The IFS vs SFA Thread

JimmyDean

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I feel like this is a code of some sorry but I can’t decipher it.
Well, slick starts with an 's', so does solid
forcing starts with an 'f', so does front.
backpedal has an 'a' in it, as does axle

so I'm going with code for 'Solid Front Axle'.
 

BAUS67

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I like where you're headed with this. Tell me more about how one would do the swap.
If I was to try and convert an IFS Bronco to SFA :wink: I would use wat is already available to me :wink: That would make most people happy and would not be a huge expense in R&D. :rockon:

On a bit more serious note I have not seen how the Troller suspension is, but if I was to build from scratch it would be triangulated 4 link rear and 3 link front.

I just knew Ford would NOT disappoint.:please: Let it be true.
 
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OX1

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Why not both?
At some point, your just way too high for overall stability.
My 79 is really too tall for severe side-hilling. But I can take
stupid lines on big rock, less than straight up, climbs.
 

TeocaliMG

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Been a while since I visited this, good to see we have a dedicated thread!
1581706927610.png


Anyway, for any new guys who are remotely interested in the discussion (old timers too I guess) The next time the glories of SFA come to mind, or the woes of IFS I want you to think about why, exactly why, and if you can put it into words, try it here. I will make no claim that a typical IFS (in stock form) will out perform SFA (in stock form) in HARDCORE rock crawling. My claim is that IFS (yes even a stock offering) can be made way more competent off-road than it is given credit for, and yes I am not talking about high speed desert running where the results are obvious. Regardless of what we get with the Bronco, SFA, IFS, or both, this is true.

So with that said, why is SFA absolutely mandatory to you guys? I don't mean that rhetorically, I mean specifically, what technical reason exists that requires this? I know there are some, but I want to hear you say them, think through it, there may not be as many as you think. That is what I am trying to gauge here. There is no way that IFS can be the cost efficient solution for everyone (meaning 100%) but my guess is we disagree on whether the opportunity lost is 25% or less than 5% or maybe less than 1%

Something I would like you guys to consider: If your vision for your Bronco is tires significantly bigger than 37", those puppies better be on some serious axles, and those axles better be pinned down by some serious joints, links, mounts. You get the picture. When you think of your dream Bronco vs your Dream Jeep, what even is stock anymore? -I bet you the answer is a lot closer than you might think, and whatever stock remains, the Bronco will have no issue delivering on.


Also for those who would like to entertain a conversion anyway, I have an interesting idea about a pseudo SFA conversion which would let you keep a ton of stock IFS architecture (ironic I know)
 

ChrispyKC

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Good stuff happening here.
 

BAUS67

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Been a while since I visited this, good to see we have a dedicated thread!
1581706927610.png


Anyway, for any new guys who are remotely interested in the discussion (old timers too I guess) The next time the glories of SFA come to mind, or the woes of IFS I want you to think about why, exactly why, and if you can put it into words, try it here. I will make no claim that a typical IFS (in stock form) will out perform SFA (in stock form) in HARDCORE rock crawling. My claim is that IFS (yes even a stock offering) can be made way more competent off-road than it is given credit for, and yes I am not talking about high speed desert running where the results are obvious. Regardless of what we get with the Bronco, SFA, IFS, or both, this is true.

So with that said, why is SFA absolutely mandatory to you guys? I don't mean that rhetorically, I mean specifically, what technical reason exists that requires this? I know there are some, but I want to hear you say them, think through it, there may not be as many as you think. That is what I am trying to gauge here. There is no way that IFS can be the cost efficient solution for everyone (meaning 100%) but my guess is we disagree on whether the opportunity lost is 25% or less than 5% or maybe less than 1%

Something I would like you guys to consider: If your vision for your Bronco is tires significantly bigger than 37", those puppies better be on some serious axles, and those axles better be pinned down by some serious joints, links, mounts. You get the picture. When you think of your dream Bronco vs your Dream Jeep, what even is stock anymore? -I bet you the answer is a lot closer than you might think, and whatever stock remains, the Bronco will have no issue delivering on.


Also for those who would like to entertain a conversion anyway, I have an interesting idea about a pseudo SFA conversion which would let you keep a ton of stock IFS architecture (ironic I know)

I saw this at work today and had to wait till I got home to tackle it, but I want to first say, this is not easy to do without typing a mile long explanation and I tend to get off track explaining my perspective (why I see it the way I do). so bear with me and I will give a try. This is all just my opinion and comes from me doing dumb stuff when I young, dumb, and full of cum. No college grad, just a simple guy who loved fast cars and off-roading. Drag racing will teach one a lot about how a suspension reacts to power input and traction. Had a guy tell me one time that Detroit lockers were junk because he had one in his CJ and when confronted on a gravel road with a driver in his lane he ended up over the bank. But I enlightened him on what happens when you "snap on" or "snap off" the gas when having a "locker" in the rear vs. having a limited slip. but here again that is for another day. As I have stated before I will buy a Bronco IFS or SFA just because I'm a Ford guy who bleeds Ford blue and it is cooler than my Explorer and more capable. The question for me is will it have a SFA as an option. Another point is that one always has to consider Murphy's Law and physics when looking at this they have an effect that is hard to explain.

the following is in not particular order and not defined by stock vs. modified just general statements.( we can get specific later)

SFA advantages:

Basic design, inexpensive/easily lifted or modified/upgraded

Better turning radius due to A-arms not being in the way and not to mention that U-joint tech has raised the bar by creating a new u-joint that has increased the turning radius by 3 degrees.

more articulation …… this is difficult to explain by typing, the motion of one side affects the other side this doesn't happen in the same manor as with IFS. Yes I know both wheels are still connected by the diff but one moves independent(IFS) and one moves because the other one is telling it to(SFA). It is like a giant lever.( my drawing elsewhere in this forum does a good job at showing what I mean)

SFA disadvantages:

ride quality ( I use this because everyone else does but is not how I like to say it) I like Ride Control. because honestly ride quality to me is more just a shock thing making your ride smooth. Ride control is the suspension controlling the environment it is traversing. Things have come along way lately but with not many SFA vehicles it has fallen on the aftermarket to improve the SFA's ability to control the ride at speed. By mounting the shocks reward of the axle and not on top sown good results. I have even noticed that the IFS cars are doing this now. They used to have them in the middle of the A-arms and now they are behind (that makes the A-arm narrower for better turning radius) the shocks are angled inward at the top.

this is getting long and I am sure I will remember stuff later so I guess this will be the ones I can think of now ……..

should have done it on paper first HAHA :crazy:


IFS advantages:

ride quality (had to give this some though so its not so long) Best way to put is buy watching the whoops section. IFS can handle this in the best way because it travels independently of each side. SFA when one side is being pushed up it wants to push the other down and if no whoop you are ok but if you are starting up a whoop then you are fighting the force coming from the other side as well. Hard to describe in type, better to watch video.(I'll try to find something).


IFS disadvantages:

lots of moving parts. (forgot this as an advantage on SFA) look at it this way. SFA has one u-joint at the axle end for turning the IFS has one inner and one outer joint for turning and suspension travel. see where I'm headed with this.

expensive to modify (lift kit/ taking 37's) IFS has the front diff mounted to the frame by crossmembers which also serve as mounting points for the lower A-arms (most cases). To "lift" this design you must lower those crossmembers and diff much more labor intensive. Most parts to upgrade for bigger tires are $$$ when compared to SFA's junkyard and a welder approach.

how this for a start for now I'll be sure to keep a notepad with me and give myself reminders and will return with more I'm sure. It sucks getting old guys just for the record just seems like the are not enough hours in the day anymore. 30 years ago I had all the time in the world, now it just flies by. Until then ..............



:rockon:
 
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JimmyDean

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I saw this at work today and had to wait till I got home to tackle it, but I want to first say, this is not easy to do without typing a mile long explanation and I tend to get off track explaining my perspective (why I see it the way I do). so bear with me and I will give a try. This is all just my opinion and comes from me doing dumb stuff when I young, dumb, and full of cum. No college grad, just a simple guy who loved fast cars and off-roading. Drag racing will teach one a lot about how a suspension reacts to power input and traction. Had a guy tell me one time that Detroit lockers were junk because he had one in his CJ and when confronted on a gravel road with a driver in his lane he ended up over the bank. But I enlightened him on what happens when you "snap on" or "snap off" the gas when having a "locker" in the rear vs. having a limited slip. but here again that is for another day. As I have stated before I will buy a Bronco IFS or SFA just because I'm a Ford guy who bleeds Ford blue and it is cooler than my Explorer and more capable. The question for me is will it have a SFA as an option. Another point is that one always has to consider Murphy's Law and physics when looking at this they have an effect that is hard to explain.

the following is in not particular order and not defined by stock vs. modified juts general statements.( we can get specific later)

SFA advantages:

Basic design, inexpensive/easily lifted or modified/upgraded

Better turning radius due to A-arms not being in the way and not to mention that U-joint tech has raised the bar by creating a new u-joint that has increased the turning radius by 3 degrees.

more articulation …… this is difficult to explain by typing, the motion of one side affects the other side this doesn't happen in the same manor as with IFS. Yes I know both wheels are still connected by the diff but one moves independent(IFS) and one moves because the other one is telling it to(SFA). It is like a giant lever.( my drawing elsewhere in this forum does a good job at showing what I mean)
To add, all suspension travels are limited by the length of the arms (on all suspensions) and driveshaft angles on solid axles and CV angles on IFS. on IFS, the arms are from center out, which means that the arms can be no more than less than half the width of the vehicle in a perfect setup. Youcannot achieve a perfect setup on a street vehicle as it has frame rails which are going to be 2' - 3' apart. that is also space taken up the arms can't be longer than. So, on a narrow frame vehicle, with 72" width, you are looking at arms that can be no more than 16" or so in length. this gives a travel range of around 10" when you run the angles. There is zero possibility to increase this travel/articulation any. Maybe you can squeeze it up to 12" or so. Most factory setups are going to be running A-arms closer to 10-12" because the frame rails are further apart for crash safety reasons, limiting travel more.

on an SFA the arms are connected to the frame back behind the axle, and are typically from a factory about 24"-30" in length, and it is very easy to modify them to be half the wheelbase in length (technically could go longer, but generally you don't want front and rear arms to cross due to articulation bind). This provides factory travels of 12"+ minus the shocks and springs. Granted, most factory SFAs are a 3-link, and run radius arms that have two connecting points on the axle which limit the travel through bind, but this is intentional. changing out the factory radius arms for a tube arm with heim joints increases the travel significantly. In short frame vehicles, like the Bronco, and the FSB, and the Jeep, the shortness of the driveshaft from T-case to diff is what is limiting the travel, and there is zero to be done with that short of going with drop T-cases (which is still easier than lengthening travel significantly on an IFS). and on these really short wheelbase vehciles, the front is capable of alot more travel and articulation than the rear when 4-linked. On a 3-linked IFS or coil solid rear with panhard, you do generally LIMIT the travel intentionally to reduce power/brake steer as when travel increases the side to side movement is increased significantly.

On articulation, when you tuck a wheel on an IFS, it literally takes all of the increased forces and removes equal weight on the contact patch of the opposing tire. On an SFA since the fulcrums are between the wheels (the spring mounts), as you tuck a wheel, it adds a fraction of the force to the opposing wheel, allowing for more solid traction throughout the travel range.

On strength, the CV joints, or double u-joints in some designs, of an IFS, and a number of increased fail positions that go through a significantly larger duty cycles then SFA/SRA u-joints. They also cannot be designed to be as robust due to a more limited operating enviroment as compared to the u-joints on a drive shaft which has more real-estate. The u-joints on most SFAs can be more robust as it is given the area inside the hub pivots, and the angles of it do not change with travel/articulation, only while turning (IFS joints will see increased angles or torques during both turning and travel) SFA axles can be more strongly supported as being incased in a, well, solid housing for the entire length.

Now, IFS certainly has it's places, adjust-ability, less unsprung weight, the ability to travel through camber independently, something SFAs cannot do and makes them suffer during handling exercises. and vertical compactness (the hub on an IFS can be horizontal from the frame, or even higher than the frame, on a solid axle the axle has to be below the frame....I guess technically you can go above, some hot rods/rat rods with I-beams do this, but that is for only show car use). For high speed use, or strictly road use, IFS is hands down better than solid axles. but high torque, low speed, high travel/articulation, SFA wins. And that's before discussing costs.

The TTB on the FSBs is an interesting middle ground case that got rid of the short arm length issue of the IFS...but it introduced it's own problem with camber through travel range due to this. IF you were building an IFS rig with about 12+ inch of lift, and a subframe, you could probably get arm length of 2'+, maybe even 3' on a vehicle the width of a full size truck, and increase travel to the 16" range, but you would have to relocate the diff as well.
 

BAUS67

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AWESOME points,you are better at this than I am !:like:

I posted this before I was done to see if it looked right on the screen so I added some from when you saw it first. HAHA sorry I'm not computer savvy and I didn't want it to look like shit !!
 

JimmyDean

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AWESOME points,you are better at this than I am !:like:

I posted this before I was done to see if it looked right on the screen so I added some from when you saw it first. HAHA sorry I'm not computer savvy and I didn't want it to look like shit !!
eh, you highlighted t he key and most important points tbh. My background is engineering, so I tend to go too far in depth of things like this.

I DO NOT want anyone to think I do not like IFS, or think that I think IFS is incapable. It is simply that each is better it certain enviroments, and the (imho) enviroment that the Bronco is designed for, SFA is the better option. heavy trail use and mud and large tires. SFA is also good in heavy duty service, ala heavy towing. anything over about 10 mph outside of mud and heavy payloads and towing, IFS is the better choice most of the time.
 

BAUS67

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eh, you highlighted t he key and most important points tbh. My background is engineering, so I tend to go too far in depth of things like this.

I DO NOT want anyone to think I do not like IFS, or think that I think IFS is incapable. It is simply that each is better it certain enviroments, and the (imho) enviroment that the Bronco is designed for, SFA is the better option. heavy trail use and mud and large tires. SFA is also good in heavy duty service, ala heavy towing. anything over about 10 mph outside of mud and heavy payloads and towing, IFS is the better choice most of the time.

Well said. :like:
 








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