4 Hi Auto on my wife’s 4Xe Sahara is amazing in the snow

[Mikester86]

Just have to say that 4 Hi Auto on my wife’s 4Xe Sahara is amazing in the snow and I wish my Rubicon had it. That is all.

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[dcmdon]

Yes it is. For $500, I'm amazed that everyone doesn't get it. It's even great in heavy rain.

I put it on at the first sign of precipitation and don't disengage it until the roads are dry. Typically several days later. It's designed to be left on 100% of the time. In my head I disengage it to imperceptibly improve fuel economy. Though I don't see it in instantaneous mileage readouts.

I've got SelecTrac and 4 Nokian 35' snows on my Gladiator and it's a beast in the snow.

 

[AFD]

Had my first winter drives in 4-auto today and it actually made it around pretty good without any issues.

The rural roads were a mixed mess with only the center partially cleared (driver's side tire tracks), but glazed and icy with sand thrown down, while the rest was thick frozen, crunchy snow a few inches thick with fresh powdery snow blown on top. Had a few times where it wanted to pull further into the softer snow near the berm, which I've had happen with standing water in heavy rain, but fortunately, didn't do any unintentional off-roading.

City roads were a different kind of mess, which were cleared and then re-treated with their usual slimy brine or beat juice formula, new fresh snow, lots of icy/glazy spots and then some skid added on top to make it a bit slushy. Felt slippery as hell, but even creeping up the steeper hills, it didn't have any problems.

Still felt a lot different than driving an AWD vehicle (which I know is a bit different), but everything seemed fairly seamless and predictable. No LSD on mine and not really sure exactly how much was the 4WD-auto switching, the BLD if any and just plain traction control, but it all worked pretty well imo and handled cornering much better than when I only had 4HI in my old Cherokee.

 

[jeepoch]

Mike,

I'm jealous. The SelecTrac is pretty amazing.

But don't underestimate the other features that help contribute to our JL's amazing traction prowess. Both the Brake Lock Differential (BLD) and Traction Control (TC) systems are amazing in their own right.

I have a 2019 Sport, 3.6L Auto, lifted on 35s with open diffs, no LSD and certainly no 4-auto. But with a little patience and disciplined throttle control, one can get pretty similar results. Granted the SelectTrac really makes it much easier, but knowing how your JL (independent of trim) powertrain works gives you quite an advantage over nearly every other vehicle on the road today.

Both the BLD and TC come standard on every JL. These are software features implemented via the Automated Braking System (ABS). The BLD is always active, no matter the transfer case setting. TC on the other hand is only available in 2 or 4Hi. It is automatically disabled in 4Lo.

The primary difference between the two is that Traction Control is BLD on steroids. BLD works basically on each wheel, whereas TC works on all four wheels in concert. They both try to achieve the same purpose though; improve overall traction by reducing wheel 'slip'.

BLD works independently by sensing the rotational wheel speed of each wheel on a single axle. When one wheel spins faster (the slipping wheel), the ABS software detects this and applies automatic braking to just the slipping wheel. This naturally allows more torque to be applied to the other non-slipping wheel.

Recall, with pure open diffs, torque is applied evenly to each wheel as long as they are both rotating at the same rate. However as one spins faster, such as going through a turn, the outside wheel (the one spinning faster) gets most (nearly all) of the torque. This is by design and why open diffs are preferred in the first place. They allow smooth and efficient power when cornering.

The disadvantage of open diffs are that they are nearly useless in low traction situations. Since the wheel which spins faster (the one slipping), it gets nearly all the applied torque. Thus, little to no energy is actually applied to the 'gripping' wheel.

Hence the introduction of 4wd. You now have the other axle, hopefully still applying torque evenly to both of it's wheels. As long as it is, motive force is maintained. If not, then one wheel on each axle is slipping, momentum is now lost because all available torque is applied to the faster, slipping (non-gripping) wheels.

Hence the introduction of locking axles. With a 'locked' axle, each wheel spins at the exact same rate and torque is applied evenly to both wheels all the time independent of traction. With two locked axles, it only requires just one gripping wheel to maintain motive effort. Just one. Compare that to a non-locked (open-diff) system which requires a minimum of at least two gripping wheels (on the same axle) to maintain motive effort.

However, a locked axle does not corner well. Since the outside wheel naturally rotates faster, due to a larger radius of travel as compared to the inner wheel, the two wheels must rotate at different speeds. But because they can't (they are mechanically locked), then something's got to give. Hopefully that's tire skid and not the shaving of gears. So it's never a good idea to drive around for any extended period of time with a locked axle.

Auto 4WD does nothing to change the physics of any of that. However, what it does (extremely well) is that it senses wheel slip on any wheel and auto-magically engages power to both axles in order to allow the other two wheels, on the other axle, to possibly 'help' provide potential motive effort. Hence the name Part-Time 4WD or even 'All Wheel Drive' (AWD). The only difference is whether this functionality can be manually selected. PT-4WD it can, AWD it cannot. With AWD, 4-auto is always active.

So you can (in theory) still do this all manually without a SelectTrac transfer case. In reality however the sensing of any wheel slip by the driver (directly) is a pretty difficult thing to do. That's the true advantage of SelectTrac.

Additionally, what makes 4WD so much better than AWD is basically off-road (or any severe condition) in which you want to override this potential, even if part-time, dual axle selection. Any time you want to exclusively engage power to both axles, full-time, under your direct control is what makes 4WD way better than AWD.

Also notice that 4-auto has, no, (not even indirect), control over the engagement of lockers. It can automatically apply power to either just one axle or two depending on just the detection of wheel slip only.

With lockers engaged (manually), 4-auto becomes essentially useless because there will be no wheel slip. Both wheels will rotate mechanically at the same rate. You could still play games by locking just the rear axle only, thus allowing potential wheel slip on the front, thereby allowing the SelectTrac transfer case to still allow either 2wd (one axle) or 4wd (two axles) to be powered automatically. Some may argue that's what makes the Limited Slip Differential (LSD) more attractive. It can, even partially, lock up it's axle automatically.

Lastly, to wind up this diatribe, Traction Control works in concert with BLD to try and keep your vehicle going straight by monitoring any wheel slip and automatically applying braking action comprehensively, over any (or all) of the four wheels to help ensure that the currently applied torque does not cause additional wheel slip. Without any additional slippage, the vehicle's current motive effort should still be forward, not sideways.

So armed with more knowledge, you should better be able to understand exactly how and why SelectTrac makes your JL even more capable. But even without it, using your powertrain appropriately, you should be able to manage just about any condition you come across.

For me, living in Northern Colorado I find myself in slippery situations all the time. I routinely find that I rely on both the BLD and TC systems to get or keep me out of trouble. In deep snow, I do prefer 4Lo especially in any type of steep grade. However, without lockers I really need to be more cognitive of throttle discipline. I need just the proper amount of torque, but no more, in order to prevent wheel slip. In many situations when I do get stuck, simply putting it back into 4Hi allows the BLD and TC systems to work their magic. This typically then gives me just that extra little amount of power to a better gripping wheel. Having a SelectTrac transfer case would certainly make this a whole lot easier.

But then again, where's the fun in that?
Regardless, these JL's are fribben awesome.

Hope this helps.
Merry Christmas to you and yours.
Jay

 

[Dyolfknip74]

Mike,

I'm jealous. The SelecTrac is pretty amazing.

But don't underestimate the other features that help contribute to our JL's amazing traction prowess. Both the Brake Lock Differential (BLD) and Traction Control (TC) systems are amazing in their own right.

I have a 2019 Sport, 3.6L Auto, lifted on 35s with open diffs, no LSD and certainly no 4-auto. But with a little patience and disciplined throttle control, one can get pretty similar results. Granted the SelectTrac really makes it much easier, but knowing how your JL (independent of trim) powertrain works gives you quite an advantage over nearly every other vehicle on the road today.

Both the BLD and TC come standard on every JL. These are software features implemented via the Automated Braking System (ABS). The BLD is always active, no matter the transfer case setting. TC on the other hand is only available in 2 or 4Hi. It is automatically disabled in 4Lo.

The primary difference between the two is that Traction Control is BLD on steroids. BLD works basically on each wheel, whereas TC works on all four wheels in concert. They both try to achieve the same purpose though; improve overall traction by reducing wheel 'slip'.

BLD works independently by sensing the rotational wheel speed of each wheel on a single axle. When one wheel spins faster (the slipping wheel), the ABS software detects this and applies automatic braking to just the slipping wheel. This naturally allows more torque to be applied to the other non-slipping wheel.

Recall, with pure open diffs, torque is applied evenly to each wheel as long as they are both rotating at the same rate. However as one spins faster, such as going through a turn, the outside wheel (the one spinning faster) gets most (nearly all) of the torque. This is by design and why open diffs are preferred in the first place. They allow smooth and efficient power when cornering.

The disadvantage of open diffs are that they are nearly useless in low traction situations. Since the wheel which spins faster (the one slipping), it gets nearly all the applied torque. Thus, little to no energy is actually applied to the 'gripping' wheel.

Hence the introduction of 4wd. You now have the other axle, hopefully still applying torque evenly to both of it's wheels. As long as it is, motive force is maintained. If not, then one wheel on each axle is slipping, momentum is now lost because all available torque is applied to the faster, slipping (non-gripping) wheels.

Hence the introduction of locking axles. With a 'locked' axle, each wheel spins at the exact same rate and torque is applied evenly to both wheels all the time independent of traction. With two locked axles, it only requires just one gripping wheel to maintain motive effort. Just one. Compare that to a non-locked (open-diff) system which requires a minimum of at least two gripping wheels (on the same axle) to maintain motive effort.

However, a locked axle does not corner well. Since the outside wheel naturally rotates faster, due to a larger radius of travel as compared to the inner wheel, the two wheels must rotate at different speeds. But because they can't (they are mechanically locked), then something's got to give. Hopefully that's tire skid and not the shaving of gears. So it's never a good idea to drive around for any extended period of time with a locked axle.

Auto 4WD does nothing to change the physics of any of that. However, what it does (extremely well) is that it senses wheel slip on any wheel and auto-magically engages power to both axles in order to allow the other two wheels, on the other axle, to possibly 'help' provide potential motive effort. Hence the name Part-Time 4WD or even 'All Wheel Drive' (AWD). The only difference is whether this functionality can be manually selected. PT-4WD it can, AWD it cannot. With AWD, 4-auto is always active.

So you can (in theory) still do this all manually without a SelectTrac transfer case. In reality however the sensing of any wheel slip by the driver (directly) is a pretty difficult thing to do. That's the true advantage of SelectTrac.

Additionally, what makes 4WD so much better than AWD is basically off-road (or any severe condition) in which you want to override this potential, even if part-time, dual axle selection. Any time you want to exclusively engage power to both axles, full-time, under your direct control is what makes 4WD way better than AWD.

Also notice that 4-auto has, no, (not even indirect), control over the engagement of lockers. It can automatically apply power to either just one axle or two depending on just the detection of wheel slip only.

With lockers engaged (manually), 4-auto becomes essentially useless because there will be no wheel slip. Both wheels will rotate mechanically at the same rate. You could still play games by locking just the rear axle only, thus allowing potential wheel slip on the front, thereby allowing the SelectTrac transfer case to still allow either 2wd (one axle) or 4wd (two axles) to be powered automatically. Some may argue that's what makes the Limited Slip Differential (LSD) more attractive. It can, even partially, lock up it's axle automatically.

Lastly, to wind up this diatribe, Traction Control works in concert with BLD to try and keep your vehicle going straight by monitoring any wheel slip and automatically applying braking action comprehensively, over any (or all) of the four wheels to help ensure that the currently applied torque does not cause additional wheel slip. Without any additional slippage, the vehicle's current motive effort should still be forward, not sideways.

So armed with more knowledge, you should better be able to understand exactly how and why SelectTrac makes your JL even more capable. But even without it, using your powertrain appropriately, you should be able to manage just about any condition you come across.

For me, living in Northern Colorado I find myself in slippery situations all the time. I routinely find that I rely on both the BLD and TC systems to get or keep me out of trouble. In deep snow, I do prefer 4Lo especially in any type of steep grade. However, without lockers I really need to be more cognitive of throttle discipline. I need just the proper amount of torque, but no more, in order to prevent wheel slip. In many situations when I do get stuck, simply putting it back into 4Hi allows the BLD and TC systems to work their magic. This typically then gives me just that extra little amount of power to a better gripping wheel. Having a SelectTrac transfer case would certainly make this a whole lot easier.

But then again, where's the fun in that?
Regardless, these JL's are fribben awesome.

Hope this helps.
Merry Christmas to you and yours.
Jay

Great post man. Merry Xmas.

 

[Dan M.]

It sounds awesome. Although I'm kind of glad I don't have it. My wife is afraid to use my Jeep in the winter as she doesn't want to mess with engaging 4Hi. This is good for me as I worry if she starts to like my Jeep to much she will take it.

 

[Bzinsky]

Mike,

I'm jealous. The SelecTrac is pretty amazing.

But don't underestimate the other features that help contribute to our JL's amazing traction prowess. Both the Brake Lock Differential (BLD) and Traction Control (TC) systems are amazing in their own right.

I have a 2019 Sport, 3.6L Auto, lifted on 35s with open diffs, no LSD and certainly no 4-auto. But with a little patience and disciplined throttle control, one can get pretty similar results. Granted the SelectTrac really makes it much easier, but knowing how your JL (independent of trim) powertrain works gives you quite an advantage over nearly every other vehicle on the road today.

Both the BLD and TC come standard on every JL. These are software features implemented via the Automated Braking System (ABS). The BLD is always active, no matter the transfer case setting. TC on the other hand is only available in 2 or 4Hi. It is automatically disabled in 4Lo.

The primary difference between the two is that Traction Control is BLD on steroids. BLD works basically on each wheel, whereas TC works on all four wheels in concert. They both try to achieve the same purpose though; improve overall traction by reducing wheel 'slip'.

BLD works independently by sensing the rotational wheel speed of each wheel on a single axle. When one wheel spins faster (the slipping wheel), the ABS software detects this and applies automatic braking to just the slipping wheel. This naturally allows more torque to be applied to the other non-slipping wheel.

Recall, with pure open diffs, torque is applied evenly to each wheel as long as they are both rotating at the same rate. However as one spins faster, such as going through a turn, the outside wheel (the one spinning faster) gets most (nearly all) of the torque. This is by design and why open diffs are preferred in the first place. They allow smooth and efficient power when cornering.

The disadvantage of open diffs are that they are nearly useless in low traction situations. Since the wheel which spins faster (the one slipping), it gets nearly all the applied torque. Thus, little to no energy is actually applied to the 'gripping' wheel.

Hence the introduction of 4wd. You now have the other axle, hopefully still applying torque evenly to both of it's wheels. As long as it is, motive force is maintained. If not, then one wheel on each axle is slipping, momentum is now lost because all available torque is applied to the faster, slipping (non-gripping) wheels.

Hence the introduction of locking axles. With a 'locked' axle, each wheel spins at the exact same rate and torque is applied evenly to both wheels all the time independent of traction. With two locked axles, it only requires just one gripping wheel to maintain motive effort. Just one. Compare that to a non-locked (open-diff) system which requires a minimum of at least two gripping wheels (on the same axle) to maintain motive effort.

However, a locked axle does not corner well. Since the outside wheel naturally rotates faster, due to a larger radius of travel as compared to the inner wheel, the two wheels must rotate at different speeds. But because they can't (they are mechanically locked), then something's got to give. Hopefully that's tire skid and not the shaving of gears. So it's never a good idea to drive around for any extended period of time with a locked axle.

Auto 4WD does nothing to change the physics of any of that. However, what it does (extremely well) is that it senses wheel slip on any wheel and auto-magically engages power to both axles in order to allow the other two wheels, on the other axle, to possibly 'help' provide potential motive effort. Hence the name Part-Time 4WD or even 'All Wheel Drive' (AWD). The only difference is whether this functionality can be manually selected. PT-4WD it can, AWD it cannot. With AWD, 4-auto is always active.

So you can (in theory) still do this all manually without a SelectTrac transfer case. In reality however the sensing of any wheel slip by the driver (directly) is a pretty difficult thing to do. That's the true advantage of SelectTrac.

Additionally, what makes 4WD so much better than AWD is basically off-road (or any severe condition) in which you want to override this potential, even if part-time, dual axle selection. Any time you want to exclusively engage power to both axles, full-time, under your direct control is what makes 4WD way better than AWD.

Also notice that 4-auto has, no, (not even indirect), control over the engagement of lockers. It can automatically apply power to either just one axle or two depending on just the detection of wheel slip only.

With lockers engaged (manually), 4-auto becomes essentially useless because there will be no wheel slip. Both wheels will rotate mechanically at the same rate. You could still play games by locking just the rear axle only, thus allowing potential wheel slip on the front, thereby allowing the SelectTrac transfer case to still allow either 2wd (one axle) or 4wd (two axles) to be powered automatically. Some may argue that's what makes the Limited Slip Differential (LSD) more attractive. It can, even partially, lock up it's axle automatically.

Lastly, to wind up this diatribe, Traction Control works in concert with BLD to try and keep your vehicle going straight by monitoring any wheel slip and automatically applying braking action comprehensively, over any (or all) of the four wheels to help ensure that the currently applied torque does not cause additional wheel slip. Without any additional slippage, the vehicle's current motive effort should still be forward, not sideways.

So armed with more knowledge, you should better be able to understand exactly how and why SelectTrac makes your JL even more capable. But even without it, using your powertrain appropriately, you should be able to manage just about any condition you come across.

For me, living in Northern Colorado I find myself in slippery situations all the time. I routinely find that I rely on both the BLD and TC systems to get or keep me out of trouble. In deep snow, I do prefer 4Lo especially in any type of steep grade. However, without lockers I really need to be more cognitive of throttle discipline. I need just the proper amount of torque, but no more, in order to prevent wheel slip. In many situations when I do get stuck, simply putting it back into 4Hi allows the BLD and TC systems to work their magic. This typically then gives me just that extra little amount of power to a better gripping wheel. Having a SelectTrac transfer case would certainly make this a whole lot easier.

But then again, where's the fun in that?
Regardless, these JL's are fribben awesome.

Hope this helps.
Merry Christmas to you and yours.
Jay

Couple minor corrections

1)in our jeeps 4 auto is activated by throttle position AND wheel slip. On the street, the reason you don’t hear any wheel slip if you floor it, is because it was already activated by the throttle.

2)4auto only controls the percentage of power to the front axle. Our rear axle is permanently connected to the transfer case and that doesn’t change. There is no variable power to the rear. But obviously if you only control the front, then full clutch activation would be a 50/50 power split front and rear.

 

[dcmdon]

Still felt a lot different than driving an AWD vehicle (which I know is a bit different), but everything seemed fairly seamless and predictable. No LSD on mine and not really sure exactly how much was the 4WD-auto switching, the BLD if any and just plain traction control, but it all worked pretty well imo and handled cornering much better than when I only had 4HI in my old Cherokee.

That is probably because of the height / weight of the vehicle.

This is truly an AWD system in the same sense that the Haldex system on an Audi A3, A4 is.

We are talking about something without a true center differential, but rather a clutch pack that can lock anywhere between 0% and 100%.

At 0% its RWD (in the Audi's cases its FWD). At 100% the front and rear axles are locked together.

The Jeep system doesn't just lock. Even in the dry, if you are running something like AlfaOBD you can see the clutch pack engage as you give more and more throttle. This is pretty standard logic on AWD vehicles. Things like gear (which impacts the torque at the wheels) and steering angle (Less steering angle allows more engagement because less slip is required). Bottom line is that if you are accelerating hard away from a light in a straight line the front tires are being brought into play to a significant degree.

Our system and the Haldex system are different from some AWD systems that actually have a center differential. So they are always sending power to the secondary set of drive wheels. But in practical application they achieve the same thing and feel the same in all situations other than truly high performance driving.

Couple minor corrections

1)in our jeeps 4 auto is activated by throttle position AND wheel slip. On the street, the reason you don’t hear any wheel slip if you floor it, is because it was already activated by the throttle.

2)4auto only controls the percentage of power to the front axle. Our rear axle is permanently connected to the transfer case and that doesn’t change. There is no variable power to the rear. But obviously if you only control the front, then full clutch activation would be a 50/50 power split front and rear.

Yes, exactly, well said.

Some people seem to think that they will feel the wheel spin, then the system correct and engage. Not the case because the front wheels are engaged proactively as throttle increases.

 

[Mikester86]

Driving home last night turned onto our street while still in 4 Hi Auto and accelerated somewhat aggressively. The road is snow covered and loose with some sloppiness. It went well, then I dropped it into 4 WD part time and it definitely hooked up better.

But as a set it and forget it option, 4Hi Auto is fantastic and much simpler for my wife to deal with. It sure would be a great option on my Rubicon, but 4 Hi part time is no slouch. Just more to worry about when traveling and the roads continually change from dry to wet to snow covered to slush to icy and everywhere in between.

Thank you all for the replied and knowledge drops! Merry Christmas all and Happy New Year!

 

[dcmdon]

IMHO - your perception that it hooked up better was in your head.

I understand the desire to still have some benefit to 4H.

but I've wheeled in 4H auto just to see how it did and there was no perceptible difference.

 

[Valpo Jeep]

We had the 242 TC in our old Grand Cherokee which was like the auto in the JL. Had the full time quadratrack 4X4 in another GC and it was indeed awesome as well.

So far the command track is just OK to me with this snow storm

 

[mgarciaknight]

My 2006 Jeep Commander with the Full Time 4wd was a BEAST, seamless, and flawless.

 

[Bzinsky]

I understand the desire to still have some benefit to 4H.

Well not a traction benefit, if that’s what you meant.
4auto uses friction, so the downside is it can and will overheat. Just want to run in 4hi if you know for a fact you’ll be needing it for a little while, like driving through continuous snow/ice/mud/sand

 

[Mikester86]

IMHO - your perception that it hooked up better was in your head.

I understand the desire to still have some benefit to 4H.

but I've wheeled in 4H auto just to see how it did and there was no perceptible difference.

Not in my experience. 4 Hi part time traction was better. Traction at fast acceleration was immediate and the ass end stayed straight. My wife in the passenger seat even commented on it. It seamed to push and pull the Jeep with less effort and basically instant traction.

 

[dcmdon]

Well not a traction benefit, if that’s what you meant.
4auto uses friction, so the downside is it can and will overheat. Just want to run in 4hi if you know for a fact you’ll be needing it for a little while, like driving through continuous snow/ice/mud/sand

I asked my Jeep service writer if on Selectrac, there was an actual splined connection engaging the front axle when the transfer case was put in 4H, or if the clutch just engaged 100% all the time.

He told me that there is no splined connection, the clutch just engages fully and stays engaged.

Your worry about it overheating is unfounded. Like all AWD systems it is designed to function full time. In prolonged use on low tractions surfaces it will remain engaged. When fully engaged, no heat is generated.

Bottom line is that on the road and in most off road situations there is no need to engage 4H. Though most of us will just because it makes us feel better.

Not in my experience. 4 Hi part time traction was better. Traction at fast acceleration was immediate and the ass end stayed straight. My wife in the passenger seat even commented on it. It seamed to push and pull the Jeep with less effort and basically instant traction.

If that is what you felt, then I sure can't tell you that you are wrong.

But it is different from what I've experienced. It feels no different from the AWD cars I've owned in the past, with zero perceptible slippage before the secondary axle is engaged.

Like I mentioned before, even on dry roads, the front is gradually engaged as throttle is applied. Again, at least on the Gladiator, where a member on jeep gladiator.com shared AlfaOBD logs showing the clutch engaging.

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