How's my numbers?

[Treefrog]

It’s mainly for rock crawling, AOP. May see the road going to the gas station and such. It’s a tj on tons. I did 2 different locations for upper link on the frame and have both. The unsprung weight is a guesstimate, I can’t tell what the cage is made of, looks store bought.

The second one looks like the better option. Might want to try shortening the upper links, it will probably help with the pinion angles. Raising the panhard up will take the front and body roll slopes towards understeer if you feel the need.

There is some info in here regarding the top view angle of the links for 3 links.

 

[Harleybarnes19]

The second one looks like the better option. Might want to try shortening the upper links, it will probably help with the pinion angles. Raising the panhard up will take the front and body roll slopes towards understeer if you feel the need.

There is some info in here regarding the top view angle of the links for 3 links.

So i took that info and made the uppers 70% of the lowers and it made the anti-dive ideal, according to your link. I also cannot move the axle end lowers in nor the frame end out, just because there's nowhere to go unless I build a sub-chassis. Shortening also made the pinion change a lot better and i think it may be perfect for a double cardon joint at the t-case. moving the panhard up seemed to have little to no effect on the roll slopes (still kinda unsure what that does.)

Thank you for your help, and putting out this resourceful tool! So glad things have been updated since the old V3 version.

 

[Treefrog]

(still kinda unsure what that does.)

Roll slopes influence understeer and oversteer. They aren't the only factor, but they do play a part.

 

[tj-builder]

looking for feedback on my numbers. It's a TJ on 40s, one tons etc. Center of gravity is a total guess and may be completely off. Looking to improve stability. Primarily used for slow rock crawling, not so concerned about high speed. Trailered rig.

 

[Treefrog]

looking for feedback on my numbers. It's a TJ on 40s, one tons etc. Center of gravity is a total guess and may be completely off. Looking to improve stability. Primarily used for slow rock crawling, not so concerned about high speed. Trailered rig.

Guessing you mean side hill stability? What are you running for the spring setup? Coil overs or stock style coil springs? If possible fill in the mounting location info on the shock page. For coilspring setups take the center of the spring buckets.

Front links need more convergence angle. 40 degrees is the recommended minimum.

With CG being a guess, antis aren't going to be accurate. Are you using the general rule of thumbs regarding CG prediction based on the engine? The antis trend of the line will be the same, but the actual values will change.

 

[tj-builder]

Guessing you mean side hill stability? What are you running for the spring setup? Coil overs or stock style coil springs? If possible fill in the mounting location info on the shock page. For coilspring setups take the center of the spring buckets.

Front links need more convergence angle. 40 degrees is the recommended minimum.

With CG being a guess, antis aren't going to be accurate. Are you using the general rule of thumbs regarding CG prediction based on the engine? The antis trend of the line will be the same, but the actual values will change.

Yup - side hill stability. I'm going to be switching to 16" ORI Struts very shortly. Working on getting the mount data inserted.

Makes sense - the CG is a 'wild ass guess' and will work on getting a better one. What will be the primary downside to lack of front triangulation? My understanding is the triangulation helps keep the axle centered and prevents unwanted steering - would it be correct to say that lack of triangulation is less important in the front than the rear in a drag axle?

 

[Treefrog]

Makes sense - the CG is a 'wild ass guess' and will work on getting a better one. What will be the primary downside to lack of front triangulation? My understanding is the triangulation helps keep the axle centered and prevents unwanted steering - would it be correct to say that lack of triangulation is less important in the front than the rear in a drag axle?

Your understanding is correct. Keeping the axle centered is the flip side of keeping the vehicle over the axle. Unwanted steering is affected by all of the geometry, not just triangulation. Not enough and the side forces on the joints are too high.

It would be wrong to say that. It's just as important.

 

[tj-builder]

Your understanding is correct. Keeping the axle centered is the flip side of keeping the vehicle over the axle. Unwanted steering is affected by all of the geometry, not just triangulation. Not enough and the side forces on the joints are too high.

It would be wrong to say that. It's just as important.

The front is a little difficult due to packaging, but it looks like I can push out the front-lowers on the axle side by 2.5" - limited just by the wheel turning into them on full lock, with only needing to re-fabricate the shock/link mount. This brings me to essentially 40 degrees. What do you think of this modification?

Moving the axle side uppers looks like it'll likely have clearance issues on the skids, and anything frame side would be a large undertaking

 

[tj-builder]

Your understanding is correct. Keeping the axle centered is the flip side of keeping the vehicle over the axle. Unwanted steering is affected by all of the geometry, not just triangulation. Not enough and the side forces on the joints are too high.

It would be wrong to say that. It's just as important.

looking at the modification to bring out the lowers axle side on the front, it brings my front roll center lower - which does improve my body roll axis angle, but stability is important to me so i'm unsure if that tradeoff makes sense as long as i'm not breaking my hiem joints and mounts due to lack of triangulation?

 

[Treefrog]

The front is a little difficult due to packaging, but it looks like I can push out the front-lowers on the axle side by 2.5" - limited just by the wheel turning into them on full lock, with only needing to re-fabricate the shock/link mount. This brings me to essentially 40 degrees. What do you think of this modification?

Moving the axle side uppers looks like it'll likely have clearance issues on the skids, and anything frame side would be a large undertaking

Sounds good. Apparently someone on PBB ran the math years ago and the actual minimum is 37.5 or something. I've never been able to track the post down. 40 is much easier to go by.

looking at the modification to bring out the lowers axle side on the front, it brings my front roll center lower - which does improve my body roll axis angle, but stability is important to me so i'm unsure if that tradeoff makes sense as long as i'm not breaking my hiem joints and mounts due to lack of triangulation?

Lower roll center will result in more body roll. There are some advantages to a low RC but most of them have are speed related. As for slow advantages, more warning before it rolls and the axle swings side to side less during articulation.

How wide you can mount your springs will play a bigger roll in keeping it stable.

I don't know if they will work in your application, but have you considered bent lowers or uppers?

 

[tj-builder]

Sounds good. Apparently someone on PBB ran the math years ago and the actual minimum is 37.5 or something. I've never been able to track the post down. 40 is much easier to go by.

Lower roll center will result in more body roll. There are some advantages to a low RC but most of them have are speed related. As for slow advantages, more warning before it rolls and the axle swings side to side less during articulation.

it sounds like your suggesting even if stability is something i'm seeking, that I should go for more triangulation even if I have to lower my roll center more? Is below the '37.5' or so a 'absolutely do not do no matter what' type of thing? I believe in the history of the rig it's never blown a heim joint (which are pretty beefy)

How wide you can mount your springs will play a bigger roll in keeping it stable.

Luckily I Have full widths and are mounted in a way that i think will be favorable to stability. Currently I have FOAs, one of which is blown and leaking oil (driver side rear). I added some pictures on rocker knocker, Pritchett canyon which demonstrate the lean.

I am working on fabricated some new rear upper strut mounts for my ORIs (since they don't clear the roll cage - the old coilovers were more narrow up top). Would pushing the upper mount more inwards be beneficial for stability? Currently there is roughly a 4" horizontal offset from top mount to bottom mount, and I need to bring it to a minimum of around 4.5". Should I go bigger and push it even more inwards, around the 6" range? I already have big holes in my tub and have lots of room to change where the upper strut mounts go.

 

[Treefrog]

it sounds like your suggesting even if stability is something i'm seeking, that I should go for more triangulation even if I have to lower my roll center more? Is below the '37.5' or so a 'absolutely do not do no matter what' type of thing? I believe in the history of the rig it's never blown a heim joint (which are pretty beefy)


Luckily I Have full widths and are mounted in a way that i think will be favorable to stability. Currently I have FOAs, one of which is blown and leaking oil (driver side rear). I added some pictures on rocker knocker, Pritchett canyon which demonstrate the lean.

I am working on fabricated some new rear upper strut mounts for my ORIs (since they don't clear the roll cage - the old coilovers were more narrow up top). Would pushing the upper mount more inwards be beneficial for stability? Currently there is roughly a 4" horizontal offset from top mount to bottom mount, and I need to bring it to a minimum of around 4.5". Should I go bigger and push it even more inwards, around the 6" range? I already have big holes in my tub and have lots of room to change where the upper strut mounts go.

40 is considered the absolute do not go past. Past that point the links begin to not hold the axle under the vehicle. Yes, having the needed triangulation is more important than keeping the roll center high.

The other option is go to a 3 link with a track bar.

Generally speaking the wider shock mounts should provide more roll resistance.

If the rear always flexes more than the front as much as your front end image shows, a light sway bar to stiffen the rear end may be the solution.

 

[tj-builder]

I think those images have a lot going on - since each tire is on a different ledge and the camera is pointed at artistic angles. I've included a simpler image that shows how the rear behaves when on a flat ground with a single tire raised. In the image with the flex being shown, the rear is still has a bit of travel before it maxes out the 16s. With the dovetail and back half, it is able to fully articulate the full 16s in the rear. I also included a max flex on just the rear.

It does seem to like to articulate more in the rear, but I'm not a good judge on whether this is 'way more than you want' or 'just a little more' or totally normal. But also this picture is taken with a under-charged rear-driver coilover, which I think may be exaggerating the effect. I plan on testing some more once I have the ORIs in and see how it behaves.

I've included an image of the rear shock mount, it does look like to me I could move it out another inch or so. The axle is full width, so it is quite wide already. Do you think it would be worth moving out an inch?

Lastly on sway bar - I don't believe I can package one in without doing something quite extreme. You'll see frame is frenched - at full droop the struts/coilovers will come very close to the frame. Since they are also mounted wide (and potentially moving even wider), I can't really mount the sway bar outside of the struts/coilovers either. That would leave me with needing to have the swaybar mounted behind the rear axle instead, though I keep hearing people suggest against that? Of course - I will be doing things one step at a time and re-evaluating how it drives at each step, but it's something I am thinking about now so I can have a clear path on potential futures for this rig.

 

[Treefrog]

I think those images have a lot going on - since each tire is on a different ledge and the camera is pointed at artistic angles. I've included a simpler image that shows how the rear behaves when on a flat ground with a single tire raised. In the image with the flex being shown, the rear is still has a bit of travel before it maxes out the 16s. With the dovetail and back half, it is able to fully articulate the full 16s in the rear. I also included a max flex on just the rear.

It does seem to like to articulate more in the rear, but I'm not a good judge on whether this is 'way more than you want' or 'just a little more' or totally normal. But also this picture is taken with a under-charged rear-driver coilover, which I think may be exaggerating the effect. I plan on testing some more once I have the ORIs in and see how it behaves.

I've included an image of the rear shock mount, it does look like to me I could move it out another inch or so. The axle is full width, so it is quite wide already. Do you think it would be worth moving out an inch?

Lastly on sway bar - I don't believe I can package one in without doing something quite extreme. You'll see frame is frenched - at full droop the struts/coilovers will come very close to the frame. Since they are also mounted wide (and potentially moving even wider), I can't really mount the sway bar outside of the struts/coilovers either. That would leave me with needing to have the swaybar mounted behind the rear axle instead, though I keep hearing people suggest against that? Of course - I will be doing things one step at a time and re-evaluating how it drives at each step, but it's something I am thinking about now so I can have a clear path on potential futures for this rig.

It probably isn't worth moving out an inch. At some point you begin to run into tire clearance issues when articulating.

One of the best ways to check which ends moves more and how much more is to drive in a circle, preferably on dirt in 4h, at a constant speed and get someone to take a picture of the front and the rear. Its only way more than wanted when one end is all the way flexed out and the other has only begun to move.

There are reasons to not mount a sway bar behind the axle, but plenty of people do it.

 

[OffroadAddict]

First off Treefrog, you are a legend! Thank you for reworking this and giving us more information than we can shake a stick at. I had a thought for a potential bit of info that would be an amazing addition... What about steering angle or measuring it as a dimension from lock to lock that moves the tire in the diagram so we can see how close we are to rubbing on the links?

I would love a bit of feedback on these options I have been playing around with, first one is 75%ish upper to lower (actual link length not in side view) and the other is approx equal.

Tube frame buggy built to sit inside a stretched CJ4A body with a slight dovetailed rear, 38.5" Mud Treps will be 90% mud and slow stuff and 10% "Fast" (likely will very rarely see over 65mph). 12" Coilovers front, 14" air shocks rear, hydro steer etc.

Apologies for the lack of freedom units!

 

[Treefrog]

First off Treefrog, you are a legend! Thank you for reworking this and giving us more information than we can shake a stick at. I had a thought for a potential bit of info that would be an amazing addition... What about steering angle or measuring it as a dimension from lock to lock that moves the tire in the diagram so we can see how close we are to rubbing on the links?

I've considered adding that feature and its definitely something I want to do. The logic behind the math is pretty easy. But there are some things keeping me from doing it at the moment.

• Version 7 is in the works and the less new features added in the update the less troubleshooting and the quicker it gets finished.
• There are a ton of variables besides turn angle. Backspacing, WMS to pivot distance, caster, possibly camber, etc. Not show stoppers but they complicate things.
• If its gonna be modeled, its gonna be in 3d, and it needs to be able to do it at any travel point.
• Its hard enough to keep track of 2.5d math in Excel, I don't have the ambition to try 3d to the extent needed for this in Excel.

I would love a bit of feedback on these options I have been playing around with, first one is 75%ish upper to lower (actual link length not in side view) and the other is approx equal.

Tube frame buggy built to sit inside a stretched CJ4A body with a slight dovetailed rear, 38.5" Mud Treps will be 90% mud and slow stuff and 10% "Fast" (likely will very rarely see over 65mph). 12" Coilovers front, 14" air shocks rear, hydro steer etc.

Both look good. The one with the 75% uppers is probably a little better. Probably want to narrow the front up some, looks like tires will hit. You may want to try to get it so that the rear stays below 50% AS through the travel range. Other than that, check the pitch page to see what things do when both axles are moving.

Apologies for the lack of freedom units!

Cool to see metric being used. Does everything look reasonable? I didn't do much if any testing and checking on that side of things.

 

[OffroadAddict]

I've considered adding that feature and its definitely something I want to do. The logic behind the math is pretty easy. But there are some things keeping me from doing it at the moment.

• Version 7 is in the works and the less new features added in the update the less troubleshooting and the quicker it gets finished.
• There are a ton of variables besides turn angle. Backspacing, WMS to pivot distance, caster, possibly camber, etc. Not show stoppers but they complicate things.
• If its gonna be modeled, its gonna be in 3d, and it needs to be able to do it at any travel point.
• Its hard enough to keep track of 2.5d math in Excel, I don't have the ambition to try 3d to the extent needed for this in Excel.

Both look good. The one with the 75% uppers is probably a little better. Probably want to narrow the front up some, looks like tires will hit. You may want to try to get it so that the rear stays below 50% AS through the travel range. Other than that, check the pitch page to see what things do when both axles are moving.

Cool to see metric being used. Does everything look reasonable? I didn't do much if any testing and checking on that side of things.

Thanks for the info, I knew you would call me on the front links haha. I noticed it as I was posting, shouldn't stay up til 2am punching numbers it's not good for accuracy. I went way down the rabbit hole in all the threads old and new to refresh and relearn some ideas, found some wicked info and playing in the calc in real-time while learning was awesome.

Everything worked as it should, the only complaint, if I'm being a fussy prick about a phenomenal free tool, is changing from Metric to Imperial doesn't change the values ie 2" converts to 2mm rather than 50.8mm. I went to convert it back before posting to make it easier for you but no deal.

Also, just a grain of salt bit of feedback and it's likely cos I was dropped at birth but those graphs make my head hurt. I think it's because I am running numbers in my head then a picture throws my thought train off. I can make sense of them and I think you have done an insane job with this but when I'm playing with numbers I find it easier to understand numbers (like the slightly older versions).

 

[Treefrog]

Thanks for the info, I knew you would call me on the front links haha. I noticed it as I was posting, shouldn't stay up til 2am punching numbers it's not good for accuracy. I went way down the rabbit hole in all the threads old and new to refresh and relearn some ideas, found some wicked info and playing in the calc in real-time while learning was awesome.

Everything worked as it should, the only complaint, if I'm being a fussy prick about a phenomenal free tool, is changing from Metric to Imperial doesn't change the values ie 2" converts to 2mm rather than 50.8mm. I went to convert it back before posting to make it easier for you but no deal.

Also, just a grain of salt bit of feedback and it's likely cos I was dropped at birth but those graphs make my head hurt. I think it's because I am running numbers in my head then a picture throws my thought train off. I can make sense of them and I think you have done an insane job with this but when I'm playing with numbers I find it easier to understand numbers (like the slightly older versions).

2 am number punching got me in trouble a few times while making it.

If I could have it auto change the values I would have. I spent a fair bit of time looking seeing if it was reasonably possible. Another one of the limitations of Excel.

Just look at the numbers on the plots. Highlight travel is probably your friend here. The numbers had their advantage, but I found that they hid what was actually going on, and with the increase in data points it wasn't feasible to stick with them. And with the next version having the ability to do way way more data points, they won't be returning. That said, any suggestions for improving it like adding a second highlighted travel, I am all ears.

 

[OffroadAddict]

2 am number punching got me in trouble a few times while making it.

If I could have it auto change the values I would have. I spent a fair bit of time looking seeing if it was reasonably possible. Another one of the limitations of Excel.

Just look at the numbers on the plots. Highlight travel is probably your friend here. The numbers had their advantage, but I found that they hid what was actually going on, and with the increase in data points it wasn't feasible to stick with them. And with the next version having the ability to do way way more data points, they won't be returning. That said, any suggestions for improving it like adding a second highlighted travel, I am all ears.

Surely CTRL+A =VALUEx25.4 will do the job for you What about having Imperial / Metric on split worksheets that work off a times or divide formula? Probably a waste of time considering most will be working in their preferred measurements though.

Reading numbers AND looking at pictures... way above my pay grade!

To be honest highlight travel was one of the things that I struggled with - a keynote here would be valuable. My initial thought process on the Highlighted travel was that this was the value of casual driving ie ride height travel +/- 1" would make up the 2" of travel that I want to see. I still don't think I actually wrapped my head around it but I haven't played with it to see what values it changes yet. I don't mind being the idiot that doesn't understand for the sake of learning... what does it do and how do we utilize it best?

 

[Treefrog]

Surely CTRL+A =VALUEx25.4 will do the job for you What about having Imperial / Metric on split worksheets that work off a times or divide formula? Probably a waste of time considering most will be working in their preferred measurements though.

Reading numbers AND looking at pictures... way above my pay grade!

To be honest highlight travel was one of the things that I struggled with - a keynote here would be valuable. My initial thought process on the Highlighted travel was that this was the value of casual driving ie ride height travel +/- 1" would make up the 2" of travel that I want to see. I still don't think I actually wrapped my head around it but I haven't played with it to see what values it changes yet. I don't mind being the idiot that doesn't understand for the sake of learning... what does it do and how do we utilize it best?

Excel either has a formula in a cell or doesn't. No good way to have it decide to have a formula or an input based on another cell. Its all moot at this point. Its something that is easy to do in V7.

Highlight travel puts a probe at a specific point of travel. All it does is move the odd colored marker on the plots. It's purpose is so that you can say I wonder what the values at X travel is. I'll probably change its name to make it clearer going forward.

 

[OffroadAddict]

Ahh right, that makes sense! Having highlight travel explained and setting the value at 0 made things a lot easier to understand, thanks!

Have punched a few more numbers and got them slightly better (I think)

 

[Treefrog]

Ahh right, that makes sense! Having highlight travel explained and setting the value at 0 made things a lot easier to understand, thanks!

Have punched a few more numbers and got them slightly better (I think)

Looks good. Only thing I can see is the front might not be narrow enough. And maybe lower the front roll center 20mm so that the roll slope is always negative in pitch. Moving the links in will lower it.

 

[OffroadAddict]

Looks good. Only thing I can see is the front might not be narrow enough. And maybe lower the front roll center 20mm so that the roll slope is always negative in pitch. Moving the links in will lower it.

Awesome man, thank you so much for the input. Always good to get some eyeballs on it, much appreciated!

Luckily I have the axle on roller wheels outside so managed to double check some measurements and narrow the front end up as much as possible, and dropped 20mm from the front roll centre. Still in the 40* convergence angle (just - 43.7*)

 

[Kubi]

Treefrog. Mind shining your wisdom on yet another build? This is a jeep LJ that i'm shooting for an ULTRA4/Rock Race setup. I had been doing it with the old 1 side calculator. But stumbled upon yours and am redesigning it yet again. Tear it apart and let me know your opinions. I'm looking forward to learning. Also, thank you for being such a great source of help and knowledge.

 

[Treefrog]

Treefrog. Mind shining your wisdom on yet another build? This is a jeep LJ that i'm shooting for an ULTRA4/Rock Race setup. I had been doing it with the old 1 side calculator. But stumbled upon yours and am redesigning it yet again. Tear it apart and let me know your opinions. I'm looking forward to learning. Also, thank you for being such a great source of help and knowledge.

Looks pretty good overall. Which class(es) is this being built for? Guessing 4500? Watch out for tire size. Design to the class even if its sub optimal for trail riding. If it is 4500, you can probably get another .5 inches up and down travel pretty easily by angling the shocks. And even more with some other tricks.

Belly height may be a little low. Probably going to end up around 16.5" of clearance below the link mounts. The vehicle roll slopes are all negative (oversteer) . It may be better to have them all positive (understeer).

It may be beneficial to have the rear antis increase with up travel. It also may be a good idea to increase the convergence angle of the front to help with side forces.

 

[Kubi]

I wish, but not to compete, just for fun, so im not constrained by the class rules. im going to trail it as well. i just know im going to start going faster and pushing it sooner than i want. in the future ill build something from the ground up with everything i learn here. What tricks are ya talking about with the angles, etc? ive been teaching myself over the last year. So you're the first person to give me great pointers.

Unfortunately the front axle is so narrow that's why im getting such bad convergence numbers. I could move the lowers out a little and sacrifice some steering angle. maybe pull the axle back a little too.

So im having trouble flipping the rear antisquat curve and the vehicle roll slopes. Any more tricks there. Thanks for doing what you do brother.

 

[Treefrog]

I wish, but not to compete, just for fun, so im not constrained by the class rules. im going to trail it as well.

You may want to move the lower frame points up then. A belly that low may make the 40s not feel like 40s.

i just know im going to start going faster and pushing it sooner than i want. in the future ill build something from the ground up with everything i learn here. What tricks are ya talking about with the angles, etc? ive been teaching myself over the last year. So you're the first person to give me great pointers.

If you lean the shocks in and/or forward you can increase wheel travel for a given shock travel. Another trick is to mount the shock on in front of the rear axle. With larger pinion rotation in the correct directions you can get a bit of extra travel out of it. Downside to getting more travel out of it is that you reduce the effectiveness of the shock. That means more damping and spring needed.

Unfortunately the front axle is so narrow that's why im getting such bad convergence numbers. I could move the lowers out a little and sacrifice some steering angle. maybe pull the axle back a little too.

Can you move the lower frame in at all?

So im having trouble flipping the rear antisquat curve and the vehicle roll slopes. Any more tricks there. Thanks for doing what you do brother.

My guess is to try shortening the uppers.

 

[bscottroberts]

TJ on Tons and 40s. I have an issue where if I am going around a sweeping turn (like an highway exit off ramp) and hit a bump in the turn the jeep darts a little to the side. I think it is rear steer. It use to be worse -added a rear sway bar and that made it better. I would like to improve it some more. What should I focus on? Both the front and rear upper frame mounts have adjustability up and down- so that is easiest to try first. Any input is appreciated.

 

[Treefrog]

TJ on Tons and 40s. I have an issue where if I am going around a sweeping turn (like an highway exit off ramp) and hit a bump in the turn the jeep darts a little to the side. I think it is rear steer. It use to be worse -added a rear sway bar and that made it better. I would like to improve it some more. What should I focus on? Both the front and rear upper frame mounts have adjustability up and down- so that is easiest to try first. Any input is appreciated.

A picture of the roll slope and roll center plots would help. And a picture of the front of the vehicle showing the panhard bar and steering linkages would help.

My guess is that it is not suspension geometry but steering geometry. The darting when it hits a bump comes across as bump steer. Does it dart when one wheel hits a bump when not turning?

 

[bscottroberts]

Treefrog- The trac bar and draglink are both 32.5" and within 1 degree of being parallel to each other (used a string between the mounting bolts for the tracbar, since it has a bend in it.)

Here is the Roll Slope and Roll Center that you requested. It doesn't swerve bad- fine for me. I just am trying to make it a little better, so my wife feels more comfortable driving it.
Appreciate you taking a look.