[alkonaut]

I think "AWD" today is used to mean "anything that isn't 2WD". So whether it's a full time 4x4 or something that is mostly-fwd-but-rwd-when-slipping or something else isn't part of the nomenclature. It simply means "something more than 2WD at least some of the time". There has been an endless debate as to whether 4WD or AWD are the same or different, whether only "symmetric" or "full time" counts as one or the other. But these days with hybrid drives, traction control shifting drive front/back etc., it's just too complex to keep apart any more.

[supermatt]

Not really - AWD is effectively non-braking traction control by varying the power distribution to each axle (and on some modern electric drivetrains, each wheel). 4wd provides constant power to both axles.

[alkonaut]

I think of it more as an outdated distinction. First of all with motors on each wheel and no communication between front/rear in many cases, the distinction becomes blurry.

Further many manufacturers have names like “AWD” (volvo and others) or “4matic” (MB) or “4motion” (VW) to label their take on more-than-2wd, whether or not their variant is awd or 4WD (or both) in the traditional sense. Some "AWD" models will be electric with 1 motor per axle, or 3 motors (1 front 2 rear) etc. Some others are ICE with traditional drive shaft to the rear wheel axle, which in some cases will drive 50/50 and in some cases variable. Others still are hybrids wth no prop shaft but instead a rear electric motor etc.

[supermatt]

Its not outdated. There may be multiple variations on AWD (as i mentioned, some can vary power to individual wheels, rather than just the axles), but 4WD (or 4x4) is categorically not AWD.

[alkonaut]

Doesn't traction control further blur that? Given that traction control is now required almost everywhere, and involves cutting power to individual wheels (Not like ESP using brakes), at what point does traction control cutting power to individual wheels or axles dynamically in a 4x4/4WD system make it an "AWD" instead?

Perhaps those vehicles that use 4x4 in the tradtional sense are such that you have to engage it and that effectively cuts also any traction control - and then you disengage for normal driving?

[supermatt]

Traction control on an AWD system can be composed of power management (overall torque output), power distribution (how much power goes to each axle/wheel) and braking (slowing down individual wheels).

Traction control on a 4WD can only consist of power management and braking, because there is no way to vary the distribution (otherwise it would be AWD, not 4WD).

There are some systems that under certain conditions will switch from 2WD to 4WD. Those systems are NOT considered AWD and dont have the benefits thereof.

FYI, ESP (Electronic Stability Program) is just a brand term for an ESC (Electronic Stability Control) which covers both TCS and ABS. When people talk about "traction control" they usually mean the entire ESC subsystem.

[alkonaut]

I think part of why I consider them to be one and the same is because in the total absence of "true" 4WD/4x4 (approximately no one drives pickup trucks in Europe, I'm guessing that's where the true 4x4 still lives in the US) so the 4WD/2WD moniker has been used for 2WD/AWD as in "Will you get the 2WD or 4WD tesla is used somewhat sloppily?". It seems car manufacturers though are still careful not to call anything 4WD or 4x4 when it's not.

[brookst]

I think there is more nuance here. A 4x4 with a locked center diff and open front and rear diffs acts just like many AWD implementations.

That same 4x4 with limited slip diffs on front and/or rear is just like other AWD implementations.

And that same 4x4 with locked front and/or rear diffs is just like yet other AWD implementations.

[supermatt]

> A 4x4 with a locked center diff and open front and rear diffs acts just like many AWD implementations.

Thats simply not true. It wouldnt be AWD if it cant adjust the power supplied to each axle. Thats the primary distinction.

[brookst]

Not all AWD implementations can adjust power per axle. The vast majority just use a center diff that is either open or limited slip. Both of those configurations are also used in some 4WD systems.

The primary distinction is that AWD is full time, while 4WD is part time and vehicles run in 2WD until the transfer case connects the second diff/axle.

Actual torque vectoring AWD systems are fairly rare and expensive compared to the AWD that has existed for 50 years, though they are becoming more common.

Here’s a good illustration of the different AWD implementations; I think you’ll find that a simple open center diff is still considered AWD and is still pretty common: https://www.caranddriver.com/features/a15102281/best-all-whe...

[sandworm101]

>> First of all with motors on each wheel and no communication between front/rear in many cases, the distinction becomes blurry.

Which cars have motors on each wheel? That is maybe 0.01% of vehicles on the road. (Electric busses?) And even then, AWD/FWD distinctions can matter in how those motors interact. Electric or IC, so long as power is delivered through four wheels there will be different styles and techniques for balancing that power for whatever reasons occur at a particular time.

[supermatt]

Nothing yet, but the next porsche electric drivetrain supposedly will:

https://newsroom.porsche.com/en/2019/technology/porsche-engi...

[meetingthrower]

Agree. We have a Tacoma that has 4WD and it is the absolute dumbest implementation. Contrast that to the Subaru with AWD and it is a completely different driving experience. We go with studs on the Tacoma for that reason, and get by with regular snows on the Subie.