How's my numbers?

jku. 43 stickies off road and 40" radials on. setting it up for 90% trail, 10% street. front will be a 3 link (havent input the data yet) but I plan to do the rear first. these measurements make everything fit very nice. planning on 16" coilovers in the rear. 4" up, 12 down. I can't tell how much total angle I have.

Elusive said:

jku. 43 stickies off road and 40" radials on. setting it up for 90% trail, 10% street. front will be a 3 link (havent input the data yet) but I plan to do the rear first. these measurements make everything fit very nice. planning on 16" coilovers in the rear. 4" up, 12 down. I can't tell how much total angle I have.

Click to expand...

Rear looks good for the application. You may want to double check that the rolling radius is correct for the tire size.

You have 58.7 degrees of rear convergence if that is what you mean by angle.

That seems pretty heavy for a JKU. Is it loaded down with steel armor or something?

Treefrog said:

Rear looks good for the application. You may want to double check that the rolling radius is correct for the tire size.

You have 58.7 degrees of rear convergence if that is what you mean by angle.

That seems pretty heavy for a JKU. Is it loaded down with steel armor or something?

Click to expand...

THANK YOU! Jeep has a hemi, 545rfe, SD 60 front 14 bolt rear both with older (heavy) artec trusses. then the bumpers, corner guards, etc. its a sow. I was using those rolling radius numbers for now because...well the 40's are on it and I'm too lazy to bolt the heavy ass stickies on it for measurements. Im thiinking the 43s with 5 pounds of air are close to the same height as the aired up 40 radials. I'll get the 3 link front going.

Hi Treefrog, been doing more reading up and thinking about AS/AD and would appreciate some input on my line of thinking here.

You recommended AS/AD be in the 30-40% ish range for my use type (Highway capable moderate rock crawler on 37s).

Please correct any of my thinking that may be wrong here, but having a below neutral AD (<50% at 50/50 drive bias) in the front will cause the suspension to tend to unload and move the wheels down under traction. So, when trying to climb up a rock or ledge, the suspension will have a tendency to push the wheels down into the rock and move the body up in the front. In some ways this seems like a good idea because it may give the tire more traction, and try keep the tires pushing into the ground on steep climbs, but in other ways opposite of what one would want when rock crawling. In my mind, especially if I an climbing one side and not the other, I would think that I would prefer >50% AD in the front so that the side of the suspension hitting the rock will tend to squat, making use of the uptravel available and allowing the wheel to move up the obstacle without having to push the whole body up right away, which I feel would allow the wheel to roll up stuff more easily and comfortably.

I am also aware that >50% AD makes for better braking performance, and that may just be one of the compromises to make when building a streetable rig.

As for the rear, I would also think having >50% AS would be desirable because on steep climbs or obstacles, the rear wheels pushing down under traction will shift weight onto the front wheels giving them traction, rather than the rear squatting down shifting weight off the front.

I was also wondering more about AS/AD slopes and how opposite sides may interact. You suggest having antis rise with compression, which makes sense to reduce squat and dive more as you approach max compression. But what about drooping out? The way I see it, if you are in a situation such as the video I linked below where you have one side stuffed up and the other side drooped out and you get traction, and your AS curve is such that you have more AS higher up in the suspension travel vs drooped out, the stuffed tire AS will overcome the dropped side AS and push the stuffed tire down as well as the dropped tire up, forcing the body to roll over.



If my thinking there is true, then I would think you would want to make sure the AS curve looks something like this (ignore %, just looking at cure shape):



Where the drooped tire AS will overcome the stuffed tire AS until it has reached a more stable point. If the curve is more of a straight line like " \ " or doesn't curve back over, then the lower tire will always have more AS than the higher one, which may help even more with stability. Maybe?

The same sort of logic applies if we are going with <50% AS in the rear, but with the graph going the opposite way like " / ". If the drooped side has a lower AS then the stuffed side in this situation, then it will want to do the same thing and roll the body over, just that it will moreso be the dropped side pulling it over vs the stuffed side pushing it over. Having the graph go like " \ " in this situation would counteract that, but that is the way people's curves seem to go when building <50% AS anyways. So the main thing there is making sure the AS curve looks like " \ " regardless of whether you are running more or less than 50% AS.

But, what about AS crossing over that 50% mark at some point in the curve? If the curve looks something like this:



then the stuffed and dropped wheels will act oppositely under traction, with the stuffed trying to squat more, and the drooped trying to droop more, which seems to me would be kinda unstable.

However, with a more vertical curve that doesn't cross over the 50% line, then the stuffed and drooped sides wont have too different of AS values and wont be counteracting each other as much. This may be something to shoot for? A relatively vertical AS curve, whether it is more or less than 50%?



I could be seriously overthinking all of this though, as I know a lot of this behavior can be addressed with coilover tuning and sway bars. But seeing videos like this makes me think it can have a pretty big effect.

DirtSniffer said:

Hi Treefrog, been doing more reading up and thinking about AS/AD and would appreciate some input on my line of thinking here.

...

Click to expand...

Alright, some discussion. I'll briefly respond to some of this here, but hopefully it will not be a problem if I take the the more theoretical stuff over to the linked suspension bible thread. But it will take me some time to fully respond to it there.

Short answer:

• Instant center location and the wheel movement arc
• Load transfer from a slope.
• AS changing with load transfer (change in drive bias)
• Vertical, relative to surface, force as AD/AS increases (steeper links)
• Axle in a flexed state changing projected side view links and antis.
• Antis only correlate to actual forces and do not show the full picture.

As for some stuff that is more direct numbers related.

The reason to not design near anti = bias is that in theory small changes in traction and travel cause crossover of between anti-squat and pro-rise. This generally results in hopping. Similar can happen with antis over anti = bias where the instantaneous force from acceleration wears off and with it the pro-rise, causing cyclic traction spikes and hopping.

I'll address the first video more later, but I would suggest looking at how little the drivers front seems to unload as the front pops up. The front was barely, if at all, doing anything.

The second video is a really good example of something that was prevalent in the early linked days but has generally been designed against. The rear is trying to drive under the vehicle as the front applies resistive force, braking in this case.

Newb here. Very green on link suspensions....
How do my numbers look?
fj40 mostly forest roads. Lots of road driving to get to forest roads. Did do fruity pebbles last year by mistake in the Black Hills SD.... But normally not that extreme.

fjdiesel said:

Newb here. Very green on link suspensions....
How do my numbers look?
fj40 mostly forest roads. Lots of road driving to get to forest roads. Did do fruity pebbles last year by mistake in the Black Hills SD.... But normally not that extreme.

Click to expand...

I would recommend aiming for lower antis. and flatter roll slopes. You have quite a bit more rear link convergence than needed. Straightening out the lowers would help with the roll slope.

Treefrog said:

I would recommend aiming for lower antis. and flatter roll slopes. You have quite a bit more rear link convergence than needed. Straightening out the lowers would help with the roll slope.

Click to expand...

We have been looking at redoing his rear 4 link over the last few days. His current setup the lowers are mostly parallel. But leaves in front. Now going 3 link front. The issue we were running into is we cant seem to be able to get the panhard high enough to get a positive understeer body roll axis. Narrowing the rear lower frame mounts helped the most in that regard, but I guess roll slope then suffers.

DirtSniffer said:

We have been looking at redoing his rear 4 link over the last few days. His current setup the lowers are mostly parallel. But leaves in front. Now going 3 link front. The issue we were running into is we cant seem to be able to get the panhard high enough to get a positive understeer body roll axis. Narrowing the rear lower frame mounts helped the most in that regard, but I guess roll slope then suffers.

Click to expand...

Am I reading correctly that you are helping fjdiesel?

You may not be able to get the body axis to understeer. I would try to get the within a few degrees. The real issues come not from it being slightly oversteer, but from it being steep and an unaware or un-attentive driver getting behind the wheel. It is my understanding that car people tend to prefer slight oversteer, but that manufactures prefer slight understeer because it causes less issues with office dad and soccer mom type drivers.

The other aspect of it is that reducing the convergence angle will generally reduce geometric roll steer.

Oversteer and understeer are not purely geometry functions. Things like the springs and anti-roll bars play a big roll as well.


I am still working on the response to your longer post. Some parts of it are making me think a lot more than I was intending to this week.

Treefrog said:

Am I reading correctly that you are helping fjdiesel?

You may not be able to get the body axis to understeer. I would try to get the within a few degrees. The real issues come not from it being slightly oversteer, but from it being steep and an unaware or un-attentive driver getting behind the wheel. It is my understanding that car people tend to prefer slight oversteer, but that manufactures prefer slight understeer because it causes less issues with office dad and soccer mom type drivers.

The other aspect of it is that reducing the convergence angle will generally reduce geometric roll steer.

Oversteer and understeer are not purely geometry functions. Things like the springs and anti-roll bars play a big roll as well.


I am still working on the response to your longer post. Some parts of it are making me think a lot more than I was intending to this week.

Click to expand...

Yes sir, we are building relatively similar FJ40s and live close to each other.

We will take that into consideration and see what we come up with.

Appreciate you taking the time enlightening me, I'm still a ways out from finalizing my frame design and starting to build it and just trying to make sure I have a well thought out design, no rush at all. Thanks again

Treefrog said:

I would recommend aiming for lower antis. and flatter roll slopes. You have quite a bit more rear link convergence than needed. Straightening out the lowers would help with the roll slope.

Click to expand...

Thank you for the feedback!!

Treefrog said:

I would recommend aiming for lower antis. and flatter roll slopes. You have quite a bit more rear link convergence than needed. Straightening out the lowers would help with the roll slope.

Click to expand...

On the topic of roll slopes, what would be a good number to shoot for? Are we mostly concerned with the static height slope, or do we need to try keep the extremes within a certain range?

Something like this look decent? Relatively close to 0 at ride height. But how much change with suspension travel is ok? Or not too important at the slow speeds we would be going when seeing that level of flex, as the slope is more important for road handling?



Thanks for your input on the bible thread, I'll take it into consideration and look forward to anything else you might come up with. I wish there were more people sharing their numbers and videos of their rigs in action to see how their setup works in the real world rather than just saying it "works good". We can theorize all day about what should be best, but seeing it work in the real world could be a different story.

Also FYI, I did notice the graphs for the front have the labels for the top graphs, but rear side does not.

DirtSniffer said:

On the topic of roll slopes, what would be a good number to shoot for? Are we mostly concerned with the static height slope, or do we need to try keep the extremes within a certain range?

Click to expand...

Mostly ride. And close to 0 with negative preferred.

DirtSniffer said:

Something like this look decent? Relatively close to 0 at ride height. But how much change with suspension travel is ok? Or not too important at the slow speeds we would be going when seeing that level of flex, as the slope is more important for road handling?

Click to expand...

Yes. I wouldn't worry much about travel. Typically, roll is going to be with the axle center near ride.

DirtSniffer said:

Thanks for your input on the bible thread, I'll take it into consideration and look forward to anything else you might come up with. I wish there were more people sharing their numbers and videos of their rigs in action to see how their setup works in the real world rather than just saying it "works good". We can theorize all day about what should be best, but seeing it work in the real world could be a different story.

Click to expand...

Discussion and debate is better than just assuming what I ramble about is accurate.

DirtSniffer said:

Also FYI, I did notice the graphs for the front have the labels for the top graphs, but rear side does not.

Click to expand...

Yeah. The rear does, but for some reason they get covered up. Scaling to screen resolutions was done to work. Not done to work properly.

YellowTurtle said:

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.

Click to expand...

In case it helps anyone in the future I wanted to follow up in this.

I have been chasing a weird symptoms, described above, since building my mid-arm setup.

The steering and wheels and tires were the same as before my build so I was suspicious of my geometry/link setup since that's the only thing that changed initially. I tried 2 different steering setups, new ball joints, wheels/tires, new link joints with less deflection, and recently picked up a currie track bar to be able to check that off the suspects. I also replaced my 13yo GoPro with something that had modern resolution and frame rate, which helped me diagnose.

Turns out my setup is just really sensitive to caster, and I've been running too much caster. I was trying 6-9deg, and believed "more=better" like you see all over the internet.

Turns caster down to 4-4.5deg last night and for the first time since my build, it drives straight, even when hitting one sided bumps. No more sway after off-center bumps and no more feeling of the front tires pushing against each other and fighting.

Hope that helps someone.

YellowTurtle said:

In case it helps anyone in the future I wanted to follow up in this.

I have been chasing a weird symptoms, described above, since building my mid-arm setup.

The steering and wheels and tires were the same as before my build so I was suspicious of my geometry/link setup since that's the only thing that changed initially. I tried 2 different steering setups, new ball joints, wheels/tires, new link joints with less deflection, and recently picked up a currie track bar to be able to check that off the suspects. I also replaced my 13yo GoPro with something that had modern resolution and frame rate, which helped me diagnose.

Turns out my setup is just really sensitive to caster, and I've been running too much caster. I was trying 6-9deg, and believed "more=better" like you see all over the internet.

Turns caster down to 4-4.5deg last night and for the first time since my build, it drives straight, even when hitting one sided bumps. No more sway after off-center bumps and no more feeling of the front tires pushing against each other and fighting.

Hope that helps someone.

Click to expand...

Interesting. Mind me asking what size tires and how much toe in you have?

Treefrog said:

Interesting. Mind me asking what size tires and how much toe in you have?

Click to expand...

So I think know what you're thinking, but I'm only running medium size tires that measure out to about 33.5 true height, so it's not like I'm running 42s with exaggerated trail.

When the caster was set higher, and I was fighting the wobble/sway effect, I repeatedly found that a little toe out, 1/8-1/4", made it feel the best. I did blind experiments where I would adjust the toe, without measuring, only keeping track of how many turns I adjusted, and rate what felt best; I always ended up with slight toe out. Any more toe out and it started to wander more that I could tolerate, any toe in and the wobble/tires-fighting-each-other feeling would get much worse.

Now that I'm down to about 4-4.5deg caster, slight toe in drives the best, as you normally expect. So seems like the slight toe out somehow was compensating for the excessive positive caster, I'm not smart enough to figure out how though.

Interestingly my dad was around this weekend and having me help with his rig (samurai still on leafs). His steering felt almost identical to what I've been dealing with. Hitting bump square in was fine off-square bumps caused it to wobble and almost feel like a snowball effect that will just keep worsening unless you countersteer a bit.

After a test drive I measured his caster, set by wedge shims included in his suspension package, and he had +0.5deg of caster. So my jeep with excessive caster of 7-9deg+ felt identical to basically no caster at all.

Anyways it's just interesting and I hope it can help others. I'm seeing more discussions showing up possibly linking death wobble to caster being too high, and I can totally see that now.

Thank you so much for taking time to look.

Elusive said:

Thank you so much for taking time to look.

Click to expand...

Assuming you want feedback on the front?

I would do what you can to get the antis down and pinion angle more constant. Front roll axis slope is not too much of an issue for a mostly trail rig.

You need to get the axle end of the lower links high up. Those will constantly run into rocks.

Thank you. I’ll work on it

in an effort of transparency for all of us to learn.....

Treefrog since our conversation on page 23, I leveled out preload on all corners to take out that variable. That did not help low roll center can not be a the cause for body roll in this case because the body roll is not the same side to side.

The one side leans more when the track bar angle gets steeper. I did some reading on jacking effects and same side track bars are a non issue when your track bar is flat, mine isnt and I think that is what I need to fix.

06h3 said:

in an effort of transparency for all of us to learn.....

Treefrog since our conversation on page 23, I leveled out preload on all corners to take out that variable. That did not help low roll center can not be a the cause for body roll in this case because the body roll is not the same side to side.

The one side leans more when the track bar angle gets steeper. I did some reading on jacking effects and same side track bars are a non issue when your track bar is flat, mine isnt and I think that is what I need to fix.

Click to expand...

Hopefully flattening it works.

Thinking about it again, and looking at your geometry, what I think is happening is that the driver's side high body roll causes the track bar to get steeper, as you point out. With steeper comes the CG moving towards to the downhill side and the component forces wanting to roll the body more.

I think that flipping it side to side would just switch wich off camber side feels sketchy.

We learn more all the time.

Ok, Im welding this up this week. how we looking

Elusive said:

Ok, Im welding this up this week. how we looking

Click to expand...

Front anti might be a bit on the low side. I still think you will run into issues with dragging the axle lower link mounts over everything. Otherwise not too bad. I would double check that the panhard is equal length to the steering linkage; it looks like it might be on the shorter side.

I also just realized that I missed adding some plots, the side to side movement of the panhard. Oops. Hopefully that is not a big deal in the long run.

Thoughts? Newb to rear 4 links. Front 3 link is pretty well in place and can't change to much besides the frame side upper link length and height and even then, it's pretty minimal.

Rear 4 link its pretty wide open. The numbers I listed are the ideal places, but I can narrow or widen the lower links at the frame more and move them up. The upper link at the rear frame can go up and down some but not much more inboard without some crazy braces.

Car is a 4500 car for koh/ultra4 series that will see a bit of regular crawling at sand hollow/rubicon/jv and street driven on occasion. The numbers are how i currently have it set up but overall ride height will probably come down 1.25 inches to even out the front travel, I wont know that till I get it off table/stand I have it on when i turn it around though.

Sorry for the multiple pictures, the calculator loads with the numbers super small at the top for me and only way to zoom in was with the magnifier in the settings on the computer.

rear


front-i forgot to change the up travel number back to 8.75 which is what its setup for now on the stands
Rear antisquat/roll center



front anti dive/roll center

Malburg114 said:

Thoughts? Newb to rear 4 links. Front 3 link is pretty well in place and can't change to much besides the frame side upper link length and height and even then, it's pretty minimal.

Rear 4 link its pretty wide open. The numbers I listed are the ideal places, but I can narrow or widen the lower links at the frame more and move them up. The upper link at the rear frame can go up and down some but not much more inboard without some crazy braces.

Car is a 4500 car for koh/ultra4 series that will see a bit of regular crawling at sand hollow/rubicon/jv and street driven on occasion. The numbers are how i currently have it set up but overall ride height will probably come down 1.25 inches to even out the front travel, I wont know that till I get it off table/stand I have it on when i turn it around though.

Sorry for the multiple pictures, the calculator loads with the numbers super small at the top for me and only way to zoom in was with the magnifier in the settings on the computer.

rear

front-i forgot to change the up travel number back to 8.75 which is what its setup for now on the stands

Rear antisquat/roll center

front anti dive/roll center

Click to expand...

What screen resolution are you running? A super ultrawide?

The antis look slightly low in the rear. I think that moving the axle end of the uppers up a hair would help. The belly height is rather high even if it comes down some. I would think that lowering it a bit would allow for some better geometry and help when racing. It looks like you are planning a wishbone upper in the rear?

Treefrog said:

What screen resolution are you running? A super ultrawide?

The antis look slightly low in the rear. I think that moving the axle end of the uppers up a hair would help. The belly height is rather high even if it comes down some. I would think that lowering it a bit would allow for some better geometry and help when racing. It looks like you are planning a wishbone upper in the rear?

Click to expand...

Not sure on the resolution. Just downloaded the file and opened it. Not a tech person at all.

Axle end uppers can’t really go higher as the mount is already made. It’s only tacd to the axle but I’d really prefer not to remake it again.. what should I be shooting for anti squat wise based off my use? Would moving the frame ends be enough to reach that number. I may be able to move the axle lowers a hair lower depending on when I put it in.

It’ll get lowered some but I won’t know exactly how much till I get a rear axle in it and can jack it up to see true ride height.

Correct on the wishbone.

Malburg114 said:

Not sure on the resolution. Just downloaded the file and opened it. Not a tech person at all.

Axle end uppers can’t really go higher as the mount is already made. It’s only tacd to the axle but I’d really prefer not to remake it again.. what should I be shooting for anti squat wise based off my use? Would moving the frame ends be enough to reach that number. I may be able to move the axle lowers a hair lower depending on when I put it in.

It’ll get lowered some but I won’t know exactly how much till I get a rear axle in it and can jack it up to see true ride height.

Correct on the wishbone.

Click to expand...

The monitor you are using, not the program.

I would probably recommend targeting 30% in the rear. I would recommend moving the upper compared to the lower. If you are moving the frame end, it will change the roll slope less.

Treefrog are you concerned that the front roll center is quite a bit higher then the rear?

It seems like that’s a no go according to busted knuckle

I thought 25% (with 50% front drive bias is perfect for a racer)

06h3 said:

Treefrog are you concerned that the front roll center is quite a bit higher then the rear?

It seems like that’s a no go according to busted knuckle

I thought 25% (with 50% front drive bias is perfect for a racer)

Click to expand...

My memory on roll slopes is usually not great. I'll have to double check which end higher results in understeer.

The reason I suggested slightly higher was the use case. A 4500 that sees mixed use suggests a crawler with desert traits instead of a desert car with crawler traits. If that makes sense.

Treefrog said:

The monitor you are using, not the program.

I would probably recommend targeting 30% in the rear. I would recommend moving the upper compared to the lower. If you are moving the frame end, it will change the roll slope less.

Click to expand...

Would moving the frame end and a lower roll slope be a bad thing? I had plans to run the rear upper link mount with an adjustable mount to be able to move it up or down an inch or so.

Does link length play a role into any of this? I have the option to shorten or length them some but will change the pivot point and my understanding is cause the need for more slip in the driveshaft as the pivot point changes

06h3 said:

Treefrog are you concerned that the front roll center is quite a bit higher then the rear?

It seems like that’s a no go according to busted knuckle

I thought 25% (with 50% front drive bias is perfect for a racer)

Click to expand...

I watched the video from busted knuckle you sent me last night. While some of it I need to go back and rewatch but seems the front roll center can be corrected with a front sway bar which I was already planning on running and one in the rear.