[bigblockford79]

Got started on the design of my 4 link last night, and I am lost. My frame height is quite high but cannot be any lower or large metal parts start hitting each other. I do not want to have to build a gay azz cradle either, since right now the only things hanging down from the underside of my frame are driveshafts, a links, and link mounts. (the rig is basically a 79 f250 with a 6" suspension lift)

Please help. Here is the calculator that I ran to get where I am at currently.

Thanks In Advance

 

[SANDVIPR]

Well, I can't see how the numbers turned out very well, but the over-all design looks fine.
Are you planning on doing anything specific with it? That will determine a lot more on tweaking the design. If you are drag racing in sand a lot, you may want to make your upper link a little steeper to help get the power to the ground better. If you are going for rocks, a couple other changes may need to happen.

Please give us a little more background and I'm sure experienced others like 95GEO will chime in and get you pointed in the right direction. There a quite a few builders on here that know this stuff inside and out.

 

[bigblockford79]

Well, I can't see how the numbers turned out very well, but the over-all design looks fine.
Are you planning on doing anything specific with it? That will determine a lot more on tweaking the design. If you are drag racing in sand a lot, you may want to make your upper link a little steeper to help get the power to the ground better. If you are going for rocks, a couple other changes may need to happen.

Please give us a little more background and I'm sure experienced others like 95GEO will chime in and get you pointed in the right direction. There a quite a few builders on here that know this stuff inside and out.

I changed the picture to a larger one so you should be able to read the numbers.

I guess my biggest concern is that everywhere i read about how to set up a rear 4 link it says to keep the lower links between 5-10* and the upper should be as flat as possible. As you can see I have a size-able angle to both of my links. Is this not much of a concern as long as the numbers in the calculator come out ok.

What are good numbers to shoot for with the anti-squat, roll center, instant center, and roll axis angle?


The truck is going to be mostly a slower moving trail truck. It will see many different obstacles you would see at the various off road parks in the area. It will never see a drag race, and very rarely ever see mud.

 

[bigblockford79]

Bump......Please Help if you are able.

Thanks

 

[Monkeyevil]

Roll axis is too high.

 

[bigblockford79]

Roll axis is too high.

I can see that, how do I fix it? This is very new to me and I need some seasoned insight with suggestions on how to better design this so it works like it should.

 

[feva4u]

Start by changing link lengths/width locations in the spreadsheet and see how they effect the overall numbers. At the end of the day you have to package it and run it so packaging is really the initial problem.

 

[bigblockford79]

Start by changing link lengths/width locations in the spreadsheet and see how they effect the overall numbers. At the end of the day you have to package it and run it so packaging is really the initial problem.

Alright, I will have to bust out my measuring stick again and see what I can do to make changes without making a lot of sacrifice.

What is a good set of "target values" for the various geometry results.

Roll Center? I have read that around the area of the front bumper is a good point to try for. does this mean for the x and z values or just x?

Roll Axis angle? If you have to pick which would you rather see? Over or under steer on a strictly off-road vehicle? What effects will a higher number have on the driving "feel" and handling characteristics of the truck?

Anti-Squat? All of the references that I have checked have different schools of thought on this. Many say around 100% is good, others say 50-80%. Can anyone with a 4 link remember their # and give any input on overall handling with the set-up you're running?

I am really struggling with this since all information out there seems to be more based on street cars. Anything you find truck based, every other source contradicts the previous one.

**This is the last major stepping stone I have to get over to get this truck done. After this its basically putting all the little things back together**

 

[feva4u]

Here's mine if it helps
http://www.greatlakes4x4.com/showthread.php?t=115239&highlight=4+link

 

[bigblockford79]

Here is Version 2 - I think this is about as good as it will get based on the numbers that I tried changing. Of course any input from those wiser in this matter is GREATLY APPRECIATED.

Thanks

EDIT: If I lower my upper link frame mount just .5" i get 101% AS, IC X=135 Z=57. The rest of the stuff stays within the whole numbers shown in the pic.

 

[95geo]

What are you going to be doing with this truck? Why is it so tall?

I would make some sacrifices, it'll be worth it in the end. First, I would raise the lowers on the axle a little bit to help flatten them out, 1" above center is plenty for what kind of vehicle this is. If you can lower the frame side of the lowers even 1" it'll help a lot, closer to 2" will bring things a LOT closer to a managable location. It's either move the lower frame mounts down or lower the vehicle. If you're set on that ride height then moving the links down will give you almost the same result. If you plan on keeping it that tall, it will probably be worth putting some sway bars on to help keep it stable. If you can move the frame side uppers around a little bit it would help a lot to move them down and closer towards the lower frame mounts. Not a lot, but maybe just a couple inches in a straight line towards the lower pivot points.

It's all about the packaging!

 

[bigblockford79]

What are you going to be doing with this truck? Why is it so tall?

I would make some sacrifices, it'll be worth it in the end. First, I would raise the lowers on the axle a little bit to help flatten them out, 1" above center is plenty for what kind of vehicle this is. If you can lower the frame side of the lowers even 1" it'll help a lot, closer to 2" will bring things a LOT closer to a managable location. It's either move the lower frame mounts down or lower the vehicle. If you're set on that ride height then moving the links down will give you almost the same result. If you plan on keeping it that tall, it will probably be worth putting some sway bars on to help keep it stable. If you can move the frame side uppers around a little bit it would help a lot to move them down and closer towards the lower frame mounts. Not a lot, but maybe just a couple inches in a straight line towards the lower pivot points.

It's all about the packaging!

I want the truck to be an all-around rig, it is only as tall as it needs to be to package everything. I have dropped it 2" since making this thread. I only have 6" of compression with my coil-overs with about .750 of "cushion" before metal parts start hitting.

My lower axle mounts are already 1" above axle center line in the version 2 set-up.(only Pic posted now).

I played with some of the other stuff and got these new numbers. AS 93%, IC X=146 Z=57, and roll axis angle of 9* I dropped the frame end lowers 1" and the uppers another .5". Without murdering my ground clearance with a drop cross member this is about as much as I can move things and still keep it packagable.

AS 93%, IC X=146 Z=57, and roll axis angle of 9*

 

[bacongrease]

dont get overly worried about ground clearance, with a stable suspension youll be able to get on top of the highest parts of the trail without the pucker factor when being off camber or flexed out. make it stable and the build a flat skid even if it hangs down further than you would really like. done worry about antisquat, just build adjustment into your upper link frame side mounts, and at bare minimum have your lowers flat at full compression.

just my .02 cents

 

[Monkeyevil]

Try and triangulate the lowers at the frame and see what that does to your roll center.

 

[fabguy01]

So in a perfect world without having to worry about packaging, what would be the target numbers to shoot for

 

[bigblockford79]

Try and triangulate the lowers at the frame and see what that does to your roll center.

I did switch some numbers around and changed the design to true double-tri 4 link and my roll axis angle is now 3*, my IC is X 167 and z 57, AS is 87%. These will be the numbers that I build from. Its about as good as it will get without chopping the whole frame up and starting from scratch.

Not only that, no one seems to have any first hand info on what certain numbers for the variables will do for ride and handling. Just about every source I look at for info has different logic for what works best. As a friend said the other day "properly setting up a 4 link is OPINION, everyone has one and they are all different. But each person thinks theirs is right and the best one by far"

I found this site from Arizona. A guy took rigs that he knew performed well in REAL life situations, measured the link set-ups on these rigs and then ran the numbers through the calculator. There was a wide array of numbers, the vehicles were fairly similar tube chassis rock crawlers. Here is the article.

http://www.azrockcrawler.com/_images/tech/2007/6-27-074link/4linksurvey.html

This one explains some of the terms associated with link-type suspensions

http://www.azrockcrawler.com/_images/tech/2003/4-034link/4-034link.html

 

[95geo]

So in a perfect world without having to worry about packaging, what would be the target numbers to shoot for

no such thing.

I did switch some numbers around and changed the design to true double-tri 4 link and my roll axis angle is now 3*, my IC is X 167 and z 57, AS is 87%. These will be the numbers that I build from. Its about as good as it will get without chopping the whole frame up and starting from scratch.

Those numbers "sound" pretty neutral.... Run it and see how it works.

Not only that, no one seems to have any first hand info on what certain numbers for the variables will do for ride and handling. Just about every source I look at for info has different logic for what works best. As a friend said the other day "properly setting up a 4 link is OPINION, everyone has one and they are all different. But each person thinks theirs is right and the best one by far"

Different zones of variables will give you different handling traits but there isnt a fine line for the changes... that's why it's so hard to pinpoint exactly how something will handle unless you have a baseline to make changes from.

I found this site from Arizona. A guy took rigs that he knew performed well in REAL life situations, measured the link set-ups on these rigs and then ran the numbers through the calculator. There was a wide array of numbers, the vehicles were fairly similar tube chassis rock crawlers. Here is the article.

Chris V. and all of those guys have their rigs dialed in very well. But, a lot of what they run wouldnt be the greatest to base a multi purpose rig on. They build those vehicles to shoot waterfalls that are 30-100' tall. Their rigs work well in a wide variety of terrain those setups vary a lot from a southern rig or a west coast rig.

 

[SHARPMACHINE]

So in a perfect world without having to worry about packaging, what would be the target numbers to shoot for

Some notes I have saved below. Alot of it from guys on here. As said there is no magic. It is real hard to wrap your head around the first one, if you think about it to long.

SUSPENSION SET-UP GOALS:
1. ~ 21-23” BELLY HEIGHT (BRIMMY311 @ GL 4X4) MY SILVER JEEP = 24” TO BOTT. OF TUB & 19.5” TO FRAME.
2. SUSPENSION TRAVEL = 11-12 INCHES??? USE 5-6” OF UP-TRAVEL WITH BUMPSTOPS.
3. LIMITING STRAPS, CAN SEATBELTS BE USED OR TOW STRAP MATERIAL OR??
4. WIDTH = OUTSIDE OF TIRES = 74 (JEEPFREAK81 ON FULLWIDTHS & H1’S)? SODAPOP SAY 75 WOULD WORK WELL? YETTI SAYS MICHIGAN TRAILS ARE RATED FOR 72”, BONES SAYS THAT IS TO NARROW?? LIV2MX SAYS HIS TJ IS 78” FRONT & 76” REAR.
5. LENGTH = TRAILS, GO WITH ~ 100.” & BEST OVERALL ~ 104-106”
6. 95GEO suspension notes =
8" of axle seperation * 4-6" of frame seperation in the rear * 3-5" in the front, a total horizontal seperation of at least 30" combined from parallel links make the lowers as flat as you can get them at ride height, full stuff they should be down hill for the best performance. link lengths between 32 and 40" C-C is the best balance for performance and packaging. it's pretty straight forward, buy the brackets from poly performance and ask questions when you are unsure of something. read lots and look at as many examples as you can.
7. on 35's your looking for about 1/8" toe in and 4-6 degrees caster...camber is unadjustable except with custom ball joints. The factory alignment settings do not work with aftermarket lifts. (POSITIVE CASTER = TOP BALL JOINT LEANS TOWARDS REAR OF VEHICLE

 

[bigblockford79]

Those numbers "sound" pretty neutral.... Run it and see how it works.

Different zones of variables will give you different handling traits but there isnt a fine line for the changes... that's why it's so hard to pinpoint exactly how something will handle unless you have a baseline to make changes from.

.

This is pretty much what I have to do, every rig is a little different and I won't know what works best for mine until I have a starting point to improve from.

 

[fabguy01]

no such thing.

? so you are saying that ther is no target #'s for anti squat, roll center, effective center ect, ect. that seems odd