I also use 2H on the highway, or at most 4A with vehicle in Normal(So power is moved off the front). Your handling will be much more predictable and closer what you are used to.
No 4H
- Thread starter Rob6805
- Start date
Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
This is good to know. I wasn't sure about that. I'll have to pay more attention. We currently have snowy weather here in Northern MI so I have lots of opportunity to check it out.
In general yes. However braking is enhanced with a 50/50 locked transfer case. Your stopping distance in 4 High is greatly reduced over 2WD in icey conditions as brake force is divided up between 4 wheels via the driveshafts vs an unlocked situation. IIHS has some good videos on it. Normally the front bears most of the load. In 4WD both axles share the brake force so if one axle has no traction but the other does, the axle with traction assists the axle without through the driveline. 4A doesn’t really do this. I notice my braking uses ABS much less when in 4H in those situations where I’m on hard packed snow or ice. You guys technically have 4H even pre 22, it’s just mud and ruts selection.
Last edited:
ROBERT BONNER
Full Access Members
Lots of good information and speculation in the preceding posts. I probably started a lot of it with my tongue in cheek post a few days ago. To be clear, I've driven my '20 FX4 MAX in a little bit of snow and ice and the wonder knob selections worked pretty good for snow. The mud and rut selection works really well for those conditions, I've had a lot more opportunities to use that so far than the snow mode. That being said a few clarifications of fact and another opinion or two:
According to my Ford buddies, both the transfer case (at least the 2 speed in my FX4) and the eLSD are, as mentioned above, "clutch" systems, the eLSD uses clutches acting on an actual geared differential, while the wet clutch system in the transfer case allows speed as well as torque "differentials" without actually containing a geared differential as many of you realized already.
However, when operating properly, both are designed to absolutely lock for a true 50/50 torque split and zero difference in velocity between the front and rear axles in the case of the transfer case and between the RH and LH rear axles in the eLSD's case. In the case of the eLSD, this can take place under certain conditions in certain knob modes as well as when the lock button is engaged. Similarly, the transfer case will completely lock the axles as well. Not surprisingly, high steering angles will "unlock" the transfer case and in certain modes the eLSD as well.
I'd still like the independent ability to "lock" the transfer case in high (4H). As many of us, I've driven a lot of vehicles in a lot of conditions (including a VW Polo, VW GTI, and Porsche 911 on the Nürburgring). Locking the "center differential" (hopefully gear diff aficionados will forgive the term) tends to keep the vehicle going in a straight line, resisting deflections from semi-frozen slush, etc. It also equalizes the braking force through all wheels allowing more braking force to be applied before and during ABS events. Finally, front wheels have less rolling resistance than undriven front wheels. Not knowing when some software programmer/tuner decided to disengage the "lock", or re engage it is what I find unsettling during certain higher performance situations.
Finally, the best 4x4 vehicle's I ever drove in the snow were 4x4 F150's of various vintages with manual transmissions and limited slip rear ends. The very best was an '86 F150. The 4x4 selector was shaped and positioned so that you could operate it with either your right foot or hand, moving from 2H to 4H and back instantly, no engagement lag. The engine braking and control available in snow with a manual trans 4x4 is unbelievable to the uninitiated. The traction "feel" available through the accelerator was unparalleled by any automatic trans 4x4 I've ever driven.
According to my Ford buddies, both the transfer case (at least the 2 speed in my FX4) and the eLSD are, as mentioned above, "clutch" systems, the eLSD uses clutches acting on an actual geared differential, while the wet clutch system in the transfer case allows speed as well as torque "differentials" without actually containing a geared differential as many of you realized already.
However, when operating properly, both are designed to absolutely lock for a true 50/50 torque split and zero difference in velocity between the front and rear axles in the case of the transfer case and between the RH and LH rear axles in the eLSD's case. In the case of the eLSD, this can take place under certain conditions in certain knob modes as well as when the lock button is engaged. Similarly, the transfer case will completely lock the axles as well. Not surprisingly, high steering angles will "unlock" the transfer case and in certain modes the eLSD as well.
I'd still like the independent ability to "lock" the transfer case in high (4H). As many of us, I've driven a lot of vehicles in a lot of conditions (including a VW Polo, VW GTI, and Porsche 911 on the Nürburgring). Locking the "center differential" (hopefully gear diff aficionados will forgive the term) tends to keep the vehicle going in a straight line, resisting deflections from semi-frozen slush, etc. It also equalizes the braking force through all wheels allowing more braking force to be applied before and during ABS events. Finally, front wheels have less rolling resistance than undriven front wheels. Not knowing when some software programmer/tuner decided to disengage the "lock", or re engage it is what I find unsettling during certain higher performance situations.
Finally, the best 4x4 vehicle's I ever drove in the snow were 4x4 F150's of various vintages with manual transmissions and limited slip rear ends. The very best was an '86 F150. The 4x4 selector was shaped and positioned so that you could operate it with either your right foot or hand, moving from 2H to 4H and back instantly, no engagement lag. The engine braking and control available in snow with a manual trans 4x4 is unbelievable to the uninitiated. The traction "feel" available through the accelerator was unparalleled by any automatic trans 4x4 I've ever driven.
Interesting - my experience has been the opposite - if I put on a locking diff on a turn, either on decel or acceleration, the rear swings out faster, as locking the diff will cause each axle to go against its respective turning circle, breaking traction.
I find 4wd activation lock also makes braking a bit more unpredictable, both in traction limit braking on slippery surfaces, and difficulty in keeping the vehicle straight.
In snow/slush, I find AWD/4WD will require me to apply more steering. Traction of a tire's footprint on the road is limited. On a RWD car, the front tires do not have any forces applied to go forward. All the traction is focused on lateral stability. Of course when you brake, all drivetrain variations you end up losing more lateral grip, which is why if you slam the brakes, you lose front end lateral grip, which normally is seen by the car pushing or understeering. This is because there's a longitudinal force on the tires in braking, limiting the lateral grip.
The other extreme case is FWD cars - once you apply gas to a FWD car in slippery conditions, the car will often push straight, requiring more turning angle input to keep the car on its path.
in AWD, you get the best forward traction, but in gas application, the front will typically push a bit more (however less than FWD), requiring more steering input, and the car can start drifting off center, especially following the crown/angle of the road.
I'm not saying RWD is the best, especially in accelerating, and the rear end tends to move around more relative to the front, but the front track is typically the most stable, using all it's traction available for lateral grip.
Meeker
Full Access Members
Definitely can see the braking advantage when all 4 wheels are forced to turn equally. But if you unlock even just one diff (front or rear) I think you lose the advantage don't you? And with all locked, any attempt to turn will break one or more wheels free because of turning radius differences. Doesn't that more than erase the braking advantage on the highway? Interesting discussion regardless...
Meeker
Full Access Members
I think either can happen, depending on whether the front steering wheels break free first, or the rear wheels. In my case I was coming downhill, turning onto my street. I didn't apply gas when starting the turn since I'm coasting downhill, so the lateral force of the front wheels attempting to turn broke them free first. If you were going uphill and applying gas, I'm sure it would happen like you experienced. Hey, that's why we drivers get paid the big bux!
Yeah right...
Open or unlocked differentials split torque evenly to all 4 wheels, so when you aren’t applying power (like in a slow down situation) brake force should be distributed pretty evenly. At least that’s my understanding. Even open diffs are technically “matching” power to all 4 wheels. It’s just that it only takes a few lb ft of torque to spin one side when it has no traction, so that’s all the other side gets sent to it (not enough to spin that sides wheel). This is what causes the one wheel peel effect you see commonly. On an open diff the tire with least traction on each axle determines the power both wheels on that axle gets. That’s the Achilles heel. This is where lockers and limited slips come in handy and fix the issues of open diffs, because they allow torque to differ between wheels on the same axle to get them to spin at the same rate in these situations where even torque doesn’t cut the mustard. But alas in braking, whether you are locked up via a locker or open and not locked a 50/50 locked transfer case is going to slice some distance off your stop. The testing I watched they did were on Jeeps with open diffs and ABS. The difference was quite large between 2WD and 4WD stopping distances.
I used to call BS when people said 4WD helps you stop, but then people sent me some videos and independent tests and I was proven wrong and surprised. I tried to lay it out to the best of my understanding, but I was a finance major not an engineer haha.
Last edited:
Essentially—on acceleration the wheel with least traction determines power supplied to both, but on deceleration the effects should be reversed. The best traction becomes the brake force applied to both. Mix that in between two axles where the rear can help more than it’s typical 30% for closer to 50% even and that’s supposedly where the distance gets better.
ROBERT BONNER
Full Access Members
Yes, an unlocked differential does, by definition ALLOWS a difference in speed right to left; but, in the case of a 4x4 truck or suv, when the rear is locked or in limited slip, the center is locked and the front diff is open, the AVERAGE speed of the front wheels MUST match the speed of the rear wheels. When compared to 2wd mode, in 4wd mode you have a lot more rotating inertia, axles, differential carrier, and front prop shaft (which is spinning at a multiple ie. 3.73 times as fast as the axles) acting as a flywheel. At high (freeway) speeds that inertia makes a difference, the front wheels that have to spin the same average speed have inertial loads that tend to keep the right and left front axles at the same speed, Newton #1. Mathematically it all comes down to the difference in resistance right to left vs. the amount of torque that it takes to "overspeed" one wheel through increased resistance slowing the opposite wheel. My experience is that in heavy snow with rutted snow in the roadway causing differences in rolling resistance from left to right, the open front diff doesn't allow a lot of difference in speed right to left when traveling at highway speeds. At slower speeds and lower rotating inertia l levels, things are very different, as they always are in smooth frictionless ice conditions.
