The IFS vs SFA Thread

[Fosters]

The Raptor and Tremor package offer this... Do YOU know anything???

Both absolutely iconic brilliant rock crawlers. And a stellar reliability track record, shit's practically as indestructible as a nine inch spool.

And yes, we definitely need one more IFS equipped vehicles on the market. Because mall crawling is an underserved market.

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[Fosters]

Every Raptor I’ve looked at has been ordered with the 802A package which includes the Torsen. Dealers have limited allocation so they tend to get every option in order to maximize profit.

I haven't looked at them lately, did when they first came out, went and got a Rubicon instead.... which is the same exact thing that'll happen if the Bronco has an IFS. Guess things changed.

 

[bbostic5]

You will never see a limited slip offered from the factory in the front.

Both absolutely iconic brilliant rock crawlers. And a stellar reliability track record, shit's practically as indestructible as a nine inch spool.

And yes, we definitely need one more IFS equipped vehicles on the market. Because mall crawling is an underserved market.

Look at what you said. The Raptor and Tremor are off-road vehicles sold by Ford that come equipped with torsen fronts. And they do quite well off-road.

 

[Jalisurr]

Any limited slip will require torque difference between the wheels to function.

Not strictly true. Torsen and Clutch-Type limited slip diffs do require a torque difference. Viscous limited slip diffs require a speed difference.

In a limited traction low speed situation you will be at a disadvantage as power is going to both wheels. Yes, in a rally situation when you're trying to push as much snow, it's a whole different issue.

Power going to more driven wheels is almost never a disadvantage, except possibly for an inexperienced driver or one with poor throttle control (for them, yes, it may be the difference between not moving at all with an open diff and spinning with a LSD/locker). That's why locking or limited slip differentials are a desirable trait, and even more broadly why 4WD is desirable.

Have you ever driven a rwd vehicle with an open diff in the rear vs a limited slip? You will spin out way quicker in the one with a limited slip in a corner for the exact same reason.

Yes. Yes I have. I've autocrossed and road raced an MR2, E30 BMW, Camaro, Chevy S10 (it was silly) and two different Corvettes with various forms of rear differential (and driven them on the street as well).

With an open diff, yes, it's harder to spin out under power because you have no traction and are just spinning the inside tire in a corner. It's slow, and then at some point if you go faster you also lose traction on the outside tire and then it spins in an unpredictable manner.

With a Torsen diff, the inside will still spin but torque gets multiplied across to the outside tire and drives you around the corner significantly faster. It's no more likely to spin than an open diff and you have more control when it does as you can smoothly approach the torque limit.

With a clutch type diff, yes, the outside tire will spin more easily than with the above two. However, the way it approaches that limit is much more predicable and smooth. You can do a gentle controlled slide rather than spinning the inside tire and then suddenly spinning the car.

I've never spent much time in a car with a full spool/welded diff on pavement...basically only drifters do that because yeah, you're gonna slide everywhere.

When there is close to zero traction, the torque differential needed for that limited slip to do its job, will be greater. If it's really loose then you won't really get that limited slip action when more traction is needed.

Again not strictly true. In a Torsen diff, yeah, close to zero traction on one wheel means only a small amount transferred to the other wheel. Still better than an open diff where ALL your power goes to the one with no traction. With a clutch type even at zero traction on one side both wheels can get 50% of the torque.

You're acting as if you're insured 100% traction 100% of the time with a torsen. Why do subarus and mitsubishis resort to brake controlled traction control if those diffs are so awesome?

I don't think I ever claimed Torsen would give you 100% traction all the time. You can slide anything if you try hard enough. But a Torsen diff will absolutely give you better traction and control than an open one.

Brake based traction/stability control is used to help when you get past the limit of what your car can mechanically provide, the diff it has will just change where that limit may be. And if you're an experienced driver wanting to make good progress in snowy/icy conditions, you'll turn it off anyways. Controlled sliding is better than not moving.

 

[Fosters]

Not strictly true. Torsen and Clutch-Type limited slip diffs do require a torque difference. Viscous limited slip diffs require a speed difference.

And we're talking about torsens in the snow here, so my point stands.

Power going to more driven wheels is almost never a disadvantage, except possibly for an inexperienced driver or one with poor throttle control (for them, yes, it may be the difference between not moving at all with an open diff and spinning with a LSD/locker). That's why locking or limited slip differentials are a desirable trait, and even more broadly why 4WD is desirable.

Once again, in low traction situations you want to be in control more than anything. A spool is damn near gonna guarantee you wiping out every corner in the snow.

Yes. Yes I have. I've autocrossed and road raced an MR2, E30 BMW, Camaro, Chevy S10 (it was silly) and two different Corvettes with various forms of rear differential (and driven them on the street as well).

We're talking low traction situations where you'd use 4x4 - such as driving in the snow/ice/black ice/etc. Not autocross on 100 treadwear tires. That has nothing to do with a freaking bronco.

With an open diff, yes, it's harder to spin out under power because you have no traction and are just spinning the inside tire in a corner. It's slow, and then at some point if you go faster you also lose traction on the outside tire and then it spins in an unpredictable manner.

Take this concept and apply it below:

With a Torsen diff, the inside will still spin but torque gets multiplied across to the outside tire and drives you around the corner significantly faster. It's no more likely to spin than an open diff and you have more control when it does as you can smoothly approach the torque limit.

With a torsen you've got a bit of power going to both. When you're turning on ice you still need to turn the outside tire faster than the inside. With a torsen - the torque differential that's needed to actually trigger the torque multiplication and other stuff you're bringing up, will likely be more than enough to make sure one of your wheels is spinning - as the wheels will be turning at the same rate, again, in a corner, where they need to be turning at different rates.

With a clutch type diff, yes, the outside tire will spin more easily than with the above two. However, the way it approaches that limit is much more predicable and smooth. You can do a gentle controlled slide rather than spinning the inside tire and then suddenly spinning the car.

I've never spent much time in a car with a full spool/welded diff on pavement...basically only drifters do that because yeah, you're gonna slide everywhere.

I've had spooled mustangs, lockers in 4x4 rigs, limited slips and everything in between. There's no much more predictable and smooth in a limited slip. Ford's 8.8 limited slip requires 250 ft lbs of wheel torque difference (don't confuse that with power from the engine, we're talking strictly friction difference between the two wheels) for the clutches to allow slip. That's in a new/properly functioning LSD. As the clutches wear out you will turn it into more of an open diff - my 210k mile 8.8 I can overcome that friction with ease - and/or you can rebuild them with an extra clutch for a higher torque difference before slip is allowed - something a lot of drag racers and offroaders do for extra traction. Makes the LSD much stiffer..

The issue is though, even at 250 ft lbs difference between the wheels, you just don't have that kind of grip on ice. In a slippery situation, your wheels, with a limited slip, are gonna act as if they are locked together. Just like a spool. And in a corner, once again, they need to be turning at different rates.

Again not strictly true. In a Torsen diff, yeah, close to zero traction on one wheel means only a small amount transferred to the other wheel. Still better than an open diff where ALL your power goes to the one with no traction. With a clutch type even at zero traction on one side both wheels can get 50% of the torque.


I don't think I ever claimed Torsen would give you 100% traction all the time. You can slide anything if you try hard enough. But a Torsen diff will absolutely give you better traction and control than an open one.

I have a feeling we're talking about different things. I'm talking about control at low speeds in slippery situations, and control around corners not necessarily under power, you're talking about hauling ass. Yes, once you're in the ditch you'll want traction going to all wheels to get out... but an open diff will be more stable than any kind of limited slip that requires a torque difference between the wheels to start working. The ideal solution is the electronic lockers that are open diff when unlocked. Limited slips are a halfass solution between the two (locker and open diffs), one that usually wears out and is nowhere near as bullet proof.

Take a truck with a locker that's open when unlocked around a normal corner when it's snowy/icy outside. In order to see what I'm talking about, as an example, mash the gas fully. In the open diff, you'll boil the inside tire - sending no power to the outside which is gonna keep traction and keep you from sliding - and the vehicle will continue to coast where the front wheels are taking it. With the locker on - or a limited slip that requires any significant amount of torque difference between the wheels to allow for actual slip - you'll send power to both rear wheels and oversteer/spin out.

Yes, an experienced driver would countersteer, power out and go tokyo drift around there, but we're not talking about those

Brake based traction/stability control is used to help when you get past the limit of what your car can mechanically provide, the diff it has will just change where that limit may be. And if you're an experienced driver wanting to make good progress in snowy/icy conditions, you'll turn it off anyways. Controlled sliding is better than not moving.

They have to market these vehicles to people driving on the street as well.. the bulk is gonna be bought by soccer moms - like the 4 door wrangler.

 

[Jalisurr]

Once again, in low traction situations you want to be in control more than anything. A spool is damn near gonna guarantee you wiping out every corner in the snow.

I agree with you there. A spool is bad in the snow or whenever you aren't going straight and don't want to slide. I think we've got some misunderstanding on other points below.

We're talking low traction situations where you'd use 4x4 - such as driving in the snow/ice/black ice/etc. Not autocross on 100 treadwear tires. That has nothing to do with a freaking bronco.

Yep, fair. You mentioned RWD cars with limited slip diffs, my only experience with such vehicles is in high performance scenarios, going slow on the street the diff is never going to do anything, and I generally only drive AWD or 4WD in the snow.

With a torsen you've got a bit of power going to both. When you're turning on ice you still need to turn the outside tire faster than the inside. With a torsen - the torque differential that's needed to actually trigger the torque multiplication and other stuff you're bringing up, will likely be more than enough to make sure one of your wheels is spinning - as the wheels will be turning at the same rate, again, in a corner, where they need to be turning at different rates.

I've had spooled mustangs, lockers in 4x4 rigs, limited slips and everything in between. There's no much more predictable and smooth in a limited slip. Ford's 8.8 limited slip requires 250 ft lbs of wheel torque difference (don't confuse that with power from the engine, we're talking strictly friction difference between the two wheels) for the clutches to allow slip. That's in a new/properly functioning LSD. As the clutches wear out you will turn it into more of an open diff - my 210k mile 8.8 I can overcome that friction with ease - and/or you can rebuild them with an extra clutch for a higher torque difference before slip is allowed - something a lot of drag racers and offroaders do for extra traction. Makes the LSD much stiffer..

The issue is though, even at 250 ft lbs difference between the wheels, you just don't have that kind of grip on ice. In a slippery situation, your wheels, with a limited slip, are gonna act as if they are locked together. Just like a spool. And in a corner, once again, they need to be turning at different rates.

I think I understand where the misunderstanding is now. It sounds like you're talking about a more traditional LSD with preload - where it requires a certain amount of force to allow slip. Torsen diffs have no preload like other types. You can freely turn one wheel when not under power, in fact it only starts to lock up when there IS a torque difference between the wheels, otherwise it acts as if it's an open diff. There's no wheel torque difference required to allow slip.

ETA: I sort of understand your point about an open diff being more stable, but it's also more likely to just not go anywhere. Torsen diffs are a very forgiving way to get extra traction without the 'locked up' effect in turns you are talking about.

I'll also point out Humvees used Torsen diffs front and rear, so they must be worth something even outside of rally cars

EDIT2:
Just to use someone else's words where I may be failing to explain, I pulled this out of the wikipedia page about LSDs, talking about geared, torque sensing diffs (aka torsen):

Unlike other friction-based LSD designs that combine a common spider gear "open" differential in combination with friction materials that inhibit differentiation, the torque sensing design is a unique type of differential, with torque bias inherent in its design, not as an add-on. Torque bias is only applied when needed, and does not inhibit differentiation. The result is a true differential that does not bind up like LSD and locking types, but still gives increased power delivery under many road conditions.

 

[OX1]

You will never see a limited slip offered from the factory in the front. A locker that's open when unlocked - like the rubicon - yes, but a limited slip will not happen. If you knew anything about offroading you'd know why that's a bad idea... Not to mention all of the negative side effects it would have on the street.

Not sure on the full context of your statement here, but you could get a factory Power Loc front LS, in 78.

Any limited slip will require torque difference between the wheels to function. In a limited traction low speed situation you will be at a disadvantage as power is going to both wheels. Yes, in a rally situation when you're trying to push as much snow, it's a whole different issue.

Have you ever driven a rwd vehicle with an open diff in the rear vs a limited slip? You will spin out way quicker in the one with a limited slip in a corner for the exact same reason. When there is close to zero traction, the torque differential needed for that limited slip to do its job, will be greater. If it's really loose then you won't really get that limited slip action when more traction is needed.

You're acting as if you're insured 100% traction 100% of the time with a torsen. Why do subarus and mitsubishis resort to brake controlled traction control if those diffs are so awesome?

Not the Wavetrac

http://www.wavetrac.net/technical.htm

I have one in the front of my EVO8, and it works on high speed rumble strips, even if one tire is in the air.
Not sure how durable it would be with say a 35"-37" tire, but as an example, they do make a 35 spline 9" version.

.https://www.moserengineering.com/9-ford-35-spline-wavetrac.item

I'd still prefer ARB type diffs, or better yet mechanically locked diffs like the OX.
But I have been somewhat impressed by open diff's and brake locking to create
a temp sort of LS. Some of those seem to work well, but again I wouldn't want
them in hard core crawling.

 

[Cybrrstarr]

Back on the subject.........


IFS sucks. Lol

 

[Nanook]

Back on the subject.........


IFS sucks. Lol

And the majority is happy with a turbo 4cyl 4Runner that you might be able to remove a roof panel on.

 

[TeocaliMG]

The torsen option take rate is very tiny... and just like a torsen would do when used in drag racing, it would get demolished for rock crawling. It's also a terrible idea driving around in the snow for example... you're pretty much guaranteed one of your front wheels will lose traction in a turn.


Yes, 5. 10" of wheel travel is a joke for rock crawling. You're not doing this in a stock rig.

This thread isn't too long yet to got back and see what I wrote about wheel travel vs articulation. You can't drive on a 20" rock and call it 20" of wheel travel. The most obvious point is that the CG of the Jeep has moved, so you are soiling the measurement with "Jeep travel" For example a Tractor with exactly zero wheel travel could do this maneuver by virtue of a pivoting front axle. The Wrangler does however actually have decent wheel travel, just not in Jounce. Any amount of wheel travel will aid in articulation, but you CAN have articulation which is at least partially independent from wheel travel, like down travel of a single wheel, this is an inherent advantage of SFA.

As long as we are talking stock or lightly modified in the range of 10-15" of REAL wheel travel, an IFS/SRA will perform surprisingly well. Looking at the Bronco R, it is clear that a stock Bronco wont have 14"+ but likely something closer to 10, and considering the ZR2 is a half decent off-roader with only 8" I think I am ok with that. If you only care about rocks and think that is the sole key to success then this trade off (though more nuanced than you might think) is not worth it for you. I personally like jounce travel at least as much as rebound if not more for my style of off-roading, and I am open to the idea that Bronco can meet or beat Jeep in basically every other facet discussed while being SIGNIFICANTLY more competitive in the rocks than any other "Wrangler competitor" before it.

Edit: Oh man, just kept reading more of the latest threads. Sheesh, between the "IFS sucks" and "like we need more IFS rigs" I am worried that some of you can't read. At least the OG IFS critics I have had back and forth with could maintain debate format. I think for my own sanity I am going to take a break from this and/or only engage in proper technical discussion, its been... fun...

 

[Nanook]

This thread isn't too long yet to got back and see what I wrote about wheel travel vs articulation. You can't drive on a 20" rock and call it 20" of wheel travel. The most obvious point is that the CG of the Jeep has moved, so you are soiling the measurement with "Jeep travel" For example a Tractor with exactly zero wheel travel could do this maneuver by virtue of a pivoting front axle. The Wrangler does however actually have decent wheel travel, just not in Jounce. Any amount of wheel travel will aid in articulation, but you CAN have articulation which is at least partially independent from wheel travel, like down travel of a single wheel, this is an inherent advantage of SFA.

As long as we are talking stock or lightly modified in the range of 10-15" of REAL wheel travel, an IFS/SRA will perform surprisingly well. Looking at the Bronco R, it is clear that a stock Bronco wont have 14"+ but likely something closer to 10, and considering the ZR2 is a half decent off-roader with only 8" I think I am ok with that. If you only care about rocks and think that is the sole key to success then this trade off (though more nuanced than you might think) is not worth it for you. I personally like jounce travel at least as much as rebound if not more for my style of off-roading, and I am open to the idea that Bronco can meet or beat Jeep in basically every other facet discussed while being SIGNIFICANTLY more competitive in the rocks than any other "Wrangler competitor" before it.

Edit: Oh man, just kept reading more of the latest threads. Sheesh, between the "IFS sucks" and "like we need more IFS rigs" I am worried that some of you can't read. At least the OG IFS critics I have had back and forth with could maintain debate format. I think for my own sanity I am going to take a break from this and/or only engage in proper technical discussion, its been... fun...

You have done a great job defending IFS.
We have agreement that the Bronco’s stock rock crawling capabilities might and should be greater than every other IFS suv (H1 excluded) that’s been built. We won’t know that for sure for quite awhile. Safe to say we all hope that is true.
But this thread is kind of a moot point because there’s also agreement that IFS presents greater limitations and greater expense for customers that want to modify their vehicle beyond a leveling kit.
it seems there’s also agreement that the aftermarket will be the key to the broncos success for image and profits and it’s safe to assume that everyone has had an image in mind of what their new Bronco would look like after customization and some are disappointed about the inevitable tire size limitations and it seems others are ignoring it.
What looks cooler slightly modified?
FJ on 33’s
Wrangler on 37’s

Cut the fenders all you want to put 37’s on the FJ and you’re going to break things.

 

[PNW_Bronco94]

And we're talking about torsens in the snow here, so my point stands.

 

[phillyfx4]

Back on the subject.........


IFS sucks. Lol

not for me it won't …..state of the art IFS(for 2021 anyway) on a 4 door Raptor Bronco …..I'm going surf fishing and getting thru the NE snowfalls in style

you maniac's can rock crawl to your hearts desire.....ENJOY

 

[Nanook]

not for me it won't …..state of the art IFS(for 2021 anyway) on a 4 door Raptor Bronco …..I'm going surf fishing and getting thru the NE snowfalls in style

you maniac's can rock crawl to your hearts desire.....ENJOY

For this purpose, other than brand loyalty, why have you been waiting and anticipating the new bronco? You have had many options for many years.

 

[BroncoMike]

For this purpose, other than brand loyalty, why have you been waiting and anticipating the new bronco? You have had many options for many years.

He said "in style".

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