at that bolt location, but will move up and down with the suspension. Not as much RC travel as a stock 4 link, but it still moves however much you let your suspension move. For reference, the change in RC height for Blackhawk vs ABCC is only 1 inch and that makes the car perfect for each track.

4. Rear steer effects.
I offset my lower control arm link so that both would be parallel when 280#bigboi was in the driver seat. My thoughts when doing this would be a car with predictable rear steer when it was just me driving. The frame side mounts have adjustment holes so I can angle the arms up, level or down. Angled up should make the axle turn into a corner, angled down should turn out. In reality I have not messed with this at all. They sit at level setting. Doing it again I’m not sure I would offset the mounts, or worry about this at all. I haven’t had any experience changing settings, it could be awesome or awful.

TL;DR
In my opinion for a fun street/protouring car, I would add a frame mounted watts link to every stock 4 link. The 4 link would need non-binding bushings to allow as much travel as possible before the two Roll Centers start fighting. You’ll also have high antisquat which will help launching hard. If your car is slammed, I don’t think it’s a good idea as the virtual roll Center will be super high and would probly just bind instantly even with reasonable watts settings. This setup also prevents the axle from laterally shifting and rubbing/cutting tires on corners.

For a more focused track setup where heavy braking is expected, I don’t think the 4 link/watts combo works at all due to the high antisquat. This is truly where a 3 link can do wonders. It will, by necessity have a lateral location device like panhard or watts, should be able to adjust Antisquat, and should provide the most stable setup.

Hope this helps and if anything feels contrary to your equations or experience I can discuss and correct.

[dcozzi]

Would a 3-link offer better articulation without bind?

Also, if you are going with a 3-link, isn't it kind of a no brainer to use a Watts link?

[chevelletiger]

Panhard bar.
I've made a wattslink for mine but changed direction and I'm doing a torque arm.
I know tony g from abc performance still uses the stock for link in his 70 chevelle but changed the upper pick up points on the top rear crossmember.
You might check with him and pick his brain,I just decided to jump head first with the TA and ls swap.F it!

[chevelletiger]

Could you share your pictures of those LCA mount with the modifications you did?

[jetmech442]

Would a 3-link offer better articulation without bind?

Also, if you are going with a 3-link, isn't it kind of a no brainer to use a Watts link?

Yes, a 3 link offers more articulation over a 4 link without bind.One of the points I try to make above though, is how much travel we need in a protouring car before it binds? It depends on the rear roll center height you need, and weather you want a lowish movement/low lean setup, or one that moves around and leans in corners.

In my opinion, if you go to the effort of fabbing a 3 link, a watts is not much extra effort and offers that locked in RC. But, in the case of A-Bodies, it requires a new nova gas tank(or a fuel cell in my case) and that is understandably a deal breaker for peeps that have already spent big money on an EFI tank.

Panhard bar.
I've made a wattslink for mine but changed direction and I'm doing a torque arm.
I know tony g from abc performance still uses the stock for link in his 70 chevelle but changed the upper pick up points on the top rear crossmember.
You might check with him and pick his brain,I just decided to jump head first with the TA and ls swap.F it!

Yeah, you can correct the aggressive antisquat if you modify the top rear crossmember mounts, but that is a lot of work as well.

Could you share your pictures of those LCA mount with the modifications you did?

Gladly.
Again tho, Mark Savitske told me this was probly not the best idea to offset them, and business troubles aside, I trust his opinions(trust them, I just didn't listen to them cause I love learning the hard way apparently). I loaded down the driver seat with bags of salt, which admittedly is now how I see myself these days ...how many bags of salt I carry around, sigh.

[chevelletiger]

Jetmech442,when you say offset are you referring to the lca mounts out to the sides like stock?

If so that's why the SpeedTech lowers didn't work for me ,they bound like crazy on my car.

I'm just going to keep the arms I machined with the del sherical frame end and rubber bushings on the axle side.

I would say doing the TA or 3 link is more work then modifying the upper crossmember, IMHO.
I posted the SpeedTech TA in the for sale ads but I think I'm going to just keep plugging away at it.
But get rid of the lower control arms.

[jetmech442]

Jetmech442,when you say offset are you referring to the lca mounts out to the sides like stock?

If so that's why the SpeedTech lowers didn't work for me ,they bound like crazy on my car.

I'm just going to keep the arms I machined with the del sherical frame end and rubber bushings on the axle side.

I would say doing the TA or 3 link is more work then modifying the upper crossmember, IMHO.
I posted the SpeedTech TA in the for sale ads but I think I'm going to just keep plugging away at it.
But get rid of the lower control arms.

Hey, when I say offset I was referring to the vertical position. I added 280 lbs of salt into the driver seat, and welded the lcas in a position that both lower arms would be perfectly parallel. The idea was to eliminate rear steer variability from left it right turns.

I heavily considered a Torque Arm, and still a close second to the 3 link. one of the things that stopped me was a desire to have a tuneable anti squat. I had no idea what a good setting would be with all the drastic suspension changes, and I didn't want to be stuck with a setting that didn't work. When I looked at the big names selling ta's there was no mention of AS or driving characteristics so I went the other direction.

[chevelletiger]

I see,thank you for the explanation
I'll post some pictures later today,I have my car lowered pretty good in the back, and my lca front angle up about 2°-3°
I agree on the after market no really having tuning into there packages, probably because most guys want to bolt on and run it.
Which is understandable

[74PanteraGTS]

I'm finally getting to my Chevelle. I spoke to Marc at SC&C a long time ago and he said basically the same thing that JetMech did about adding a frame mounted watts for a fun street car. Talked to Jim at Fays 2 a month ago and he agreed and should have the next run of A Body Watts ready soon. I have my Frame FX kit almost fully installed now and am adding ChevelleTiger's braces. Got to thinking that a torque arm setup couldn't be that much more work, but after reading this thread, I think I'll just listen to what everyone is saying, add the Fays2 Watts, new upper rubber bushings in the housing and be done with it. As I'm learning, time management is becoming more of an issue. I just inherited a mint 74 Nova that I may make a few mods to and I'm still chasing electrical gremlins in the Pantera. No need to make more work for myself when my plate is already full! Great info guys!