4 link anti-squat question...

[crashandburn]

I've got this 94 S10 Blazer with a 3 link SAS up front and triangulated 4 link in the rear. It works fantastic, except one thing. The torque roll is pretty bad. It can be pretty scary climbing a rock on the driver side, while the passenger side is my strong side. I recently read that antisquat can cause this. Previously I hadn't given it much thought because it does not squat or lift under load. It stays put really nice. So I thought my antisquat was good. I have no sway bars and a lot of suspension travel.
My question is: Antisquat is calculated as the relationship of the angles of the upper and lower control arms, as they relate to the center of gravity. I can map out the control arms and where they would theoretically meet, but how do you figure out where the COG line is?
Being a full bodied rig, I could only get my upper control arm mounts on the frame as high as I could get them. I do have pretty good separation at the axle. Based on the problem I'm having, should I try lowering the attachment point of the upper control arms at the axle?

 

[Blue85]

Have you read this? https://www.crawlpedia.com/4_link_suspension.htm. Instead of COG, they use the wheelbase and height of the engine crankshaft. Have you run the 4-link calculator spreadsheet?

 

[Tnsejed]

COG can be measured with scales, but a good guess will be fine as well. Going for the top bolt of the bellhousing can work as long as you are not loaded down with stuff up top.

The position of the third link and which side it's on, your roll axis slopes, your AS , etc all affect this (FRONT AND REAR). Torque lean can be a thing, and depending on the type of climb you're talking about it can make or break the line. Huge climbs and really offcamber scenarios change the numbers dramatically. That's why when your on a 8' waterfall things get strange and you're numbers are way different than the static model we use to build. Post up the numbers in the 4 link calculator.

It's also good to say that this can be more or less normal, but you want to build to keep it reasonable as geometry can exagerate it.

Also, real world is when you plug all your numbers into the calculator and you may find that it would take a full rework to get everything super happy. Don't fret, theres a shitload of trucks out there like that and they can still do some amazing lines. Sway bars, springs, etc can all help.

 

[crashandburn]

Talking with a few people, I'm moving away from thinking it is an AS problem, and more of a roll axis problem. I built the rig about 4 years ago and have been dealing with it, but if I can make it better I want to. Now that I have a better idea of a rule of thumb for COG (I never knew it was sprung weight, not total weight, but that makes sense to me) I can plug my numbers in. Gotta climb under there with a tape measure and notebook.

Now as far as my 3rd link up front... I was pretty limited in placement options, so I just put it where I could, and gave it as much vertical separation as I could. In fact at full stuff it just barely touches my floorboard. However I do not think it is the source of the problem, because it seems to roll the worst in 2wd, low range.

To be honest I never really thought it was my AS, I just read recently that it can cause a torque roll problem. My AS seems to be excellent otherwise, as it does not squat or lift under power. It just rotates. It has also been suggested that if I double triangulate the rear it should eliminate the problem entirely. I'll look and see if that will be an option while I'm under there.

A lot of people are telling me to just install a sway bar, and if I run out of options maybe I will. But I would rather address the root of the problem and not band-aid it. In the end it will make a better rig, and make me a better builder.

COG can be measured with scales, but a good guess will be fine as well. Going for the top bolt of the bellhousing can work as long as you are not loaded down with stuff up top.

The position of the third link and which side it's on, your roll axis slopes, your AS , etc all affect this (FRONT AND REAR). Torque lean can be a thing, and depending on the type of climb you're talking about it can make or break the line. Huge climbs and really offcamber scenarios change the numbers dramatically. That's why when your on a 8' waterfall things get strange and you're numbers are way different than the static model we use to build. Post up the numbers in the 4 link calculator.

It's also good to say that this can be more or less normal, but you want to build to keep it reasonable as geometry can exagerate it.

Also, real world is when you plug all your numbers into the calculator and you may find that it would take a full rework to get everything super happy. Don't fret, theres a shitload of trucks out there like that and they can still do some amazing lines. Sway bars, springs, etc can all help.

 

[Tnsejed]

Sway bars are a tool that should always be an option your toolbox. It's cool to be be able to add rate only during articulation. I can't say that's a solution or not, but they are always an option.

So 2wd only is what you're worried about. There's always going to be some weight transfer during acceleration. But if like you said it just leans, and it's not really weight transfer you're worried about then it could be the Roll Center height versus CG. These points create a moment. You can build to have it minimal, or theoretically even have it reversed, but then driver feedback becomes minimal. AS plays a big roll in all of this as well.

Another thing that plays into this is shock positioning. If the shocks immediately go past 90 degrees during roll then you end up with a regressive spring rate versus roll amount.

 

[crashandburn]

Sway bars are a tool that should always be an option your toolbox. It's cool to be be able to add rate only during articulation. I can't say that's a solution or not, but they are always an option.

So 2wd only is what you're worried about. There's always going to be some weight transfer during acceleration. But if like you said it just leans, and it's not really weight transfer you're worried about then it could be the Roll Center height versus CG. These points create a moment. You can build to have it minimal, or theoretically even have it reversed, but then driver feedback becomes minimal. AS plays a big roll in all of this as well.

Another thing that plays into this is shock positioning. If the shocks immediately go past 90 degrees during roll then you end up with a regressive spring rate versus roll amount.

Sway bars are a tool that should always be an option your toolbox. It's cool to be be able to add rate only during articulation. I can't say that's a solution or not, but they are always an option.

So 2wd only is what you're worried about. There's always going to be some weight transfer during acceleration. But if like you said it just leans, and it's not really weight transfer you're worried about then it could be the Roll Center height versus CG. These points create a moment. You can build to have it minimal, or theoretically even have it reversed, but then driver feedback becomes minimal. AS plays a big roll in all of this as well.

Another thing that plays into this is shock positioning. If the shocks immediately go past 90 degrees during roll then you end up with a regressive spring rate versus roll amount.

Since posting this I have tried a few things. I moved my lower links inboard 7" and that did help some, but not nearly enough. I tried this because 7" put my roll axis inclination at about 0. I went from 14 degrees of body roll to about 9 or 10. I then tried moving them inboard an additional 6", but that made the problem worse, so I put it back to the 7" position. I raised my uppers 3.5", then 7". According to the spreadsheet, that should have brought my roll axis considerably closer to the COG, but it did nothing to help the problem so I went back to 3.5" for an AS of 88%. To be clear, I have the problem in 2wd and 4wd, it is just worse (therefore most measureable) when in 2wdLo. I've had my AS at 53, 88, and 104%.
I don't see a way to attach my spreadsheet on here. You mentioned shock placement. Mine are perpendicular to the ground. Would that make that much of a difference? How much angle do they need to be set at?

One other thing you mentioned was my front upper link. It is on the drivers side since my driveshaft and exhaust are on the passenger. Not sure if that matters.

I notice you are right up in Florrissant. Could I buy you a coffee or beer and sit down to discuss?

 

[ktmoutfront]

Your upper link will cause one side to roll that direction easier. With a full boddy truck, with lift, you are only going to find a happy medium. It will never be perfect. Can it get better possibly. Mine scrapes the door handles going around a corner fast. No anti-sway bars. I have wheeled the living daylights out of it. Found its limits and stopped doing that.

As anyone on here can attest, I am supper easy on my truck.

 

[crashandburn]

Your upper link will cause one side to roll that direction easier. With a full boddy truck, with lift, you are only going to find a happy medium. It will never be perfect. Can it get better possibly. Mine scrapes the door handles going around a corner fast. No anti-sway bars. I have wheeled the living daylights out of it. Found its limits and stopped doing that.

As anyone on here can attest, I am supper easy on my truck.

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Wade, I've wheeled with you before and I know you aren't kidding. Remember the day at Rainbow falls when you caught a tree stump and got a flat? I was in your passenger seat. Also your alternator was putting like 18 volts and cooking your battery. Then I lost a bolt in my steering but you had one. At the time I had a red and white 2 door S10 Blazer on 40s. I cut that apart and built my 4 door.

Come to think of it, the 2 door had radius arms in it. I did not do the suspension work in that one, I bought the chassis that way and body swapped it. I don't remember having the issue with the 2 door, but it was also on coil springs. I hated the way it would teeter when flexed out because the springs would float at full droop. That's why I went in a different direction when I built the 4 door. The radius arms flexed just fine, I had over 4 feet of total articulation. Should I go back to radius arms? I have my front upper link on my driver side.

 

[ktmoutfront]

Wade, I've wheeled with you before and I know you aren't kidding. Remember the day at Rainbow falls when you caught a tree stump and got a flat? I was in your passenger seat. Also your alternator was putting like 18 volts and cooking your battery. Then I lost a bolt in my steering but you had one. At the time I had a red and white 2 door S10 Blazer on 40s

I do not remember that at all, but it's not surprising with my brain. Did we have fun? That's all that matters.

 

[crashandburn]

I do not remember that at all, but it's not surprising with my brain. Did we have fun? That's all that matters.

We did have fun. At the end of it you said "nice to run an easy trail once in a while and break shit all day", after we ran an easy trail but still broke shit all day.

Anyway, do you think my 3rd link being on the driver side is the issue? Should I go back to radius arms?

Edit: it wasn't a stump, it was a root. We were in a part where the trail had walls of dirt on each side with some roots sticking out.

 

[ktmoutfront]

I vaguely remember that.

Radius arms will help a little.