Four Link Lower Horizontal Separation

busteddodge

busteddodge

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Joined
Jul 12, 2022
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5352
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21
I'm setting up the four link geometry on the rear of a tube buggy. I'm concerned about the lower link chassis side horizontal separation. As it sits now, there is only 10.5" of separation between the chassis side lower link mounts. The upper link mounts are taking a lot of real estate. I've made the uppers adjustable so that I'll be able to tune in some anti-squat.

What happens when the lower link horizontal separation is short? How does it affect body roll or stability? Any difference?

With the uppers at the lowest adjustment, I'm getting about 80% anti-squat when using the four link calculator. The upper and lower links are very close to each other in that position at ride height. Any concerns there?

Let me know what you guys think. Thanks.

topDown.jpeg
sideView.jpeg
clearance.jpeg
 
Someone smart will say things. Lots of different variables but I have my lowers cranked in as far as possible and think it handles really well actually. But I had lots of people say it would be horrible.

upload_2023-6-3_17-16-49-jpg.jpg
 
The historical answer is that people report the rig feeling more stable when they increase the horizontal spacing.

Regarding antis, which calculator version are you using? I would highly recommend against having the uppers so close to being in line with the lowers in the side view. Dang near radius arm behavior.

Is the second picture at expected ride height?
 
Treefrog said:
The historical answer is that people report the rig feeling more stable when they increase the horizontal spacing.

Regarding antis, which calculator version are you using? I would highly recommend against having the uppers so close to being in line with the lowers in the side view. Dang near radius arm behavior.

Is the second picture at expected ride height?
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Yeah, the second picture is at expected ride height. I couldn’t get the calculator to give me anything above 80% anti squat unless I move to the upper way down. I have a 41 inch tall center of gravity so that affects it a lot I think.

I believe I’m using the latest version. I have a couple of posts on the “how’s my numbers“ thread that are pretty recent.
 
snivilous said:
Someone smart will say things. Lots of different variables but I have my lowers cranked in as far as possible and think it handles really well actually. But I had lots of people say it would be horrible.

upload_2023-6-3_17-16-49-jpg.jpg
Click to expand...
Man that upper link is crazy cool. I’ve never seen that. Nice work.
 
busteddodge said:
Man that upper link is crazy cool. I’ve never seen that. Nice work.
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Thanks! As with yours, everything is a compromise. In my case I wanted trailing arms and where the chassis rails were forced the shocks in really far, and that made it so the upper links couldn't go where I wanted without "kinking" them around the shocks. I'd rather have a normal 4 link, but the "Wishbone" or "Y link" upper has worked well.
 
busteddodge said:
Yeah, the second picture is at expected ride height. I couldn’t get the calculator to give me anything above 80% anti squat unless I move to the upper way down. I have a 41 inch tall center of gravity so that affects it a lot I think.

I believe I’m using the latest version. I have a couple of posts on the “how’s my numbers“ thread that are pretty recent.
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Sorry. I do not keep track of who has posted in that thread.

I think you may be over estimating the cg height some.

Do keep in mind that you had the calculator set for 50% drive bias. So any AS value would be half of what it would be in the 3.0 version that was the main stay on PBB. The antisquat suggestions that were common on PBB were based on the older version's 100% rwd assumption.

If you do want to run a higher anti, moving the frame lowers up a little can get a little bit more. There is nothing requiring the lower points to be as close to the belly as possible.
 
Treefrog said:
Sorry. I do not keep track of who has posted in that thread.

I think you may be over estimating the cg height some.

Do keep in mind that you had the calculator set for 50% drive bias. So any AS value would be half of what it would be in the 3.0 version that was the main stay on PBB. The antisquat suggestions that were common on PBB were based on the older version's 100% rwd assumption.

If you do want to run a higher anti, moving the frame lowers up a little can get a little bit more. There is nothing requiring the lower points to be as close to the belly as possible.
Click to expand...
Hey, thanks. I just checked on the version. I’m using 6.10. I think that means that the squat numbers are correct at 50% drive bias, right?

I’m trying to maintain some other advice I read about keeping the lowers as flat as possible. I could move them up like you are saying, but they will crash against the upper links at the moment. If I move the upper links up, I get lower anti-squat.

I can move the upper Link chassis mounts about an inch and a half further outboard and that will give me a little more room for the horizontal separation of the lower links, but I still don’t think I’ll be able to move the links up much without hitting the uppers.
 
busteddodge said:
Hey, thanks. I just checked on the version. I’m using 6.10. I think that means that the squat numbers are correct at 50% drive bias, right?

I’m trying to maintain some other advice I read about keeping the lowers as flat as possible. I could move them up like you are saying, but they will crash against the upper links at the moment. If I move the upper links up, I get lower anti-squat.

I can move the upper Link chassis mounts about an inch and a half further outboard and that will give me a little more room for the horizontal separation of the lower links, but I still don’t think I’ll be able to move the links up much without hitting the uppers.
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I would not have your uppers get so low. The flat as possible advice is focused more on the go fast crowd. For a crawler, especially an east coast one, I would not emphasize that as much.
 
Treefrog said:
I would not have your uppers get so low. The flat as possible advice is focused more on the go fast crowd. For a crawler, especially an east coast one, I would not emphasize that as much.
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Thanks. I have found when I’m reading forum posts and suspension information online, it’s hard to tell what the poster or author is going for. Usually I’m not sure if what I’m reading is geared towards slow crawling or desert racing. This helps a lot. I’m going to go back to the spreadsheet and raise the chassis side lower links to see how that affects anti squat. I’m looking for around 50-100% if I can get there.

IMG_7560.jpeg
 
busteddodge said:
Thanks. I have found when I’m reading forum posts and suspension information online, it’s hard to tell what the poster or author is going for. Usually I’m not sure if what I’m reading is geared towards slow crawling or desert racing. This helps a lot. I’m going to go back to the spreadsheet and raise the chassis side lower links to see how that affects anti squat. I’m looking for around 50-100% if I can get there.

IMG_7560.jpeg
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With a drive bias of 50%, 25-50 is the same suspension as 50-100 if you are following older advice from PBB or similar.
 
Treefrog said:
With a drive bias of 50%, 25-50 is the same suspension as 50-100 if you are following older advice from PBB or similar.
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Is that true even with the newer version of the spreadsheet? I thought that error was taken care of with the newer version?
 
Have you tried cycling the suspension through articulation yet? In the side view picture it looks like your upper and lower links will hit each other.

Also, what is your convergence angle of the lowers?
 
gt1guy said:
Have you tried cycling the suspension through articulation yet? In the side view picture it looks like your upper and lower links will hit each other.

Also, what is your convergence angle of the lowers?
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Not yet. Still making mounts. I’m a little worried about that too.

The angle on the lowers is something like 37 degrees
 
IMG_5195.jpeg

It might the funny angle of the picture.. Doesn’t look like there’s enough room to remove that bolt.
 
McBastard79 said:
IMG_5195.jpeg

It might the funny angle of the picture.. Doesn’t look like there’s enough room to remove that bolt.
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Yeah. Looks like I F$cked up! Haha. The lowers aren’t tacked on yet here. The stacked washers look ridiculous too, but I have nylon lock nuts that I didn’t want to wear out during this mock up phase.
 
Treefrog said:
Quite the opposite. It was a feature added when the front and rear were put on the same sheet.
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Thanks for the explanation here. With all of the advice I’ve gotten from you I feel I owe you several beers.

Just so I make sure I’m getting this right, in version 6, with a drive bias of 50%, an anti-squat calculation of 80% would result in a chassis that behaves like a 2wd car with an antisquat calc of 160%?
 
busteddodge said:
Not yet. Still making mounts. I’m a little worried about that too.

The angle on the lowers is something like 37 degrees.
Click to expand...

Ya, I'd cycle it as soon as you can. When you stuff one wheel, the lower will move up waaaay more than the upper will. And very likely the upper isn't going to move up at all, given that where the uppers mount on the axle is where the axle is pivoting around


busteddodge said:
Thanks for the explanation here. With all of the advice I’ve gotten from you I feel I owe you several beers.

Just so I make sure I’m getting this right, in version 6, with a drive bias of 50%, an anti-squat calculation of 80% would result in a chassis that behaves like a 2wd car with an antisquat calc of 160%?
Click to expand...
No. In that case (50% bias/80%AS) you will have 80%AS in the rear WHEN YOU ARE IN 4WD. When you're in 2WD (100% bias), the rear will have 160%AS.
So it's not a case of "will behave like", it's 2 different cases of "will be". If you're NEVER going to be in 2WD, it isn't a issue. But, 160%AS in 2WD will have some very undesirable side effects.
 
gt1guy said:
Ya, I'd cycle it as soon as you can. When you stuff one wheel, the lower will move up waaaay more than the upper will. And very likely the upper isn't going to move up at all, given that where the uppers mount on the axle is where the axle is pivoting around



No. In that case (50% bias/80%AS) you will have 80%AS in the rear WHEN YOU ARE IN 4WD. When you're in 2WD (100% bias), the rear will have 160%AS.
So it's not a case of "will behave like", it's 2 different cases of "will be". If you're NEVER going to be in 2WD, it isn't an issue. But, 160%AS in 2WD will have some very undesirable side effects.
Click to expand...
Ahhhhhh! Thanks. When explained that way, it makes sense. Thanks for breaking it down.
 
gt1guy said:
Ya, I'd cycle it as soon as you can. When you stuff one wheel, the lower will move up waaaay more than the upper will. And very likely the upper isn't going to move up at all, given that where the uppers mount on the axle is where the axle is pivoting around
Click to expand...
I agree except for that last part. I strongly disagree with that last part. But I would rather not derail this thread.
gt1guy said:
No. In that case (50% bias/80%AS) you will have 80%AS in the rear WHEN YOU ARE IN 4WD. When you're in 2WD (100% bias), the rear will have 160%AS.
So it's not a case of "will behave like", it's 2 different cases of "will be". If you're NEVER going to be in 2WD, it isn't a issue. But, 160%AS in 2WD will have some very undesirable side effects.
Click to expand...
You explained that better than I would have.:beer:
 
Treefrog said:
I agree except for that last part. I strongly disagree with that last part. But I would rather not derail this thread.
Click to expand...

Hey, you're Treefrog, you have to be accurate........................ I'm not bound to any level of intelligence:flipoff2:
 
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