The IFS vs SFA Thread

[evoaire]

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.

First time posting, yeah. This is why.
This is starting to sound like the technical stuff I have been waiting to read. I do hope more is to come. I do lean on the side of SFA. Granted some technical discussion specific to the Bronc is in limbo due to not having more info, ie is it gonna be a boy (SFA) or a girl (IFS) or possibly a girl who identifies as a boy, or some variation of the alphabet group.

So I’m hear to learn and get into wheelen. My question is for the quote above, what is “ TTB on the FSB” ?
Thanks.

Sponsored

 

[TeocaliMG]

First time posting, yeah. This is why.
This is starting to sound like the technical stuff I have been waiting to read. I do hope more is to come. I do lean on the side of SFA. Granted some technical discussion specific to the Bronc is in limbo due to not having more info, ie is it gonna be a boy (SFA) or a girl (IFS) or possibly a girl who identifies as a boy, or some variation of the alphabet group.

So I’m hear to learn and get into wheelen. My question is for the quote above, what is “ TTB on the FSB” ?
Thanks.

as much as I want to come up with a new orientation under the label TTB it means twin traction beam, also known as TIB or twin I beam. It is one version of independent suspension in which the pivot for the control arm or beam lies on the opposite side of the vehicle centerline. This lets the vehicle minimize the scrub and camber change without needing separate control arms to control the wheel camber resulting in a seemingly simple design that looks a lot like a really long solid axle that was cut in half and then overlapped halfway. I have talked earlier about how the simplicity of TTB or SFA is really over blown but regardless they are no doubt very robust and capable for what they are. Oh and as for reduced camber change and scrub through travel they are still pretty bad, it just so happens that it doesn't really matter much offroad at least compared to the other benefits of TTB.

As one of the few proponents of IFS from a performance standpoint I would have loved to see a modern take on the TTB. Just as the SLA (short-long arm) IFS on the Bronco looks to be significantly improved over anything from even just 10 years ago, TTB could have been similarly improved. maybe they could have developed a parallel linkage TTB or some special floating driveline. A guy can dream....

FSB=full size bronco. TTB was also used on the F150 and F250.

 

[Jdc]

as much as I want to come up with a new orientation under the label TTB it means twin traction beam, also known as TIB or twin I beam. It is one version of independent suspension in which the pivot for the control arm or beam lies on the opposite side of the vehicle centerline. This lets the vehicle minimize the scrub and camber change without needing separate control arms to control the wheel camber resulting in a seemingly simple design that looks a lot like a really long solid axle that was cut in half and then overlapped halfway. I have talked earlier about how the simplicity of TTB or SFA is really over blown but regardless they are no doubt very robust and capable for what they are. Oh and as for reduced camber change and scrub through travel they are still pretty bad, it just so happens that it doesn't really matter much offroad at least compared to the other benefits of TTB.

As one of the few proponents of IFS from a performance standpoint I would have loved to see a modern take on the TTB. Just as the SLA (short-long arm) IFS on the Bronco looks to be significantly improved over anything from even just 10 years ago, TTB could have been similarly improved. maybe they could have developed a parallel linkage TTB or some special floating driveline. A guy can dream....

FSB=full size bronco. TTB was also used on the F150 and F250.

I had to do some research on ttb as it's new to me. Just thought it was cool to learn about another suspension setup.

 

[OX1]

Virtual Corona induced, kicking the crap out of IFS again, anyone??

 

[TeocaliMG]

If you guys want to try another thought experiment, try thinking about the objectives of suspension as if you are writing a DFMEA. What are your primary functions? what do you want the suspension to do, and what are the failure modes which would inhibit the function and the associated severity rating? Further you can explore the occurrence and detection of the causes of each failure mode.

So obviously there are fans of solid axles and independents suspensions here, and there are fans of either who have no idea what they are talking about, and there are fans of either who do. So perhaps before anyone takes a side they should clearly define the desired functions, like an engineer would.

For example: I want the knuckles to be constrained to 2 degrees of freedom. Yaw and Vertical wheel path (perhaps tilted back, or arced)

I want robustness in all other degrees

I want each knuckle to have degrees of freedom independent from the others, that is only dependent on the sprung mass dynamics and terrain input. (Now why on earth would I want any degree of freedom to be semi dependent on another? there is no justification for this in function alone.)

Now in the real world we have to make compromises. SLA IFS and SFA are both imperfect systems and do not optimally meet all functions. I think once people think through the desired functions they can more clearly define why they want/need SFA or IFS by function definition and compromise to the inevitable failure to meet all functions.

In short there is no better system than independent. in any condition. for any reason. EVER. THERE I SAID IT!!!

but wait that cant be right? well of course not... how do you actually build an independent suspension... enter the DFMEA process and the long terrible walk of compromises. after which SFA may be your favorite... (but probably still shouldn't be TBH)

P.S. anyone actually read all this? lol maybe I'm going mad with the Rona. I say lets just wait and see how the Bronco does and by the way it does not meet the perfect function either, but then again what does... I think I want my Truck to ride on a force field with no axles at all...

 

[frinesi2]

If you guys want to try another thought experiment, try thinking about the objectives of suspension as if you are writing a DFMEA. What are your primary functions? what do you want the suspension to do, and what are the failure modes which would inhibit the function and the associated severity rating? Further you can explore the occurrence and detection of the causes of each failure mode.

So obviously there are fans of solid axles and independents suspensions here, and there are fans of either who have no idea what they are talking about, and there are fans of either who do. So perhaps before anyone takes a side they should clearly define the desired functions, like an engineer would.

For example: I want the knuckles to be constrained to 2 degrees of freedom. Yaw and Vertical wheel path (perhaps tilted back, or arced)

I want robustness in all other degrees

I want each knuckle to have degrees of freedom independent from the others, that is only dependent on the sprung mass dynamics and terrain input. (Now why on earth would I want any degree of freedom to be semi dependent on another? there is no justification for this in function alone.)

Now in the real world we have to make compromises. SLA IFS and SFA are both imperfect systems and do not optimally meet all functions. I think once people think through the desired functions they can more clearly define why they want/need SFA or IFS by function definition and compromise to the inevitable failure to meet all functions.

In short there is no better system than independent. in any condition. for any reason. EVER. THERE I SAID IT!!!

but wait that cant be right? well of course not... how do you actually build an independent suspension... enter the DFMEA process and the long terrible walk of compromises. after which SFA may be your favorite... (but probably still shouldn't be TBH)

P.S. anyone actually read all this? lol maybe I'm going mad with the Rona. I say lets just wait and see how the Bronco does and by the way it does not meet the perfect function either, but then again what does... I think I want my Truck to ride on a force field with no axles at all...

You lost me at DFMEA. Or I lost it at DFMEA. I'm not sure which.

 

[OX1]

thought

It was a joke dude, but love the passion, LOL!!!

 

[OX1]

Solves one of the issues for solid axle swap.........

 

[Escape_Artist]

Solves one of the issues for solid axle swap.........

What is that off of?

 

[OX1]

What is that off of?

New F250 (maybe 350) with 7.3..................

 

[TeocaliMG]

It is a small supplementary steering system for the superduty, they had a demo on it a while back, pretty clever. It is mounted on the input side of the hydraulic RCB gear so obviously the main steering force is coming from the RCB gear. This just lets the software guys give the steering system some brains, much like the electric racks in the F-150/Ranger

Pretty awesome!

 

[BAUS67]

………………………... This just lets the software guys give the steering system some brains, much like the electric racks in the F-150/Ranger

Pretty awesome!

LOL so big brother can drive for you so you can text.

 

[OX1]

LOL so big brother can drive for you so you can text.

I was thinking more so all the nanny systems are happy and don't go into
"deputy droop along" mode...........

 

[Broncosaur]

LOL so big brother can drive for you so you can text.

or if it gets stolen, it will drive directly to the police station,after locking the thief inside of course.

 

[OX1]

or if it gets stolen, it will drive directly to the police station,after locking the thief inside of course.

That going to be rough on a soft top................ (or no top)

Sponsored