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I was hoping to read the comments here to understand once and for all what the difference between AWD and 4WD is. I'm still as confused as I was before reading

by hi_hi 2y ago

I was hoping to read the comments here to understand once and for all what the difference between AWD and 4WD is. I'm still as confused as I was before reading the comments. It appears the answer is...it depends on the manufacturer/vehicle.

xnzakg 2y ago
From TFA: > The most consequential distinction between AWD systems and more capable 4WD systems is that most vehicles equipped with 4WD have one or more locking differentials that massively aid in off-road traction. While AWD systems are great for increasing driver confidence on slippery road surfaces and in light off-roading, they are easily flummoxed in more challenging off-road terrain, especially low-speed and low-traction situations.
- carabiner 2y ago
  Numerous sources saying this is wrong. 4WD is not just AWD with locking diffs. Park service should call for cars that only have locking diffs if that's what they mean.
  - deleted 2y ago
    [deleted]
- quicklime 2y ago
  Pretty sure the Subaru Crosstrek mentioned in the article doesn't have one, but a WRX STI (also marketed as "AWD") has a lockable center diff. I agree with the other comment: if the Parks Service wants locking diffs (or ride height or whatever else) they should say so, not rely on inconsistent marketing terms.
ip26 2y ago
4WD mechanically interlocks the front and rear wheels (setting aside the front and rear differentials). You cannot use 4WD on clean pavement because of this; the front and rear may need to turn at different rates which 4WD doesn’t allow. It’s ok off road because the wheels can slip a little in the dirt. AWD generally does not mechanically 1:1 interlock anything, instead using things like torque converters. This allows it to be used on clean pavement. It isn’t as robust as 4WD, and has to respond to wheel slip instead of simply being 1:1 all the time.
doe_eyes 2y ago
Yes, and even some of the responses to your comment are wrong (or rather, they are right only for certain brands). Which probably means that enforcement is going to be... hilarious. What we can decipher is what the NPS is angling for. Many cars labeled "AWD" provide power to all four wheels, but if one of the wheels is not making contact with the ground, the remaining ones get little or no power. This is because the axles incorporate differentials - and if you have uneven traction, the torque delivered to the differential follows the path of least resistance. The end result is that it's deceptively easy to get stuck on uneven terrain, in mud, or in snow. But then, some "AWD" cars actually provide good workarounds. In the simplest variant, the car automatically applies brakes to the free-spinning wheel, forcing the differential to power the other wheel. Less wasteful and more responsive solutions that mechanically sense torque imbalance also exist. And then, some "4WD" cars work roughly the same way! For example, some models of RAM 3500 are labeled as four-wheel drive (4x4), but rely on torque-sensing ("Torsen") limited-slip differentials. Other 4x4 cars might have a button to physically lock the differentials. This is widely regarded as the best option, except it's dangerous on paved roads (and makes turning hard).
thefroh 2y ago
they're ambiguous terms, and the ruling will be "I'll know it if I see it!" it's more useful to consider what people suggest for a track. - "you're going to need a diff lock" - "you're going to need high clearance"
- xattt 2y ago
  “What do you mean that I can’t get on this trail in my AWD Nissan Maxima?”
Daneel_ 2y ago
Engineering Explained on Youtube has a very comprehensive video covering this: https://www.youtube.com/watch?v=Jk246sutET0 https://www.youtube.com/watch?v=Jk246sutET0 At a very simple level it boils down to: Do you have a transfer case? If yes, then it's a 4WD.
- karolist 2y ago
  A transfer case is something BMW calls the thing that attaches to the side of your transmission to provide power to front wheel shafts, this does not mean the car is 4WD. Yes, still confusing. https://awd.tech/de/apps/catalog/transmission/atc300-bmw https://awd.tech/de/apps/catalog/transmission/atc300-bmw
blitzar 2y ago
> it depends on the manufacturer/vehicle & the marketting department.
Beretta_Vexee 2y ago
The cars are equipped with a differential that distributes power differently between the wheels. This is particularly useful for preventing the wheels from squealing when cornering. In a bend, the four wheels do not turn at the same speed between the inside and outside of the bend. This gives you better grip, a smoother ride, etc. It's really essential. - When you have two wheel drive you only have one differential between the two wheels. - When you have four-wheel drive you have three differentials, one between the front wheels, one between the rear wheels and one between the front and rear. So far so simple. Now one of the problems with differentials is that if one of the wheels loses traction, it gets all the power back and spins in a vacuum. Finding yourself with a wheel in the sand, in the air, on the snow, etc. is very common when driving off-road or in the mountains. This problem has been solved with the differential lock, which can be manual or automatic. When locked, the differential is locked and power is transmitted equally to the wheels. So you can get out of your sandy or snowy hole. That's what we call a 4x4. A All-wheel-drive has no differential locking system.So if one wheel loses its grip, the vehicle is stuck. There's nothing you can do - all the power will go to the wheel with the least grip. So AWD is particularly unsuitable for off-road use and shouldn't be sold as such. Some off-road vehicles do not have a differential, such as quad bikes or buggies. Perfect for mud, not so great on the road. https://en.wikipedia.org/wiki/Differential_(mechanical_device) https://en.wikipedia.org/wiki/Differential_(mechanical_devic... https://en.wikipedia.org/wiki/Locking_differential https://en.wikipedia.org/wiki/Locking_differential
- criddell 2y ago
  There are exceptions. I believe the Kia Telluride SUV is sold as AWD and it has a locking differential system (or at least it’s an option). There are probably others as well.
  - tossstone 2y ago
    The Kia Telluride does not have a locking differential in the same sense as conventional 4x4 vehicles. In fact, the Kia Telluride comes with a multi-plate center clutch that allows for distribution of power between the front and rear wheels. When the clutch is fully engaged, in most cases there should be no slippage which means that power is distributed evenly (50/50) between the front and rear. However, there's always the possibility that the clutch can slip given enough of a torque differential between the front and the back. It can offer improved traction in poor road conditions. A proper locking differential found in most traditional 4x4 vehicles/trucks, when engaged, physically locks the axles together which means they cannot spin at different rates. This is essential for many more rigorous off-road applications when you may have to rely on traction from a single wheel to get you unstuck. This is exactly the type of misleading marketing that is described in many other comments. A clutch pack cannot physically lock axles together in the same way as a locking diff.
itsoktocry 2y ago
>I'm still as confused as I was before reading the comments. I agree, and I know a bit about this! The reality is very few vehicles on the market are legit "off-road" capable. But, the other side of that is not every trail is legit "off-road", either. Just because there's no pavement, doesn't mean it's "off-road". There's an entire spectrum of vehicles and trails where normal people can get off the beaten path.
smitelli 2y ago
Up until not long ago, you could get away with this test: "Do I, as the driver, have to stop, think, and make some choice to command the car to change some setting that governs whether or not I get across this patch of terrain?" The 'stop' step is important; certain classical 4WD shifts require the vehicle to be stationary. The automatic-ness of the AWD systems -- no pesky second shifter -- was the differentiator. Now that we have knobs for different "driving modes," the the ability to slam it into whatever position whenever we want while an ECU figures out how to keep a gearbox from exploding, it's genuinely hard. Still, the presentation of a setting like "lock/unlock" and "two/four" and "high/low" is the standard I still go by (right or wrong).

by hi_hi 2y ago

xnzakg 2y ago

From TFA: > The most consequential distinction between AWD systems and more capable 4WD systems is that most vehicles equipped with 4WD have one or more locking differentials that massively aid in off-road traction. While AWD systems are great for increasing driver confidence on slippery road surfaces and in light off-roading, they are easily flummoxed in more challenging off-road terrain, especially low-speed and low-traction situations.

carabiner 2y ago
Numerous sources saying this is wrong. 4WD is not just AWD with locking diffs. Park service should call for cars that only have locking diffs if that's what they mean.
- deleted 2y ago
  [deleted]
quicklime 2y ago
Pretty sure the Subaru Crosstrek mentioned in the article doesn't have one, but a WRX STI (also marketed as "AWD") has a lockable center diff. I agree with the other comment: if the Parks Service wants locking diffs (or ride height or whatever else) they should say so, not rely on inconsistent marketing terms.

ip26 2y ago

4WD mechanically interlocks the front and rear wheels (setting aside the front and rear differentials). You cannot use 4WD on clean pavement because of this; the front and rear may need to turn at different rates which 4WD doesn’t allow. It’s ok off road because the wheels can slip a little in the dirt. AWD generally does not mechanically 1:1 interlock anything, instead using things like torque converters. This allows it to be used on clean pavement. It isn’t as robust as 4WD, and has to respond to wheel slip instead of simply being 1:1 all the time.

doe_eyes 2y ago

Yes, and even some of the responses to your comment are wrong (or rather, they are right only for certain brands). Which probably means that enforcement is going to be... hilarious. What we can decipher is what the NPS is angling for. Many cars labeled "AWD" provide power to all four wheels, but if one of the wheels is not making contact with the ground, the remaining ones get little or no power. This is because the axles incorporate differentials - and if you have uneven traction, the torque delivered to the differential follows the path of least resistance. The end result is that it's deceptively easy to get stuck on uneven terrain, in mud, or in snow. But then, some "AWD" cars actually provide good workarounds. In the simplest variant, the car automatically applies brakes to the free-spinning wheel, forcing the differential to power the other wheel. Less wasteful and more responsive solutions that mechanically sense torque imbalance also exist. And then, some "4WD" cars work roughly the same way! For example, some models of RAM 3500 are labeled as four-wheel drive (4x4), but rely on torque-sensing ("Torsen") limited-slip differentials. Other 4x4 cars might have a button to physically lock the differentials. This is widely regarded as the best option, except it's dangerous on paved roads (and makes turning hard).

thefroh 2y ago

they're ambiguous terms, and the ruling will be "I'll know it if I see it!" it's more useful to consider what people suggest for a track. - "you're going to need a diff lock" - "you're going to need high clearance"

xattt 2y ago
“What do you mean that I can’t get on this trail in my AWD Nissan Maxima?”

Daneel_ 2y ago

Engineering Explained on Youtube has a very comprehensive video covering this: https://www.youtube.com/watch?v=Jk246sutET0 https://www.youtube.com/watch?v=Jk246sutET0 At a very simple level it boils down to: Do you have a transfer case? If yes, then it's a 4WD.

karolist 2y ago
A transfer case is something BMW calls the thing that attaches to the side of your transmission to provide power to front wheel shafts, this does not mean the car is 4WD. Yes, still confusing. https://awd.tech/de/apps/catalog/transmission/atc300-bmw https://awd.tech/de/apps/catalog/transmission/atc300-bmw

blitzar 2y ago

> it depends on the manufacturer/vehicle & the marketting department.

Beretta_Vexee 2y ago

The cars are equipped with a differential that distributes power differently between the wheels. This is particularly useful for preventing the wheels from squealing when cornering. In a bend, the four wheels do not turn at the same speed between the inside and outside of the bend. This gives you better grip, a smoother ride, etc. It's really essential. - When you have two wheel drive you only have one differential between the two wheels. - When you have four-wheel drive you have three differentials, one between the front wheels, one between the rear wheels and one between the front and rear. So far so simple. Now one of the problems with differentials is that if one of the wheels loses traction, it gets all the power back and spins in a vacuum. Finding yourself with a wheel in the sand, in the air, on the snow, etc. is very common when driving off-road or in the mountains. This problem has been solved with the differential lock, which can be manual or automatic. When locked, the differential is locked and power is transmitted equally to the wheels. So you can get out of your sandy or snowy hole. That's what we call a 4x4. A All-wheel-drive has no differential locking system.So if one wheel loses its grip, the vehicle is stuck. There's nothing you can do - all the power will go to the wheel with the least grip. So AWD is particularly unsuitable for off-road use and shouldn't be sold as such. Some off-road vehicles do not have a differential, such as quad bikes or buggies. Perfect for mud, not so great on the road. https://en.wikipedia.org/wiki/Differential_(mechanical_device) https://en.wikipedia.org/wiki/Differential_(mechanical_devic... https://en.wikipedia.org/wiki/Locking_differential https://en.wikipedia.org/wiki/Locking_differential

criddell 2y ago
There are exceptions. I believe the Kia Telluride SUV is sold as AWD and it has a locking differential system (or at least it’s an option). There are probably others as well.
- tossstone 2y ago
  The Kia Telluride does not have a locking differential in the same sense as conventional 4x4 vehicles. In fact, the Kia Telluride comes with a multi-plate center clutch that allows for distribution of power between the front and rear wheels. When the clutch is fully engaged, in most cases there should be no slippage which means that power is distributed evenly (50/50) between the front and rear. However, there's always the possibility that the clutch can slip given enough of a torque differential between the front and the back. It can offer improved traction in poor road conditions. A proper locking differential found in most traditional 4x4 vehicles/trucks, when engaged, physically locks the axles together which means they cannot spin at different rates. This is essential for many more rigorous off-road applications when you may have to rely on traction from a single wheel to get you unstuck. This is exactly the type of misleading marketing that is described in many other comments. A clutch pack cannot physically lock axles together in the same way as a locking diff.

itsoktocry 2y ago

>I'm still as confused as I was before reading the comments. I agree, and I know a bit about this! The reality is very few vehicles on the market are legit "off-road" capable. But, the other side of that is not every trail is legit "off-road", either. Just because there's no pavement, doesn't mean it's "off-road". There's an entire spectrum of vehicles and trails where normal people can get off the beaten path.

smitelli 2y ago

Up until not long ago, you could get away with this test: "Do I, as the driver, have to stop, think, and make some choice to command the car to change some setting that governs whether or not I get across this patch of terrain?" The 'stop' step is important; certain classical 4WD shifts require the vehicle to be stationary. The automatic-ness of the AWD systems -- no pesky second shifter -- was the differentiator. Now that we have knobs for different "driving modes," the the ability to slam it into whatever position whenever we want while an ECU figures out how to keep a gearbox from exploding, it's genuinely hard. Still, the presentation of a setting like "lock/unlock" and "two/four" and "high/low" is the standard I still go by (right or wrong).