How's my numbers?

[Treefrog]

This leads to a question I've had, but never asked. I feel like the consensus is to get the AD down in the 30-50% range and go toward the lower end of that if you're anticipating faster dez stuff. Are those numbers based on a drive bias of 0% or 50%? 50% drive bias halves the AD so I figured I was good. I'll be doing east coast trail wheeling with some limited street time.

The 30-50% range for dessert stuff and the 50-80% range that crawlers tend towards were based on 100% rear drive. I can never remember if the calc is set up with 0 or 1 as rwd.

 

[j.mcconnell]

The 30-50% range for dessert stuff and the 50-80% range that crawlers tend towards were based on 100% rear drive. I can never remember if the calc is set up with 0 or 1 as rwd.

Ahh. I was thinking that was in 4wd so I had it at 80 in RWD. Thanks

 

[Team_Jake]

This is my first time building something like this so I want to make sure I'm not too far off the mark.
'99 4Runner, 3/4 linked, Superduty Axles, 40s, will be driven on the street/highway.
Anything look sketchy?

Thank you!

 

[Treefrog]

This is my first time building something like this so I want to make sure I'm not too far off the mark.
'99 4Runner, 3/4 linked, Superduty Axles, 40s, will be driven on the street/highway.
Anything look sketchy?

Thank you!

Looks pretty good. Assuming the panhard is parallel to steering, it may be worth some time trying to get them flatter. But it's no worse than something like a lifted Jeep or truck.

 

[Team_Jake]

Looks pretty good. Assuming the panhard is parallel to steering, it may be worth some time trying to get them flatter. But it's no worse than something like a lifted Jeep or truck.

Currently the drag link follows the panhard very close, I'll look into trying to get them a little flatter, thank you!

 

['84 Bronco II]

I might as well post up some numbers from the buggy I am building. The weights and CG location are educated guesses since it is not built yet, but I think they should be pretty close based on similar builds.

The link mounting locations are based on chassis mounts I bought from the builder and his notes on how to set up the link mounting locations on both the axles and chassis. The rear chassis-side mounts and the front chassis-side lowers are already welded in, but the front chassis-side uppers and axle-side mounting locations front and rear could be tweaked if needed.
I am not really concerned about anything in particular since I know these chassis setup to the builder's specifications perform very well, but I figured I would post it up in case anyone sees something concerning or something that could benefit from some slight tweaking. This is primarily a crawler that will see really steep verticals, but it will also be driven quite a bit at speed through open desert.

That said, the caster change in the front seems a bit much for higher speeds (drive shafts will be almost flat, so not too concerned about angles), and the anti dive seems bad for going down steep descents since the more the suspension compresses, the less resistance it has to compressing further under braking. However, the anti lift curve seems to sloped correctly for the chassis to want to hunker down when climbing, and I am not sure how inter-related that is with the anti-dive geometry. I am far from an expert though, so these two things may be complete non-issue.

 

[Bebop]

I am not really concerned about anything in particular since I know these chassis setup to the builder's specifications perform very well, but I figured I would post it up in case anyone sees something concerning or something that could benefit from some slight tweaking. This is primarily a crawler that will see really steep verticals, but it will also be driven quite a bit at speed through open desert.

Don't overthink the caster change. It is rare that you will turn sharp at speed.
Driveshaft plunge on the other hand is a real problem at speed. Make sure you account for that.

In my personal experience, anything setup to go fast will go slow well. Not the other way around.

If these chassies are know to work well the way the builder is setting them up, I'd tend to follow that and not overthink it. Experience > numbers.

 

['84 Bronco II]

Don't overthink the caster change. It is rare that you will turn sharp at speed.
Driveshaft plunge on the other hand is a real problem at speed. Make sure you account for that.

In my personal experience, anything setup to go fast will go slow well. Not the other way around.

If these chassies are know to work well the way the builder is setting them up, I'd tend to follow that and not overthink it. Experience > numbers.

I agree, and I need to punch in the yoke locations for the transfer case once I settle on a final location to makes sure all the driveshafts stuff is kosher.

I starting putting all this into the calculator primarily to satisfy my own curiosity on the numbers for a "good" setup, and figured I might as well share. I am also interested to hear some opinions from people who are better versed in link suspension design than I am, and hopefully learn some more. I am not really planning on making any changes, but I am open to discussion.

 

[Treefrog]

I might as well post up some numbers from the buggy I am building. The weights and CG location are educated guesses since it is not built yet, but I think they should be pretty close based on similar builds.

The link mounting locations are based on chassis mounts I bought from the builder and his notes on how to set up the link mounting locations on both the axles and chassis. The rear chassis-side mounts and the front chassis-side lowers are already welded in, but the front chassis-side uppers and axle-side mounting locations front and rear could be tweaked if needed.
I am not really concerned about anything in particular since I know these chassis setup to the builder's specifications perform very well, but I figured I would post it up in case anyone sees something concerning or something that could benefit from some slight tweaking. This is primarily a crawler that will see really steep verticals, but it will also be driven quite a bit at speed through open desert.

That said, the caster change in the front seems a bit much for higher speeds (drive shafts will be almost flat, so not too concerned about angles), and the anti dive seems bad for going down steep descents since the more the suspension compresses, the less resistance it has to compressing further under braking. However, the anti lift curve seems to sloped correctly for the chassis to want to hunker down when climbing, and I am not sure how inter-related that is with the anti-dive geometry. I am far from an expert though, so these two things may be complete non-issue.

It is nice to see data from known good designs.

The antidive is not nearly as bad as it looks. When on a hill, the lower end will be close to ride height, assuming fairly even weight split. On top of that the drive/brake bias shifts to almost entirely on the lower end. So on a down hill, you will be looking at around 80% AD. When hard on the brakes on flat ground, the front will soften instead of stiffen too.

As mentioned by Bebop, don't overthink caster. It gets better with up travel (higher loading) and worse with down travel (lower loading). Also, give the pitch page a check. You may find that caster relative to the ground doesn't change much. You will have to look at the relative positions of the axle link ends. It doesn't report the effective caster change value.

I agree, and I need to punch in the yoke locations for the transfer case once I settle on a final location to makes sure all the driveshafts stuff is kosher.

I starting putting all this into the calculator primarily to satisfy my own curiosity on the numbers for a "good" setup, and figured I might as well share. I am also interested to hear some opinions from people who are better versed in link suspension design than I am, and hopefully learn some more. I am not really planning on making any changes, but I am open to discussion.

Kind of like with CG, you can estimate the T-case stuff and get a rough idea of how good/bad it is. But just from the axle pinion change and flat driveshafts, it looks like you should be fine. Standard crawler 4 links have less driveshaft movement than radius arms or leaf springs do.

Please keep us updated on it. It would be nice to have more eyes on the other parts of the calc and the discussions that will follow.

 

[YeeP]

Im finally to the point on my chassis/steering setup that I feel like I can put down numbers that I can achieve. At this point I am fairly happy with the numbers I have except the pinion change over suspension travel. Purpose of the rig is technical crawling, no road use. The only numbers I am working on right now are for the front end, but obviously I will be taking what I can do to the front and attempting to "balance" it with the read when I get to that part of the build. The last time we talked, I was given the suggestion to make the lowers more "parallel" (assuming that meant with the ground), and to increase the convergence angle on the uppers.

As far as flexibility in adjustment, the places I probably can't change are:
Lower Axle: Y
Lower Frame: Z, (if Y needs to go down, X will need to increase)

The uppers will take some chassis changes especially on the frame side changes (obviously), but I am willing to do that if I can get these numbers 'better'.

EDIT: Also my brake bias numbers have not been touched, Im no where near being able to get an idea of how my brakes are working.

Thanks!

 

[Treefrog]

Im finally to the point on my chassis/steering setup that I feel like I can put down numbers that I can achieve. At this point I am fairly happy with the numbers I have except the pinion change over suspension travel. Purpose of the rig is technical crawling, no road use. The only numbers I am working on right now are for the front end, but obviously I will be taking what I can do to the front and attempting to "balance" it with the read when I get to that part of the build. The last time we talked, I was given the suggestion to make the lowers more "parallel" (assuming that meant with the ground), and to increase the convergence angle on the uppers.

As far as flexibility in adjustment, the places I probably can't change are:
Lower Axle: Y
Lower Frame: Z, (if Y needs to go down, X will need to increase)

The uppers will take some chassis changes especially on the frame side changes (obviously), but I am willing to do that if I can get these numbers 'better'.

EDIT: Also my brake bias numbers have not been touched, Im no where near being able to get an idea of how my brakes are working.




Thanks!

For getting a higher roll center more parallel had been relative to each other not the ground. But if you are locked into your lower axle Y, that is not much of an option. From looking at you current numbers, increasing upper axle Y will help raise the roll center. But it will move more through travel if you do.

Pinion change is in your favor here for a technical crawler.

If you are able to get the antis down so that front AL maxes out below 50% with the current biases, it will be in your favor. Try increasing lower axle Z to make the link flatter.

I HIGHLY recommend designing the front and rear at the same time. That way you do not get into a position where you cannot get the rear to work well with the front.

 

[YeeP]

Designing them together is a good idea. My current issue is funds. I can design and mock the front right now. To do both I will need to save up a bit.

 

[Treefrog]

Designing them together is a good idea. My current issue is funds. I can design and mock the front right now. To do both I will need to save up a bit.

Even if you make build one end at a time, it still helps to design both at the same time. Even if you have to move some of the rear points a little when you go to build it, having a rough plan is better than nothing.

 

[YeeP]

Even if you make build one end at a time, it still helps to design both at the same time. Even if you have to move some of the rear points a little when you go to build it, having a rough plan is better than nothing.

Alright Ill start mocking it up.

Also, I see that the pinion change is actually good for what I need while cycling. I am just trying to not loose so much caster while flexing downward. I guess I see any large caster changes in the suspension cycling as something that would make the steering performance erratic.

 

[Treefrog]

Alright Ill start mocking it up.

Also, I see that the pinion change is actually good for what I need while cycling. I am just trying to not loose so much caster while flexing downward. I guess I see any large caster changes in the suspension cycling as something that would make the steering performance erratic.

Caster change is less of an issue on a crawler since the speeds are lower and steering is hydraulic. And the point at which it gets iffy is when there is little force on the tire.

 

[YeeP]

Even if you make build one end at a time, it still helps to design both at the same time. Even if you have to move some of the rear points a little when you go to build it, having a rough plan is better than nothing.

I cut down my rear housing and mounted the Inner Cs and knuckles based on your input. I don't see any reason that I can't damn near replicate the front end on the back. I have a lot more flexibility and room in the back. The chassis does have some lower mounts already welded to it, which I might put into the file just to see what it would look like. Worst case though, I can remove them and start fresh to make something that is nearly a mirror image of the front.

 

[Treefrog]

I cut down my rear housing and mounted the Inner Cs and knuckles based on your input. I don't see any reason that I can't damn near replicate the front end on the back. I have a lot more flexibility and room in the back. The chassis does have some lower mounts already welded to it, which I might put into the file just to see what it would look like. Worst case though, I can remove them and start fresh to make something that is nearly a mirror image of the front.

The biggest reasons against an exact replica for the rear are amount of travel, pinion angle, and roll center. Pinion angle is not a issue here since crawler. Roll center is often at a different height depending on if understeer or oversteer is desired.

 

[YeeP]

The biggest reasons against an exact replica for the rear are amount of travel, pinion angle, and roll center. Pinion angle is not a issue here since crawler. Roll center is often at a different height depending on if understeer or oversteer is desired.

• I am attempting to run a 6" up, 10" down travel both front and rear.
• pinion angle I am starting at 0 degrees for both front and rear as I am not running a CV driveshaft, and have high pinion diffs in both (front driveshaft is nearly parallel to the ground at RH, rear is approximately 5 degrees upward)
• I can tweak the roll center if you think it should be higher or lower.

For a desired understeer vs oversteer, I guess I need to read up. I am not sure what my preference would be for front or rear axle. I have been trying to stay as close to 0 in either direction whenever possible.

 

[Treefrog]

The driveshaft tab will help with angles. The one you are looking at is just change from ride.

You often want the front higher or lower than the rear. I can never remember which direction is oversteer and which is understeer. The 4 link thread linked in post 1 should have it.

Near 0 is normally the target for front, rear, and vehicle roll axis.. For a dedicated crawler, I tend to recommend oversteer for the responsiveness. Understeer helps to keep faster vehicles under control.

 

[YeeP]

You often want the front higher or lower than the rear. I can never remember which direction is oversteer and which is understeer. The 4 link thread linked in post 1 should have it.

So I searched in the bible and 4-link calc threads since I wasnt sure what you were referring to.
In the Bible one, I just did a search for the string 'understeer'

• December's Bible Build: Linked Suspensions
• December's Bible Build: Linked Suspensions
• December's Bible Build: Linked Suspensions

'oversteer' actually produces less results.
The 4 link calculator thread had no hits on 'understeer'.

Based on those three posts, Im guessing maybe you are remembering the model you created on a 3 link? Does looking at that jog your brain on what you were thinking?

A simple Google search yielded me these results:
Note: Most of the Squat percentages in these older threads are from the old version of the calculator and use a 'bias' of 1. Im not sure I quite understand that but anyone that has read the bible on this forum will know that these AS #s are not apples to apples with what you are looking at in the updated calculator.

oversteer vs understeer

www.pirate4x4.com

Great post from Triaged here: help understanding A frame geoomertry

It changes roll steer aka flex steer. In the case of roll oversteer you will turn the wheel and enter a corner. The body will roll out of the corner, the body roll will skew the rear axle pointing the rear tires to the outside of the turn. In other words the more body roll the more it will turn so you will have to reduce your steering input in order to keep the truck on the road. There is also compliance steer which with a triangulated 4-link is also in the oversteer direction. I.e. any deflection of the links, bushings, or mounts will cause the vehicle to turn sharper. Understeer is considered to be a more benign reaction which is why I suggested you triangulate the lower links. IMO you should have anywhere from 0-5° roll understeer which will work well on the street and crawling but won't be so good at drifting around corners. GM cars with triangulated 4-links had about 10° of roll understeer built into them most likely to balance out compliance oversteer from the soft bushings. Suspensions with a Panhard bar behind the axle have compliance understeer.

Interesting take by Erik B: tacoma/4runner suspension calculation census

OK, I FINALLY figured out why my pass. side ball joints kept getting loose!

My steering arm was contacting the inner-C just before full lock left, and that would pry on the BJ and make it loose. Part of it is because I'm set up to steer so sharp, and part of it is because the Parts Mike arm has more meat to it. My old arm on the last rig never contacted.

So I did some minor grinding on the arm, replaced the ball joints on that side again, and the rig drives MUCH better!
Rig doesn't wander like it used to (go figure :p), and changes in caster are more noticeable.

At 9* caster the steering response is kind of slow/poor, but it drives nice on the freeway and the oversteer is slower and more predictable.

At 2* caster the steering response is very quick/tight, but the rig is twichy, probably because of the oversteer. It would probably suck w/o the swaybars with this low of caster, as Booger seems to have found out with his rig.

For now I've settled on 4* and the rig is fun to drive again.


Summary/hindsight-
After nearly a year of driving this thing and tinkering with it, here's what I would do if I were starting over (or what I would recommend for people starting a build and looking for input for good handling):

• 
  Bottom line is I'd try to get get slight UNDERsteer from the suspension, especially up front. You can do this by mounting the panhard high and triangulating the lowers (play with it in the link calculator).

• I would triangulate both front and rear lower links and mount the frame ends a little lower, sacrificing a little more ground clearance at the belly in the center (think boatsided rig or comp buggy with low center). This helps improve/reduce the oversteer by making the lower link intersection lower and also reduces anti-squat/dive.

• I'd mount the lower rear link axle ends above axle centerline. This would improve ground clearance at that end of the links and also reduce anti-squat/dive. The front doesn't matter as much for this, IMHO.

• I'd mount the panhard higher up front by either cutting the frame or using a bent link, or both. Part of helping reduce the oversteer.

• I'd use longer shocks. I could have easily fit 16's up front. I don't think I could fit more than the 14's I have in the back though w/o cutting.

All of this is primarily for street and/or high speed off road handling (desert/KOH stuff). I don't think it would make much difference crawling.
I may go back and change some of this stuff, but we'll see how motivated I am next winter...

I've seen some of the KOH guys comment about how getting the rig to handle the high speed stuff was the most challenging and made the biggest difference, but the rigs still worked well in the rocks. (a lot of those comments were about shock tuning, but I think in general it all applies).

My $.02 and then some...

Treefrog: I'll keep searching, but the main consensus I have seen is: slightly more understeer in the front than rear, both relatively low values, will help in higher speed. Also it is easy to mix the two different 'steer' terms (oversteer vs roll oversteer) in my simple brain. It also makes me wonder if others are mixing them up. For instance, I know Traiged knows his stuff, but I swear in his 'IMO' sentence he is actually referring to understeer, not roll understeer. anyway.... I will keep searching and post here in an effort to help with future questions like mine.

 

[Treefrog]

So I searched in the bible and 4-link calc threads since I wasnt sure what you were referring to.

Bible. Sorry, should have been more clear.

In the Bible one, I just did a search for the string 'understeer'

• December's Bible Build: Linked Suspensions
• December's Bible Build: Linked Suspensions
• December's Bible Build: Linked Suspensions

'oversteer' actually produces less results.
The 4 link calculator thread had no hits on 'understeer'.

Based on those three posts, Im guessing maybe you are remembering the model you created on a 3 link? Does looking at that jog your brain on what you were thinking?

From the first of the 3 links:

Rear Roll Axis: Slopes down towards front - understeer

Front Roll Axis: Slopes down towards rear - understeer

Vehicle Roll Axis: Slopes down towards front- oversteer

Lower front roll center results in the vehicle roll axis having roll oversteer. I have a hard time remembering if a lower front roll center is oversteer or understeer.

A simple Google search yielded me these results:
Note: Most of the Squat percentages in these older threads are from the old version of the calculator and use a 'bias' of 1. Im not sure I quite understand that but anyone that has read the bible on this forum will know that these AS #s are not apples to apples with what you are looking at in the updated calculator.

oversteer vs understeer

www.pirate4x4.com

Basically, the old calc did math for 2wd. With all of the acceleration or deceleration being done by the end that was in the calculator. The newer ones can do anything from all rear, all front, and anything in between. This does not affect OS/US.

Great post from Triaged here: help understanding A frame geoomertry


Interesting take by Erik B: tacoma/4runner suspension calculation census


Treefrog: I'll keep searching, but the main consensus I have seen is: slightly more understeer in the front than rear, both relatively low values, will help in higher speed.

Mostly correct. Geometric US is preferred for all 3 roll axis: front, rear, vehicle. It does not make much difference if the front has more than the rear, as the front and rear roll centers, not their roll axis, control the vehicle roll axis's slope.

Two important parts for US in a corner

1. Roll causes the outer tires move towards the back of the vehicle compared to the respective inner tire.
2. The front roll center is higher than the rear's

US causes the vehicle to tend to continue in the same heading as the body rolls instead of turning in more. This is done because it's safer for the average driver going to the mall. It is not a requirement.

Easy way to check a car is to go drive in a circle and hold the steering wheel in one place. If the circle gets bigger as you increase speed, it has US. Getting smaller means OS.

Also it is easy to mix the two different 'steer' terms (oversteer vs roll oversteer) in my simple brain. It also makes me wonder if others are mixing them up. For instance, I know Traiged knows his stuff, but I swear in his 'IMO' sentence he is actually referring to understeer, not roll understeer. anyway.... I will keep searching and post here in an effort to help with future questions like mine.

Nope, he is talking about (geometric) roll understeer. He also mentions that a factory suspension used more (geometric) roll US to account for OS from other sources. He does indirectly mention that understeer means the front looses grip before the rear, making it harder to drift.

Roll is not the only factor in understeer, but it plays one of the larger effects, especially when rod ends are used.

In general in 4 link threads, roll OS and OS are the same thing and both are talking about geometric OS.

 

[YeeP]

So, if I understand you correctly, your initial suggestion was a reference to those three statements:

• Rear Roll Axis: Slopes down towards front - understeer
•  Front Roll Axis: Slopes down towards rear - understeer
•   Vehicle Roll Axis: Slopes down towards front- oversteer

In your opinion this combo would be worth the effort. Correct?

 

[Treefrog]

So, if I understand you correctly, your initial suggestion was a reference to those three statements:

• Rear Roll Axis: Slopes down towards front - understeer
•  Front Roll Axis: Slopes down towards rear - understeer
•   Vehicle Roll Axis: Slopes down towards front- oversteer

In your opinion this combo would be worth the effort. Correct?

For something slow, yes. Or slight US for all three, 0-3 degrees.

Honestly, for a crawler that isn't being raced or pushed to the limits in corners, most people probably wouldn't be able to tell the difference between OS and US if they are near 0.

 

[NDCjeepsmith]

Can we get a sticky for this?

 

[dirtzuk]

got some questions about roll understeer and also conflicting anti squat numbers between the old 4 link calculator and the new version.. im building a portal buggy with a 21" belly.. it seems like no matter how I do it I end up with between -6 to -8 roll understeer front and back.. the only way im finding to correct this closer to zero is by tucking the lower links way up ( not ideal as id much rather them line up with the belly for a smooth transition sliding over rocks) ... the other question I had was when building my link setup I used an old version of the calculator and ended up around 65 for anti squat rear aswell as 65 anti dive up front... same numbers punched into the new calculator and im now at 35 anti squat and anti dive.. should I make some changes? my last build was based off the old calculator and worked well at that 65 ish number front and rear so im torn what to do.

 

[Treefrog]

got some questions about roll understeer and also conflicting anti squat numbers between the old 4 link calculator and the new version.. im building a portal buggy with a 21" belly.. it seems like no matter how I do it I end up with between -6 to -8 roll understeer front and back.. the only way im finding to correct this closer to zero is by tucking the lower links way up ( not ideal as id much rather them line up with the belly for a smooth transition sliding over rocks) ... the other question I had was when building my link setup I used an old version of the calculator and ended up around 65 for anti squat rear aswell as 65 anti dive up front... same numbers punched into the new calculator and im now at 35 anti squat and anti dive.. should I make some changes? my last build was based off the old calculator and worked well at that 65 ish number front and rear so im torn what to do.

Regarding the antis, versions 4.0 and up are able to account for 4wd enabled. It's been covered in more depth in some other posts in this thread. The input fields "Drive Bias" and "Brake Bias" are the source of the change. Without changing them the AS and front AL are 50% of the earlier calc values, and AD and rear AL are 60% and 40% respectively.

Pics help, especially with roll stuff. Assuming you are taking about vehicle roll axis, the front roll center is higher than the rear's. Raising one or lowering the other is the solution. Try changing Y values around to do this if its a 4 link. Or raising or lowering the panhard if it is a 3 link.

 

[dirtzuk]

ok that makes more sense ... moving the drive bias to 0 and 100 % spits out the numbers on the old calculator ... here is what im dealing with

 

[Treefrog]

ok that makes more sense ... moving the drive bias to 0 and 100 % spits out the numbers on the old calculator ... here is what im dealing with

Try separating the rear uppers some. Particularly at the axle.

 

[chaplinfj60]

so random thought this afternoon, i was looking at my numbers because i do that once in awhile.
a little over a year back i made my rear drive shaft, we did not use this page of the 4 link calc but my travel distance of my drive shaft was damn near spot on to this chart. i mean we marked the drive shaft and cycled the suspension and measured the travel, and damn its right at 3/4-7/8 inch travel holly buckets thats so darn cool to have the excel sheet validate numbers.. thanks again treefrog.

 

[Treefrog]

so random thought this afternoon, i was looking at my numbers because i do that once in awhile.
a little over a year back i made my rear drive shaft, we did not use this page of the 4 link calc but my travel distance of my drive shaft was damn near spot on to this chart. i mean we marked the drive shaft and cycled the suspension and measured the travel, and damn its right at 3/4-7/8 inch travel holly buckets thats so darn cool to have the excel sheet validate numbers.. thanks again treefrog.

Cool. Nice to see that theory matches reality. If you use it for the front, you will need to go to version 6.10. There was a small mistake in the calculator for front driveshaft travel.