[GiveUsANormalSizedBed]

It’s not just selective brake control on the front, it’s selective power delivery. Same on the rear unless the locker is engaged.

How is “selective power delivery” different than “selective brake control”? In ICE vehicles that claim to have selective power delivery with an open differential, they do so by selectively braking one wheel to send torque to the other wheel. I’m inclined to think the front operates the same way in the Lightning. If they had technology to accomplish it in a different way, you would think that they would have used the same tech on the rear rather than adding a locker.

 

[GiveUsANormalSizedBed]

These terms are actually becoming obsolete with these electric drive units.

Historically, "4x4" was used to refer to systems that would mechanically lock torque bias equally front and rear, while "AWD" was used in vehicles capable of moving only a portion of available torque from one axle to the next; usually through a clutch system.

The Lighting, as with the Tesla that I drive now, is capable of providing 100% torque to all four wheels at once, operationally putting in in the same category as a 4x4 with fully locked differentials.

Since the Lightning (and the model Y) have a "mode" that equalizes torque front to rear, they are "4x4s". It could be argued that since the tesla model 3 has no such "mode" (yet), it is the new definition of "AWD". This said, the lines between the two have become significantly blurred with advancing technology. A better question becomes, "does the vehicle have an Off-road mode that provides for instant torque to all the wheels?... which is all you can ask from the very best 4x4s.

In the case of the Lightning, the answer is yes.

Old post, but while I agree that the terms are becoming obsolete, you’re confusing speed with torque. Open differentials have a 1:1 torque bias ratio. They allow for different axle speeds, but always distribute the same amount of torque to each axle. Consider the situation where one tire is on ice and one tire has traction. The amount of torque it takes to spin the tire on ice is the same amount of torque that the open differential will send to the tire with traction. That will not be enough torque to spin the tire with traction and you will remain stuck.


A locker gets you moving because, while it forces the same axle speed, it allows for more torque to transfer to the tire with traction. They allow for variable torque, up to the extreme where you have all the torque (discounting parasitic loss of course) going to the tire with traction. So technically they have an infinite torque bias. Limited slip differentials and ABS braking work well to give variable torque when needed, but they can never send 100% of torque to the tire with traction like a locker can.

I agree that the Lightning and your Model Y would fall into the conventional 4x4 category, but without a front locker (or quad motors like the Rivian), neither can actually provide 100% torque to given wheel. A 4x4 with dual lockers is still in another category of improved traction.

 

[GiveUsANormalSizedBed]

First of all, you have two separate motors that can be powered differently. In an ICE 4X4, there is a single power source, so all you can do is change how that power is distributed and used at the four wheels. In a two-motor BEV, each motor can be powered at different rates.

Correct, the Lightning uses both motors to selectively deliver power to the front and rear. In your earlier comment, you said power distribution between the front wheels was not only done by selective brake control. I don’t see how that is possible with only one motor at the front and no locker or limited slip mechanism. I believe the dual motor with rear locker configuration in the Lightning is essentially three wheel drive, with selective ABS braking/ eLSD attempting to mitigate the open diff up front just as Shocker said.

 

[GiveUsANormalSizedBed]

How do you get three wheel drive? I’m intrigued.

What I mean by 3 Wheel drive is that if only one front tire had traction and no rear tires had traction, the truck would not go anywhere. All the torque of the rear motor would go to spinning the rear tires which have no traction and the torque of the front motor would only spin the front tire with no traction. The torque going from the front motor to the tire with traction would not be enough to get it to spin, because the design of an open differential limits that torque to equal the amount of torque needed to spin the tire with no traction. Therefore, the three tires with no traction would be spinning in place, the tire with traction would not be moving, and the truck would be stuck. This as opposed to a front locker where the tire with traction would get all of the torque of the front motor minus the minimal amount of torque taken to spin the other front tire with no traction.

However, as @shocker mentioned, Ford attempts to mitigate this using selective ABS braking. The principle is based off of the fact that open differentials always send equal amounts of torque to each axle shaft. By braking the wheel that is spinning, the vehicle increases the torque applied to that wheel and consequently also increases the torque to the wheel with traction until there's enough torque going to that wheel that the vehicle starts to move. Ford calls this eLSD, but it's the same process that goes into Toyota's ATRAC system. The technology works very well, but it's still not as good as two mechanically locked differentials in a 4wd system that can distribute up to basically 100% of available torque to any given wheel. Selective ABS braking requires slippage first so it can not keep momentum like a physical locker and, in extreme cases, can overheat the ABS system.