How's my numbers?

[YellowTurtle]

Yep, both at same time. I didn't drive it before switching ends because... delayed gratification.

All arms 25-26" (so 1 spare works), 3 link front, double triangulated rear, tried to keep lower arms flat and tucked up for clearance+good numbers. The only unusual aspect is the narrow ends of rear triangles have some horizontal separation because of packaging, but have more than enough triangulation between upper+lower. Only other change was rear spring mount moved.

TJ with about 3-3.5" lift over stock. Outboarded shock in rear end extended shock tower in front, but already had that with short arms.

As an update:

Recap: on my TJ I'm running rear double triangulated and front 3 link. Has around 3-4deg roll understeer in front and a couple deg roll understeer in back. Overall, chassis had roll oversteer per calc. Been fighting wobbly/oscillating/roll oversteer feeling since out the links on.

I straightened out the rear lowers so now they have about 13deg of angle total (previously had about 40deg) and the uppers stayed the same at 35ish deg total. Calc says this changed the roll understeer in the rear to 1-2deg of rear roll oversteer, and also made the total chassis have more oversteer. It drives much much better than before. Maybe not 100% perfect but a significant difference and much more relaxing to drive.

 

[Treefrog]

As an update:

Recap: on my TJ I'm running rear double triangulated and front 3 link. Has around 3-4deg roll understeer in front and a couple deg roll understeer in back. Overall, chassis had roll oversteer per calc. Been fighting wobbly/oscillating/roll oversteer feeling since out the links on.

I straightened out the rear lowers so now they have about 13deg of angle total (previously had about 40deg) and the uppers stayed the same at 35ish deg total. Calc says this changed the roll understeer in the rear to 1-2deg of rear roll oversteer, and also made the total chassis have more oversteer. It drives much much better than before. Maybe not 100% perfect but a significant difference and much more relaxing to drive.

Great to hear an update. It is awesome to here about how the driving characteristics changed.

Are you able to share the new chassis roll axis? And ae you willing to share what is still not 100% perfect? It seems that I have geometry numbers from the before, even though I cannot find where I got those from. Are you willing to share the after so I can do some side by side comparison?

I am trying to close the loop handing characteristics and 3d performance.

 

[Ghetto Fab.]

As an update:

Recap: on my TJ I'm running rear double triangulated and front 3 link. Has around 3-4deg roll understeer in front and a couple deg roll understeer in back. Overall, chassis had roll oversteer per calc. Been fighting wobbly/oscillating/roll oversteer feeling since out the links on.

I straightened out the rear lowers so now they have about 13deg of angle total (previously had about 40deg) and the uppers stayed the same at 35ish deg total. Calc says this changed the roll understeer in the rear to 1-2deg of rear roll oversteer, and also made the total chassis have more oversteer. It drives much much better than before. Maybe not 100% perfect but a significant difference and much more relaxing to drive.

So you increased roll oversteer in the rear and it now drives better? Out of curiosity what did the rear AS do with that change if it changed at all.

 

[YellowTurtle]

I will attach photos with the new numbers.

Originally I kept the lowers in the same orientation but I lowered the frame side mount 1.75 in. It seemed to help the handling characteristics a little, it definitely hoped the ride quality noticeably, but I still couldn't drive with the sway bar unlocked on a rough street that pitches you side to side (The sway bar has a street mode and an off-road mode when unlocked, that is equivalent to a curry anti-rock). On the street, with the sway bar unlocked, I would still get a lot of the push side to side roll steer-type feeling.

I then straightened out the lower arms as much as I could realistically, they still have approximately 13 1/2 to 14° of separation. The handling improved significantly, the anti-squat stayed the same. I've been driving with the sway bar unlocked on the same roads I commute on every day, and have no issues driving unlocked with the current setup. I still feel a very small amount of the steering reacting to bumps on the road, pushing side to side with one-sided bumps, but realize that it could be a separate issue and I will look into play in my steering and steering box that may have developed in the last few years while hunting other problems.

Previously I had a little over 2° of roll understeer in the rear, almost 4° of rollunder steer in the front, but the body roll axis angle was still considered oversteer. The front is now the same but the rear has a little bit of roll oversteer with the new setup, and the total body roll axis has more total oversteer than before, but this setup drives much better.

 

[YellowTurtle]

I just started to think that if the front has understeer, it will steer toward the direction of the lean, while the rear with understeer will steer away from the lean. So I wondered if those sensations were fighting each other too much when combined.

And the feeling I've been chasing was that when I would lean right, the jeep would nudge to the left and vise versa, which is exactly what rear understeer would seem to cause, and kinda exaggerates the forces/motion felt when the jeep leans side to side from hitting a bump, making the ride very busy and annoying. So I thought I'd try to get less understeer in the rear to see what happened. I have multiple mounts tacked in right now where I can move the rear lowers around to test, and straightening the lowers to take away understeer, and having the lower AS has been a clear winner so far, and definitely worth some lost clearance.

 

[Treefrog]

I will attach photos with the new numbers.

Originally I kept the lowers in the same orientation but I lowered the frame side mount 1.75 in. It seemed to help the handling characteristics a little, it definitely hoped the ride quality noticeably, but I still couldn't drive with the sway bar unlocked on a rough street that pitches you side to side (The sway bar has a street mode and an off-road mode when unlocked, that is equivalent to a curry anti-rock). On the street, with the sway bar unlocked, I would still get a lot of the push side to side roll steer-type feeling.

I then straightened out the lower arms as much as I could realistically, they still have approximately 13 1/2 to 14° of separation. The handling improved significantly, the anti-squat stayed the same. I've been driving with the sway bar unlocked on the same roads I commute on every day, and have no issues driving unlocked with the current setup. I still feel a very small amount of the steering reacting to bumps on the road, pushing side to side with one-sided bumps, but realize that it could be a separate issue and I will look into play in my steering and steering box that may have developed in the last few years while hunting other problems.

Previously I had a little over 2° of roll understeer in the rear, almost 4° of rollunder steer in the front, but the body roll axis angle was still considered oversteer. The front is now the same but the rear has a little bit of roll oversteer with the new setup, and the total body roll axis has more total oversteer than before, but this setup drives much better.

Awesome. Before, after, and middle step. With behavior change. Any chance I could get you to share the top of the calculator with the link end points?

If you share the two points for the drag link as well, I can give you some info on the presence of bump steer.

 

[YellowTurtle]

Here you go. Have 2 picture to show the screen as much as I can.

The 1st 2 are when I only lowered the rear lower frame mounts to get the AS down. The last 2 pics are after I straightened the lowers out a bunch.

 

[Treefrog]

Here you go. Have 2 picture to show the screen as much as I can.

The 1st 2 are when I only lowered the rear lower frame mounts to get the AS down. The last 2 pics are after I straightened the lowers out a bunch.

Well, the 3d results are not as clear cut as I was hoping. Looking at the axle steer as it flexes and how the center of the axle moves as it cycles. Front first. Suspension travel was solved for the lower links.

 

[YellowTurtle]

Can you summarize the implications of your graphs?

 

[Treefrog]

Can you summarize the implications of your graphs?

I am not sure. My best guesses are that the rear doesn't try to steer as much as before in roll. Or it tries to turn with roll instead of crab.

 

[gt1guy]

I think some of the confusion might be coming from the fact that YellowTurtle (or all of us for that matter) isn't driving his rig right up to the limit of where most under/over steer wants to show itself.

If looking at road manners, it's probably best to just ignore anything more than a couple inches of travel.

 

[ditcherman]

First off, thanks to all and especially Treefrog for this thread and all the advice!

I've read and studied this whole thread, and read the bible and just like the other one there are parts where my eyes glaze over (The calculus is like Leviticus to me) but man I'm trying.

Never done anything like this before but I'm building a 4 door FJ40 with an Aqualu aluminum tub and a hardtop, on '78 (kingpin) Ford Dana 60's on a 89 Superduty frame.
I'm going with links to try to lower the beast from the original springs, and to try to build flex in the suspension instead of letting the frame crack my tub. Oh it's got a Cummins 12v mechanical in it so pretty heavy up front. NV4500.

Planning on at least 37" tires. Needs to have good highway/interstate manners to get me to the trails, mostly trail rig but if I can rock climb with it that'd be cool too.

3 link up front and 4 in the back. Willing to do what it takes to do this right, but things seem tight up front.
My problem is when I get to decent anti numbers along with pinion change my oversteer numbers are pretty bad for the highway. If I fix oversteer by dropping the frame end of the front lower link the front AD/AL numbers go to pot and I'm not particularly happy with the pinion travel.

I'm also very concerned about the forces I'm seeing on the 3 link. I'm confident in my welding but I'd rather not have to build to that, top link can't go up much. I can lower lower links at axle but sacrifice clearance.

Also, how concerned do I need to be with the very bottom graph, roll centers as % of travel? Haven't seen that discussed.

Am I missing something easy?
Thanks in advance!

Here's what I come up with with the antis and pinion travel good but terrible oversteer...

And here's where I can see how to "fix" the oversteer but the antis are ugly and the forces are still bad.

 

[Treefrog]

First off, thanks to all and especially Treefrog for this thread and all the advice!

I've read and studied this whole thread, and read the bible and just like the other one there are parts where my eyes glaze over (The calculus is like Leviticus to me) but man I'm trying.

Never done anything like this before but I'm building a 4 door FJ40 with an Aqualu aluminum tub and a hardtop, on '78 (kingpin) Ford Dana 60's on a 89 Superduty frame.
I'm going with links to try to lower the beast from the original springs, and to try to build flex in the suspension instead of letting the frame crack my tub. Oh it's got a Cummins 12v mechanical in it so pretty heavy up front. NV4500.

Planning on at least 37" tires. Needs to have good highway/interstate manners to get me to the trails, mostly trail rig but if I can rock climb with it that'd be cool too.

3 link up front and 4 in the back. Willing to do what it takes to do this right, but things seem tight up front.
My problem is when I get to decent anti numbers along with pinion change my oversteer numbers are pretty bad for the highway. If I fix oversteer by dropping the frame end of the front lower link the front AD/AL numbers go to pot and I'm not particularly happy with the pinion travel.

Are you able to move the frame end of the upper up? The long wheelbase will help dull oversteer's effects on the highway.

I'm also very concerned about the forces I'm seeing on the 3 link. I'm confident in my welding but I'd rather not have to build to that, top link can't go up much. I can lower lower links at axle but sacrifice clearance.

You can likely drop the lower axle .5"-1" without loosing clearance. You will probably end up with a beefy upper mount integrated into the truss.

Also, how concerned do I need to be with the very bottom graph, roll centers as % of travel? Haven't seen that discussed.

I would not worry about it. It might be relevant if you are building a high speed desert car. It was more of a look at how the front and rear are relative to each other. In your case, if you are going a bit faster down rough roads and have shocks that will cause it to ride higher than it sits, the vehicle roll slope will flatten out.

Am I missing something easy?
Thanks in advance!

Here's what I come up with with the antis and pinion travel good but terrible oversteer...


And here's where I can see how to "fix" the oversteer but the antis are ugly and the forces are still bad.

In the rear, I would recommend targeting a slightly flatter roll slope. Moving the axle uppers as close together as you can get away with. Moving the axle lowers up and the upper frames down will help while not hurting the antisquat too much.

 

[ditcherman]

Are you able to move the frame end of the upper up? The long wheelbase will help dull oversteer's effects on the highway.

You can likely drop the lower axle .5"-1" without loosing clearance. You will probably end up with a beefy upper mount integrated into the truss.

I would not worry about it. It might be relevant if you are building a high speed desert car. It was more of a look at how the front and rear are relative to each other. In your case, if you are going a bit faster down rough roads and have shocks that will cause it to ride higher than it sits, the vehicle roll slope will flatten out.

In the rear, I would recommend targeting a slightly flatter roll slope. Moving the axle uppers as close together as you can get away with. Moving the axle lowers up and the upper frames down will help while not hurting the antisquat too much.

Thanks so much!
I'll do some more measuring and work on those suggestions.

 

[YellowTurtle]

In the rear, I would recommend targeting a slightly flatter roll slope. Moving the axle uppers as close together as you can get away with. Moving the axle lowers up and the upper frames down will help while not hurting the antisquat too much.

I would like to hear more on this subject. What real world effect would you observe by moving the axle uppers closer to flatten the roll slope? I'd be interested in low speed and high effects. Thanks.

 

[endless CJ]

Just about to start burning mounts in place. I think I'm happy enough with the rear, i can move the frame mounts down about 1.5 inches, and i could spread the upper axle mounts out a little if there is some advantage. axle lowers are no longer moving without a plasma cutter...

Up front of course packaging is the issue. i can move the lower frame mounts around a little in all directions, but not seeing any change in roll slope. I'm assuming i want to get closer to 0 or less at ride height. appreciate any recommendations.

cj7 aluminum body, 5.3 LMG, needs to be streetable to get to the fun stuff...

Thanks,

 

[Treefrog]

Just about to start burning mounts in place. I think I'm happy enough with the rear, i can move the frame mounts down about 1.5 inches, and i could spread the upper axle mounts out a little if there is some advantage. axle lowers are no longer moving without a plasma cutter...

Up front of course packaging is the issue. i can move the lower frame mounts around a little in all directions, but not seeing any change in roll slope. I'm assuming i want to get closer to 0 or less at ride height. appreciate any recommendations.

cj7 aluminum body, 5.3 LMG, needs to be streetable to get to the fun stuff...

Thanks,

Regarding the rear, decreasing the antis some will help. As it is now, in 2wd, you will be right at 100% anti. And as the axle moves up and down, it will switch between squat and anti squat tendencies.

In the front, it may be worth looking more into which side the upper is mounted on. A good place to start that is to look into no torque roll with 3 links.

You may want to tend towards more understeer; a short wheelbase rig is more sensitive to it.

 

[Treefrog]

I would like to hear more on this subject. What real world effect would you observe by moving the axle uppers closer to flatten the roll slope? I'd be interested in low speed and high effects. Thanks.

Without running a more in depth analysis, I am inclined to say the only really noticeable effects are to change the roll slope, roll center, and pinion angle in flex. Typically close together uppers will result in less movement of the roll center in relation to the axle. I have found that most of the flex behavior is usually governed by the lower links in the typical rock crawler 4 link setup.

 

[YellowTurtle]

Without running a more in depth analysis, I am inclined to say the only really noticeable effects are to change the roll slope, roll center, and pinion angle in flex. Typically close together uppers will result in less movement of the roll center in relation to the axle. I have found that most of the flex behavior is usually governed by the lower links in the typical rock crawler 4 link setup.

What about at speed? Crawling feels great. 15-45/50 mph what has always been obnoxious. The 1 most suspicious element in my setup is the rear upperscdontcmeet at the axle (there's enough triangulation but they are mid arms so less length than normal). I'm open to redoing my upper axle mounts if there would be some benefit.

 

[Treefrog]

What about at speed? Crawling feels great. 15-45/50 mph what has always been obnoxious. The 1 most suspicious element in my setup is the rear upperscdontcmeet at the axle (there's enough triangulation but they are mid arms so less length than normal). I'm open to redoing my upper axle mounts if there would be some benefit.

For your setup, narrowing the uppers would increase the roll slope, but would still decrease the range of travel of the roll center. The behavior while going slow should be similar to when going faster, but the suspension is likely more active with the higher speed.

 

[ditcherman]

I searched but didn’t find it…
Wondering about the Link Sizing page, I have mostly low numbers in there, and they are a mix of pink and green.
I’m wondering what the numbers represent and if I should trust them.
I have traced to the Calculations page but can’t make sense of that either.

I am planning on using 2 x .250 DOM and have that entered in.

 

[Treefrog]

I searched but didn’t find it…
Wondering about the Link Sizing page, I have mostly low numbers in there, and they are a mix of pink and green.
I’m wondering what the numbers represent and if I should trust them.
I have traced to the Calculations page but can’t make sense of that either.

I am planning on using 2 x .250 DOM and have that entered in.

Green means that it is above the desired factor of safety (FS) for that loading condition. Pink is below. The highest force seen in the link is used where relevant. The default FS target numbers came from AZRockCrawler.com, which is no longer around.

I cannot speak on if the link size you have chosen is correct for the application.

 

[ditcherman]

Green means that it is above the desired factor of safety (FS) for that loading condition. Pink is below. The highest force seen in the link is used where relevant. The default FS target numbers came from AZRockCrawler.com, which is no longer around.

I cannot speak on if the link size you have chosen is correct for the application.

OK thanks, that makes sense to me, what doesn't make sense to me is why the numbers would change if they are forces, when you change the size of the link, or the material.
I'l look into it further.

I've done lots of measuring and some rearranging and am very happy with the numbers, getting very close to getting it together.

 

[Treefrog]

OK thanks, that makes sense to me, what doesn't make sense to me is why the numbers would change if they are forces, when you change the size of the link, or the material.
I'l look into it further.

I've done lots of measuring and some rearranging and am very happy with the numbers, getting very close to getting it together.

It is a ratio of the force present to the max force the link can take.

 

[DocRamsay]

Here we go. Oh grand frog, grant me thy wisedom and knowledge of all things suspension-y. First gen xtra cab tacoma, LS/4L80 powered, goal is to have fun in rocks desert and snow.

Pinion change is looking not happy, I kinda feel like everything else is fine. I feel like I'm chasing numbers on a page at this point.

 

[Treefrog]

Here we go. Oh grand frog, grant me thy wisedom and knowledge of all things suspension-y. First gen xtra cab tacoma, LS/4L80 powered, goal is to have fun in rocks desert and snow.

Pinion change is looking not happy, I kinda feel like everything else is fine. I feel like I'm chasing numbers on a page at this point.

It sure does feel like chasing numbers, like a dog chasing its tail.

Antis are too high for the application. Lower links are likely going to be 8"-15" too long, front and rear. Fixing that should help with the pinion angles.

You may want to look at the driveshaft page as well. It can help with how much is too much change. The pitch page may provide some insight into the front caster angle change.

The panhard is attached to the frame on driver right and the axle on driver left. Do you have it backwards? If possible you will likely want the upper link on driver left.

You probably want even up/down travel in the front, but slightly biased for up travel isn't the end of the world for something that might see speed.

Is the rear a trailing arm?

You will probably want a bit more angle between the lowers, front and rear. I have read that it helps to have it so the links do not angle inward when there is uneven travel. Watch for tire turning clearance up front.

The CG looks like it may be a couple inches high.

The axle roll slopes are not going to be speed friendly. More lower (and less rear upper) angle should help. Chassis is pretty good.

 

[DocRamsay]

It sure does feel like chasing numbers, like a dog chasing its tail.

Antis are too high for the application. Lower links are likely going to be 8"-15" too long, front and rear. Fixing that should help with the pinion angles.

You may want to look at the driveshaft page as well. It can help with how much is too much change. The pitch page may provide some insight into the front caster angle change.

The panhard is attached to the frame on driver right and the axle on driver left. Do you have it backwards? If possible you will likely want the upper link on driver left.

You probably want even up/down travel in the front, but slightly biased for up travel isn't the end of the world for something that might see speed.

Is the rear a trailing arm?

You will probably want a bit more angle between the lowers, front and rear. I have read that it helps to have it so the links do not angle inward when there is uneven travel. Watch for tire turning clearance up front.

The CG looks like it may be a couple inches high.

The axle roll slopes are not going to be speed friendly. More lower (and less rear upper) angle should help. Chassis is pretty good.

Rear trailing arms, I'm guessing at a lot of it until it can all sit in the shop with the axles actually under the truck. I set the frame at 20" and got some of those frame numbers after adding 2" and didn't fuck with the driveshaft tab at all.

Lowers to the inside of the frame up front. Shortened the uppers in back. I'm not totally locked into the 49" trailing arms, laser guy hasn't gotten back to me about when he can cut them, but I'd like to not have to shorten them.

Good lookin out on the panhard, fixed.

 

[ditcherman]

Rear trailing arms, I'm guessing at a lot of it until it can all sit in the shop with the axles actually under the truck. I set the frame at 20" and got some of those frame numbers after adding 2" and didn't fuck with the driveshaft tab at all.

Lowers to the inside of the frame up front. Shortened the uppers in back. I'm not totally locked into the 49" trailing arms, laser guy hasn't gotten back to me about when he can cut them, but I'd like to not have to shorten them.

Good lookin out on the panhard, fixed.

Ok first off i'm new here and new to all this but am totally immersing myself in all things suspension, to get mine built, and am reading everything I can. So I have a couple questions about your setup...

The first thing that struck me was your front travel, and your front axle end link separation and wondering of you can really get that 12" of link separation packaged? I did see you were on 42's so maybe you can. This is where my struggles are, creating some pretty high forces.

Second, your rear convergence angle is already pretty minimal, and you have the rear tops 2.5" apart, can you really get them that close, physically? I assuming this is a 'centerline to link' measurement and that looks tight to me, and could tank your whole setup if not caught before you get stuff cut.

Once again, new to all this, so feel free to ignore me if you think I'm an idiot.

It does feel like chasing numbers, I go lay under mine and measure and come back in and type stuff in, but i know if I had just used my newb logic it would have been a disaster. So I'm still chasing, but confident it's gonna be great.

 

[Treefrog]

Ok first off i'm new here and new to all this but am totally immersing myself in all things suspension, to get mine built, and am reading everything I can. So I have a couple questions about your setup...

The first thing that struck me was your front travel, and your front axle end link separation and wondering of you can really get that 12" of link separation packaged? I did see you were on 42's so maybe you can. This is where my struggles are, creating some pretty high forces.

Second, your rear convergence angle is already pretty minimal, and you have the rear tops 2.5" apart, can you really get them that close, physically? I assuming this is a 'centerline to link' measurement and that looks tight to me, and could tank your whole setup if not caught before you get stuff cut.

Once again, new to all this, so feel free to ignore me if you think I'm an idiot.

It does feel like chasing numbers, I go lay under mine and measure and come back in and type stuff in, but i know if I had just used my newb logic it would have been a disaster. So I'm still chasing, but confident it's gonna be great.

I can probably answer some of this.

His rear uppers are 5 inches apart. The 2.5 is distance from the center line.

3 link setups are slightly easier to package the uppers than a triangulated setup since you are beside the engine. He has some advantage in that his lowers are below the axle tube.

 

[DocRamsay]

Ok first off i'm new here and new to all this but am totally immersing myself in all things suspension, to get mine built, and am reading everything I can. So I have a couple questions about your setup...

The first thing that struck me was your front travel, and your front axle end link separation and wondering of you can really get that 12" of link separation packaged? I did see you were on 42's so maybe you can. This is where my struggles are, creating some pretty high forces.

Second, your rear convergence angle is already pretty minimal, and you have the rear tops 2.5" apart, can you really get them that close, physically? I assuming this is a 'centerline to link' measurement and that looks tight to me, and could tank your whole setup if not caught before you get stuff cut.

Once again, new to all this, so feel free to ignore me if you think I'm an idiot.

It does feel like chasing numbers, I go lay under mine and measure and come back in and type stuff in, but i know if I had just used my newb logic it would have been a disaster. So I'm still chasing, but confident it's gonna be great.

You did get me thinking about lock to lock, granted this thing is massively toe-ed out right now, I grabbed some 2” box and gave it the old community college try. These are 48” long and I’m not tremendously worried about it if I mount them inboard of the frame. I’m chopping the frame at the body mounts anyway, so the rules are made up and the points don’t matter. As long as I can get the driveshaft to work and I’d love to not have to modify the oil pan. Even if I do, I have a sawzall, welders and a sense of adventure (actually if the oil pan starts getting fucked with I’m gonna be real tempted to dry sump it because I’m an idiot and make poor financial decisions).

Treefrog covered the rear uppers. Both axles are already welded up and I’m sure that’s gonna bit me in the ass when I actually start building the truck in 5 years.