The IFS vs SFA Thread

[BAUS67]

Super Duty SFA expensive because it is Dana 60 stuff. BEEFY = $$$$$ . But IFS beefy is = $$$$$$$$$$$$$ X2

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[BAUS67]

I just think it is ironic because people always say about the "ride" and to me a SFA does not ride that bad. Its supposed to be an off-road vehicle I didn't buy it to take on a trip across the country. That said I did drive my TJ to Houston TX, from PA, and didn't hate it. Much smoother in my Explorer though.

 

[Jalisurr]

Don't think it improves ride quality as much as IFS, for the cost. Possibly a little higher towing and cargo capacity with SRA also.

IRS gives better handling to a certain degree, but as Teocali mentioned, not nearly the same difference the front suspension makes. Because the rear is 'trailing' in a SRA system and doesn't have a direct link to the steering, it ends up working quite well even at speed offroad. Big bumps are 'pulling' on the links rather than 'pushing'. Most trophy trucks are IFS/SRA for that reason. The only real offroad competition that I can think of where IRS is prevalent is the Dakar.

Where switching to IFS gives far better handling at any sort of speed on any terrain, switching to IRS would mostly only benefit bumpy tarmac or washboard gravel, likely at the cost of reduced towing capacity.

 

[BAUS67]

Hence the only real benefit of IRS over SRA is high level vehicle handling.

And not to sound like I am trying to argue but that is my point about the front. To me the IFS is only better because of handling. It sure 'aint because it is easy to modify, or cheap for that matter.

 

[The Pope]

Now, all that said I would expect the Bronco IFS to be a whole other level above the explorer, and it is. Would I also like to see beefier hubs and high clearance arms? heck yea! but that costs money too, if it didn't, then things like the JL would launch with full floaters for example.

Full Floaters!!!!! We're getting a Full Floater SRA!!!! ..................... just kidding, but it would be awesome if we did and that would definitely be a feature that would help the BroncoBronco overtake the Wrangler.

 

[BAUS67]

……………………..
likely at the cost of reduced towing capacity.

So what you are saying is it is stronger. ?? I believe that is my point about a SFA being stronger than IFS. Like I said we all want our cake and eat it too. (no chairs ……….. please)

 

[Jalisurr]

So what you are saying is it is stronger. ?? I believe that is my point about a SFA being stronger than IFS. Like I said we all want our cake and eat it too. (no chairs ……….. please)

Shouldn't be any chairs happening in this thread, those are for when the discussion spills out into...everywhere else...

I would hesitate to say that solid is always stronger (plenty of weak solid axles out there), but I certainly agree that it's easier to make a strong solid axle than a strong independent suspension design. In the rear the handling tradeoff isn't enough to be worth changing to independent for most trucks or SUVs, in the front it is.

I also won't contest it's easier/cheaper to modify a solid axle...IF the modifications we're talking about are lifting it and putting on big tires. However if we're talking about modifying it to go fast over bumps...gonna be much easier if you started with independent and can just swap coilovers and control arms.

Again, I've never said that those who want big tires, going slow over rocks or through mud are wrong for wanting solid axles. It's just not what interests me in an off-road SUV and the point that I will always argue is the notion that the Bronco needs to have a SFA to be successful.

 

[JimmyDean]

Cost is very complicated, in my experience with Superduty SFA can still be VERY expensive to fix/maintain, at least when you do it according to OEM standards. Granted it is cheaper to do most common modifications, I am not convinced it is much cheaper from the OEM, if it is, it is easily outweighed by other attributes both on and off road.

As much as I rave about IFS over SFA in general, the comparison is a lot murkier when comparing IRS and SRA. A lot of the vehicle dynamics that make SFA nearly hot garbage at anything over crawling speed become beneficial on the rear, mainly the huge arcing axle path, (and anti-squat and a host of other things). IRS can also achieve this but it is a harder sell from a wheel travel/arc path quality standpoint. Hence the only real benefit of IRS over SRA is high level vehicle handling.

For example I am not entirely sold on IRS for my dream off-road build. I have two competing ideas, a design for IFS/IRS which allows crazy articulation via some creative changes to the driveline/subframe or a linkage geometry for SRA which has more inherent anti'roll at speed without compromising articulation at low speed (without the need for sway bar or sway bar disconnect)

if you want to get crazy with theoretical anti-roll design, what about long travel magnetic-ride controlled shocks? programming for such could be so that as speed increases it increases dampening to reduce body roll while still allowing significant articulation at lower speeds, or that as long as both sides are trying to travel in the same direction it decreases damping, but if they are attempting to travel opposite (one up, one down, i.e. roll) it tightens it up?

of course, while we are at it, we could look at combining air ride to change spring rate, or go with magnetic springs as well, or using springs contained in a jackscrew so that we can adjust preload on the spring during the drive. getting that to change quickly without causing significant issues may be problematic however. I think that air ride or magnetic springs (in addition to magnetic shocks) would be the best route for a high tech jack of all trades and master of all as well 4x4 setup.

 

[frinesi2]

if you want to get crazy with theoretical anti-roll design, what about long travel magnetic-ride controlled shocks? programming for such could be so that as speed increases it increases dampening to reduce body roll while still allowing significant articulation at lower speeds, or that as long as both sides are trying to travel in the same direction it decreases damping, but if they are attempting to travel opposite (one up, one down, i.e. roll) it tightens it up?

of course, while we are at it, we could look at combining air ride to change spring rate, or go with magnetic springs as well, or using springs contained in a jackscrew so that we can adjust preload on the spring during the drive. getting that to change quickly without causing significant issues may be problematic however. I think that air ride or magnetic springs (in addition to magnetic shocks) would be the best route for a high tech jack of all trades and master of all as well 4x4 setup.

What you're looking for is called a Hydraulically Interconnected Suspension.

It decouples the 4 modes of suspension movement (pitch, roll, bounce, and warp) and allows you to tune the 4 more independently. You can get stiff roll and pitch stiffness and soft bounce and warp stiffness.

You can combine it with electronically adjustable damping to get a pretty amazingly tuned and effective passive (read: immediate response and low energy demands) system.

A company out in western Australia called Kinetic came up with a version (H2 CES [CES are Ohlins' electronically adjustable damping elements]) that they showed off on several different typies of vehicle, then they were bought by Tenneco. McLaren uses a similar system (possibly Tenneco/Kinetic-sourced or co-developed but I never found confirmation of that).

HIS is the holy grail of decoupling suspension motion but there are similar system that use hydraulically decoupling rollbars. Versions of it have show up in Toyota and Lexus SUVs, Citroen used it to great success in the Xsara WRC cars, and I think Land Rover (and probably many others) have used it.

(video below is one of Kinetic's promo videos)

 

[Jalisurr]

if you want to get crazy with theoretical anti-roll design, what about long travel magnetic-ride controlled shocks? programming for such could be so that as speed increases it increases dampening to reduce body roll while still allowing significant articulation at lower speeds, or that as long as both sides are trying to travel in the same direction it decreases damping, but if they are attempting to travel opposite (one up, one down, i.e. roll) it tightens it up?

Don't the live valve shocks in the Raptors basically do this? They are a moving needle valve rather than magnetorheological, but they are able to change damping in response to pitch, roll, g-forces, steering angle, and suspension position. I think in 'rock crawl' mode it also generally softens them up a lot, and in sport or baja they are stiffer.

of course, while we are at it, we could look at combining air ride to change spring rate, or go with magnetic springs as well, or using springs contained in a jackscrew so that we can adjust preload on the spring during the drive. getting that to change quickly without causing significant issues may be problematic however. I think that air ride or magnetic springs (in addition to magnetic shocks) would be the best route for a high tech jack of all trades and master of all as well 4x4 setup.

Active springs would be pretty cool, but I'm not sure that the handling benefits would end up being that much over a good progressive or multi-stage spring (soft initial spring rate then stiffer the farther it travels)

 

[JimmyDean]

What you're looking for is called a Hydraulically Interconnected Suspension.

It decouples the 4 modes of suspension movement (pitch, roll, bounce, and warp) and allows you to tune the 4 more independently. You can get stiff roll and pitch stiffness and soft bounce and warp stiffness.

You can combine it with electronically adjustable damping to get a pretty amazingly tuned and effective passive (read: immediate response and low energy demands) system.

A company out in western Australia called Kinetic came up with a version (H2 CES [CES are Ohlins' electronically adjustable damping elements]) that they showed off on several different typies of vehicle, then they were bought by Tenneco. McLaren uses a similar system (possibly Tenneco/Kinetic-sourced or co-developed but I never found confirmation of that).

HIS is the holy grail of decoupling suspension motion but there are similar system that use hydraulically decoupling rollbars. Versions of it have show up in Toyota and Lexus SUVs, Citroen used it to great success in the Xsara WRC cars, and I think Land Rover (and probably many others) have used it.

(video below is one of Kinetic's promo videos)

kinda figured I wasn't the first person to consider something like this, figured there was something already out there. I'll have to look into this more.

 

[JimmyDean]

Don't the live valve shocks in the Raptors basically do this? They are a moving needle valve rather than magnetorheological, but they are able to change damping in response to pitch, roll, g-forces, steering angle, and suspension position. I think in 'rock crawl' mode it also generally softens them up a lot, and in sport or baja they are stiffer.


Active springs would be pretty cool, but I'm not sure that the handling benefits would end up being that much over a good progressive or multi-stage spring (soft initial spring rate then stiffer the farther it travels)

I think the only reason to have active springs would be to go from high speed to crawling without having to replace parts, or make compromises on one/both sections.

 

[BAUS67]

Shouldn't be any chairs happening in this thread, those are for when the discussion spills out into...everywhere else...

I would hesitate to say that solid is always stronger (plenty of weak solid axles out there), but I certainly agree that it's easier to make a strong solid axle than a strong independent suspension design. In the rear the handling tradeoff isn't enough to be worth changing to independent for most trucks or SUVs, in the front it is.

I also won't contest it's easier/cheaper to modify a solid axle...IF the modifications we're talking about are lifting it and putting on big tires. However if we're talking about modifying it to go fast over bumps...gonna be much easier if you started with independent and can just swap coilovers and control arms.

Again, I've never said that those who want big tires, going slow over rocks or through mud are wrong for wanting solid axles. It's just not what interests me in an off-road SUV and the point that I will always argue is the notion that the Bronco needs to have a SFA to be successful.

Sorry Jalisurr I was not trying to call you out, more specifically the comment of tradeoff between ride and strength, I see it a lot in there not just from you. Please don't take it as an attack on you.

I see it differently, …….. I feel the Bronco should have at least an option for SFA because they are always saying this is not just another SUV it is going after Wrangler's piece of the pie Its an off-roader. So it should have a low cost. high strength option for the guy that wants that. Then the mainstream getting what it wants a nice ride, they don't need a locker. OR ...…...… they build a compromise between ride and strength so why not compromise some towing for a better ride. I bought my TJ because it was an off-roader not because it had a nice ride. Only time will tell if Ford can pull it off, but here again other things can make up for losses in certain areas.

the chair thing is just a joke that is why I only talk about it here.

 

[frinesi2]

Sorry Jalisurr I was not trying to call you out, more specifically the comment of tradeoff between ride and strength, I see it a lot in there not just from you. Please don't take it as an attack on you.

I see it differently, …….. I feel the Bronco should have at least an option for SFA because they are always saying this is not just another SUV it is going after Wrangler's piece of the pie Its an off-roader. So it should have a low cost. high strength option for the guy that wants that. Then the mainstream getting what it wants a nice ride, they don't need a locker. OR ...…...… they build a compromise between ride and strength so why not compromise some towing for a better ride. I bought my TJ because it was an off-roader not because it had a nice ride. Only time will tell if Ford can pull it off, but here again other things can make up for losses in certain areas.

the chair thing is just a joke that is why I only talk about it here.

In an idea world, I agree that they should make an SFA Bronco to directly target Jeep, but I don't see Ford leadership EVER being that bold. Then again, they're constantly talking about the Bronco "family" so if the people on the inside trying to make it happen can push it out the door before the company goes through another big shakeup and cancels everything cool, maybe we'll get one after all. I expect very little from any manufacturer these days.

 

[jimbo92]

Solid axle and ride good eh? Toyota had that covered in the 90s.

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