Low CG, max articulation, and biggest tire size without interference?

[sfonteno]

Been a while since I read all the replies, I've been out wheeling and camping having a blast.

Some of my opinions on the sway bar discussion. With modern vehicles the weight balance is EXTREMELY front loaded. Just take a look at the spring # front and back with yota's and ford's. The Bronco is no exception from what I've seen. A rear sway bar is a must, without it the IFS isn't going to flex for shit. You'll max out the rear, and then get all kinds of wheel lift and body roll. The rear needs to roll the front, unless you go mess with suspension spring and shock rates, removing the rear and leaving the front will be even worse imo.

Got my truck on a ramp, which I could care less about the RTI value, I was more interested in the wheel lift I could get, which is useful to know out in the wild.
Stock sasquatch with no front sway bar was a 19 inch vertical wheel lift (RTI 478), bleh.
Updated build was 24 inches vertical wheel lift (RTI 604), WOOOO

Summary of where my build is at suspension wise:
With the badlands suspension, rear 1/2 spacer, front and rear 1.5 inch preload perch collars (Yes, the ones listed as "front" are on the front and back hence the spacer.), and I took an inch off all of the bump stops front and back, kept rear sway bar, removed front sway bar.

Took the truck out with my teardrop to Buena Vista, CO Fourmile trail area, had an amazing time, was able to park my teardrop in areas no one else could park at. Even got a comment from a Razor guy asking how I got back there lmao. The truck continues to amaze me at how easily it handles whoops, rocks, mud, water, etc. I'm totally sold on IFS over solid axle up front on everything except rock crawling buggies. For non-rock crawling trails it just is super stable. (Drives like Spiderman climbs on all fours.)

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[Rkgzx9leftcoast]

Been a while since I read all the replies, I've been out wheeling and camping having a blast.

Some of my opinions on the sway bar discussion. With modern vehicles the weight balance is EXTREMELY front loaded. Just take a look at the spring # front and back with yota's and ford's. The Bronco is no exception from what I've seen. A rear sway bar is a must, without it the IFS isn't going to flex for shit. You'll max out the rear, and then get all kinds of wheel lift and body roll. The rear needs to roll the front, unless you go mess with suspension spring and shock rates, removing the rear and leaving the front will be even worse imo.

Got my truck on a ramp, which I could care less about the RTI value, I was more interested in the wheel lift I could get, which is useful to know out in the wild.
Stock sasquatch with no front sway bar was a 19 inch vertical wheel lift (RTI 478), bleh.
Updated build was 24 inches vertical wheel lift (RTI 604), WOOOO

Summary of where my build is at suspension wise:
With the badlands suspension, rear 1/2 spacer, front and rear 1.5 inch preload perch collars (Yes, the ones listed as "front" are on the front and back hence the spacer.), and I took an inch off all of the bump stops front and back, kept rear sway bar, removed front sway bar.

Took the truck out with my teardrop to Buena Vista, CO Fourmile trail area, had an amazing time, was able to park my teardrop in areas no one else could park at. Even got a comment from a Razor guy asking how I got back there lmao. The truck continues to amaze me at how easily it handles whoops, rocks, mud, water, etc. I'm totally sold on IFS over solid axle up front on everything except rock crawling buggies. For non-rock crawling trails it just is super stable. (Drives like Spiderman climbs on all fours.)

So are you saying you cut your bump stops down between the 2 tests? If so im guessing where most of your flex increase is coming from?

I dont think the rear sway bar is big enough diameter to push the front down more. It may help with sway in the rear, but to effect travel in the front..... I dont think I would say it does that?

I know in NASCAR and other forms of racing they use bars up to 2in in Diameter in the rear to do what your saying.... not sure the 5/8 or whatever ours is would do the same. Maybe unhook the rear links and do another test.

 

[sfonteno]

So are you saying you cut your bump stops down between the 2 tests? If so im guessing where most of your flex increase is coming from?

I dont think the rear sway bar is big enough diameter to push the front down more. It may help with sway in the rear, but to effect travel in the front..... I dont think I would say it does that?

I know in NASCAR and other forms of racing they use bars up to 2in in Diameter in the rear to do what your saying.... not sure the 5/8 or whatever ours is would do the same. Maybe unhook the rear links and do another test.

The badlands suspension also has more travel from what I measured.

The rear sway bar is an inch I believe, and when you talk about corner to corner articulation it doesn't take much to overpower the rear springs.

If it's around an inch you are talking 1000-2000 pounds so I am not sure why you are saying that won't effect it, it's going to be around the weight of the engine to offset that giant weight being thrown around at the front of the car.

 

[Rkgzx9leftcoast]

The badlands suspension also has more travel from what I measured.

The rear sway bar is an inch I believe, and when you talk about corner to corner articulation it doesn't take much to overpower the rear springs.

If it's around an inch you are talking 1000-2000 pounds so I am not sure why you are saying that won't effect it, it's going to be around the weight of the engine to offset that giant weight being thrown around at the front of the car.

Ive looked at mine, I dont believe its an Inch, looked smaller to me? I believe the front is only 1-1/8in or so . never thought to measure it. If one side in the rear is maxed out up travel wise the opposite corner of the front would be pushed down either way . Like when people test flex with a fork lift.

Not saying you are wrong...... Like I said , disconnecting it and testing it both ways would tell the tale.

 

[87-Z28]

Once you change the geometry of the a-arms themselves (in this case by making them longer), shock travel and wheel travel measurements aren't an apples to apples comparison to stock anymore. What I can't find out about this kit is if the Kings used are the same exact shock specs that already bolt on to the Bronco...I'm assuming they are, but it's possible that King has made a longer travel shock for these guys (would be great if they did). Generally you go longer with the a-arms for two reasons, to alleviate binding from the axle/tie rods/ball joints etc. in order to net more travel at the wheel, and also to add room for longer shocks (couple this with a higher shock tower and you technically have a long travel suspension). Using short travel shocks on a +3 kit sounds like a lot of potential wheel travel thrown away, and 11" of wheel travel isn't really something to write home about for extended a-arms. It's entirely possible that this kit could get more travel with nothing more than a better shock option, but I wouldn't bank on it.

Not apples to apples. Need to know motion ratios to do proper comparison. On the bronco stock front suspension, I think the motion ratio calculates as shown. Can be estimated as length of LCA divided by radius of shock attachment or 15”/10”=1.5. King shocks advertise 6.1” of travel so 9.1” at wheel (6.1*1.5). Increasing LCA length by +3” roughly increases motion ratio to 18”/10”=1.8. Only a 20% increase over stock or 1.8/1.5=1.2. So short travel king shocks only get you 6.1”*1.8 or 11” of wheel travel. Heck the stock bilsteins get 6.25” of travel.

Of course don’t need all the math to know 11” at wheel is not that great, as Tex said. For our front end, +3” on LCA only gets you 20% more and adds 6” of width. A lot left on the table without going to longer travel shocks with higher mounting.

 

[87-Z28]

Does anyone have any real numbers on front sway bar deformation? If SAS has 9” of wheel travel and you’re sitting with 4 up and 5 down at ride height. Doesn’t seem like sway bar can deform elasticly more than 2-3” per side? No idea? Maybe only 4-6” of relative wheel articulation???

Just talking about the stock theoretical sway bar deformations, nothing else in the system. Trying to isolate effects of sway bar. Clearly you can take a forklift and lift a single front wheel deforming the entire complex load path through out the vehicle. Sway bar is only a part of that, springs deforming in series; tires, front shock springs, bushings, sway bar, frame flex, load transferred to rear suspension and all subsequent rear suspension deformations.

reversing sway bar loading when needed is a brilliant idea, especially if that can be done robustly with gears and a locker. Seems like a very simple but elegant solution. A lighter sway bar can surely be designed, especially if TEX is driving around without one. But reversing is best of both worlds.

 

[Tex]

Does anyone have any real numbers on front sway bar deformation? If SAS has 9” of wheel travel and you’re sitting with 4 up and 5 down at ride height. Doesn’t seem like sway bar can deform elasticly more than 2-3” per side? No idea? Maybe only 4-6” of relative wheel articulation???

Just talking about the stock theoretical sway bar deformations, nothing else in the system. Trying to isolate effects of sway bar. Clearly you can take a forklift and lift a single front wheel deforming the entire complex load path through out the vehicle. Sway bar is only a part of that, springs deforming in series; tires, front shock springs, bushings, sway bar, frame flex, load transferred to rear suspension and all subsequent rear suspension deformations.

reversing sway bar loading when needed is a brilliant idea, especially if that can be done robustly with gears and a locker. Seems like a very simple but elegant solution. A lighter sway bar can surely be designed, especially if TEX is driving around without one. But reversing is best of both worlds.

Maybe the place to look for that answer would be the torsion bar setups that GM used for a while. They were a bit longer than the swaybar but not by a whole lot, and thickness is similar from what I recall. They were twisted considerably bump to bump, and were even preloaded with some deflection already added. I would imagine the swaybar is going to be made from a similiar if not identical alloy as a torsion bar. You'd basically be adding the moment arm of the swaybar arm to the moment arm of where it bolts up to the LCA about halfway out to the wheel to get a figure that would represent actual deflection from bump to bump. They probably have a lot more ability to twist than what we're putting on them.

One thing's for sure, they don't need that thick of a swaybar up front, it's entirely overkill.

 

[87-Z28]

Yeah agree. It wouldn’t be designed to torque up near the plastic limit. Probably a safety factor near 2, so at best we are pushing sway bar to 50% of its elastic limit. I can calculate moment arms. Need a good wall thickness. Material is less of an issue. Steel elastic properties are fairly consistent. Thanks for help.

for direct replacement the moment arm geometries won’t change, so bar diameter and wall thickness are critical variables. Very curious what stock effective torsional spring stiffness works out to be. If I can find some time I will try to run down some numbers.

 

[Tex]

I could get you a min/max diameter for the bar if you'd like, and length between bushings too, it's just sitting against the wall collecting dust. I've considered re-installing it with the new walker link setup, simply because I've never had a chance to see what a dampened swaybar feels like, and the possibility of using it in conjunction with a reverse swaybar might be interesting.

As for wall thickness, my guess is that it's solid due to the way it's made. Hollow swaybars are generally straight splined sections similar to what desert trucks run and look like gun drilled axleshafts....which, they basically are, as a lot of them are 35 spline with similar measurements. Since gun drilled axles have about the same torsional rigidity as their solid counterparts, I doubt the calculations would be all that much different. Also keep in mind this is for the solid bar, not the badlands, which are completely different in design.

 

[87-Z28]

I took mine off yesterday. It attaches a little over 9” from LCA pivot so motion ratio wrt wheel is about 1.6. It has a bit more leverage than the shocks do. It sure does feel solid, surprised by how much it weighs. Taking some more exact measurements today.

It feels a bit off to me driving without it, maybe just in my head. I have digressive bilstein 6100s on so that probably helps. Need more road time.. But my other car is a BMW 328. So not sitting a few inches of the road is new to me.

I will play with it. that’s part of the fun. Thanks for all of the insight.

did you ever redrill the lower rear shock mount? How high did you go and did you keep it along shock axis?

 

[87-Z28]

Some sway bar math. This analysis considers resistance of sway bar only and provides some insight into sway bar behavior as related to its diameter.

A simple approximation for the anti-sway bar flexibility/rigidity (solid bar), is the diameter to the fourth power. A very strong relationship. The solid front bar on my OBX is 1 3/8” from the factory. So decreasing bar diameter to 1 1/4” results in 46% increased flexibility. Notice just 1/8” decrease in diameter has a significant affect. A 1” bar has 350% increased flexibility, that is getting real.

This begs to question if a 1” bar will have any real anti-sway resistance. Does it serve any purpose? If you strap on a 16 gage wire as a sway bar obviously there will be no anti-sway benefit, but also no hindrance to flex or articulation either. Ultimately not worth the effort. So clearly there is a minimum sway bar diameter to achieve any real benefit. What is that number?

A more detailed and thorough analysis of the sway bar resistance wrt the forces generated in the sway bar links is shown. Sway bar link forces are required to generate anti-sway resistance, but they also limit articulation or relative wheel travel between front two wheels. Up on one side and down on the other.

The analysis includes sway bar resistance from main bar torsion, torsion of ends, and bending of ends. Essentially five springs in series between the two sway bar links. The analysis shows that torsion of main 34” long section dominates. See first figure. Plotted is the relative sway bar link motion with respect to sway bar link forces. Sway bar links have some leverage wrt wheel motion due to their attachment location on LCA, approximately a 1.75 motion ratio.

So for different bar sizes (diameters) the sway bar forces wrt wheel motion can be plotted, see remaining figures. Shown are the OEM diameter of 1 3/8” compared to 1” bar. As estimated earlier, 1” bar is more flexible by a factor of near 3.5. So for the same resistance or force in the links, relative wheel motion is 3.5 times greater.

Considering a 4” relative wheel displacement at >60 mph to be a fairly serious sway event. Then the stock oem bar can produce 1500 lbs of resistance, whereas 1” bar only produces about 400 lbs of resistance. Is that enough to calm down sway? Not sure, but with a roof top tent and heavily loaded, maybe not.

Also shown on the plots are the “walker” damper links which provide about 1.5” of travel at each wheel, so call it 3” total. For Walker links you will be near yellow curve for slow speed articulation (no damping force). And near blue curve or stock curve for high speed anti-sway.

It seems a 1” bar may be very beneficial towards flexibility, but again not sure if it will provide any real anti-sway benefits. Would be interesting to try out. I am not convinced. Maybe better to just use mechanical release (PITA) or drive without sway bar. Walker damping links seem to be a promising alternative, but will ultimately still limit max articulation.

Also shown are comparisons of 1 1/8” bar with stock and 7/8” bar. Most interesting and promising bar in my opinion is a 1” bar. A 7/8” bar doesn’t have much anti-sway value, and 1 1/8” bar is not flexible enough.

 

[87-Z28]

Adding some context to the sway base link forces so the curves can have more meaning. @Tex or @Snacktime if you guys have some better numbers or experience with link forces please add thoughts.

I attached some actual measured shock data from accutune offroad. Might not be exactly tuned for 6g bronco but does give an idea of shock forces. See figure. A violent high speed sway event will likely occur for shock velocities of >25 in/sec, and probably >50. From the shock curves a good digressive valving will produce >1000 lbs to resist such velocities, >500 lbs for linear shocks.

assuming shocks alone can’t resist sway effectively, then sway bar forces need to add additional resistance. It is likely that >500 additional lbs force is needed to calm down a violent sway event, just based on shock curves shown here. Possibly up to 1000 lbs, or double what digressive shocks alone can provide.

stock sway bar can easily add >1000 lbs of anti sway forces. A 1” bar will struggle to add >500 lbs of force. See previous post.

 

[Tex]

So, when I get my Bronco into a situation where it will develop a sway oscillation, it happens in very specific circumstances (namely, above 50mph, under acceleration, then add lateral force from turning or a lane change). When that occurs, it's not even close to reaching 4" of movement in the suspension. It's about like standing next to it and rocking it back and forth by hand, it might be something like 1-2" of movement. My opinion in the matter is that the swaybar is able to resist the oscillation by only allowing a small amount of deflection, essentially if it can reduce body roll by 1-2", then it can eliminate the oscillation entirely by not allowing the conditions to occur. I don't actually know this to be fact, however, since I haven't driven with the swaybar since I installed all the heavy bumpers and tire carrier and gas cans etc. But, given how specific the conditions have to be for it to happen, and how easy it is to interrupt the oscillation by reducing power or changing lateral loading, I'm confident that it would only need a percentage of what the OEM swaybar provides.

More than anything, the swaybar is to keep body roll minimized, as keeping it upright increases both traction and stability. It's not really intended to prevent sway oscillations as that *should* be the job of the shocks alone (and overall weight distribution/stability of the vehicle)...however, when the sway bar is effective enough to virtually eliminate body roll, it also has the benefit of eliminating any oscillations that the shocks are otherwise incapable of handling. Ultimately, a lot of people aren't used to body roll in any capacity, and I believe that's the primary driving factor in why they took such a heavy handed approach with the swaybar. A vehicle that doesn't sway at all feels especially solid with good road manners, but it's not necessary to completely eliminate sway for traction and stability benefits, not even in a race car. Perhaps they were expecting people to add a lot of weight to the roof and they wanted to size the swaybar for the worst possible conditions, honestly I couldn't say.

I do intend to re-install the swaybar if I take my Bronco up to the midwest here in a week, so I might be able to add some more insights on that 1200 mile trip.

 

[Snacktime]

@87-Z28 I got a few new flap disk for my grinder. I might re profile my sway bar after I do my bumper.

 

[87-Z28]

Yeah. I think you’re right. The factory sway bar was designed to mitigate body roll so the Bronco feels more stable to the SUV crowd. The OEM bar can quickly apply >500 lbs of load, even for 1-2” of body roll. Ford also wants to sell their fancy electronic disconnect, product line differentiation.

A 1” bar will apply 3.5x less load, and will struggle to get >200 lbs of resistance for 2” body roll. Especially when considering other “soft” flexibility in the load path such as air pressure in tires and bushings.

Maybe 1” bar would be fine, especially with some good digressive shocks. But I think you would feel the initial body roll and that is what Ford was trying to mitigate. The walker links give you a free 3” of articulation but then behave like stock. The 1” bar provides greater articulation than the walker links once you get past 4-5 inches. I bet you get close to 19” doing the forklift thing with a 1” bar.

Maybe snacktime will go down to around 1” and do some field testing. I saw that Carli suspensions was making a sway bar. I sent them an email trying to see what bar diameter they were considering.

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