Okay I'm having a bit of a hard time understanding exactly the difference between 4x4 and an AWD system. I know that 4x4 is not on all the time, it is selectable, which is what our trucks have. And I know AWD is generally on cars and suvs and is on all the time. So my question is, why can't 4x4 be on all the time, but AWD on things like Audi Quattros (and dare I say it) GMC Cyclones be on all the time? I'm just trying to figure out the difference

 

If you have 4 wheels and all of them drive, then 4 wheel drive and all wheel drive ought to be the same thing, right? The difference in name is an artificial one made up to try to clarify a difference in design, but it's used to sort of describe two different differences, so it's not so clear anyway.

4WD pretty much always means a transfer case that has two speeds (high and low range). It generally is used in "truck" applications where toughness outweighs ease of use.

AWD usually means a system in a more road oriented vehicle, ofter driven by someone who doesn't want to think about driving much. It usually does not have a low range.

AWD is also used to describe a position on a 4WD transfer case gear shift that gives you an open differential between the front and rear drive shafts so you can drive in 4WD on non-slippery surfaces.

And that gets to why "4WD" can't be on all the time an "AWD" can. When you go around corners your front wheels travel farther than your rear wheels. Unless there's a differential between the front and read drivelines you will get binding which is at best very annoying while wearing out your tires, and at worst it can break parts in the driveline. "4WD" generally does not have a differential so you can't use it unless the road is slippery enough to release the binding more gently. "AWD" has a differential.

 

So basically you cannot take an np205 (for example), always have it in 4wd, and drive it on the street

 

That is correct.

On the other hand, the NP203 was a full time 4WD case (just to throw more terms into the mix). It's a heavy duty truck-oriented 2 speed transfer case with a differential (that can be manually locked). "Full-time" vs. "part-time" used to be the distinction because none of the "part-time" cases had diffs. But then they came out with cases that could select 2WD or 4WD with a diff. What do you call that? It's part-time and it's full-time? That's more-or-less when the "all-wheel-drive" distinction came about.

There are some 4WD cases that have diffs. Jeep was the main one to use them and I don't think any of them are quite up to a 3/4 ton rating, but there might be something out there that I don't know about.

 

basically put, 4 wheel drive is for trucks and people that go off road.
all wheel drive is for glorified cars and people that do not know how to drive, and end up in the ditch alongside the road because they drive too fast for road conditions because they have all wheel drive and think they can go anywhere.

 

I think you're being too harsh there. I think we agree that people that don't know how to drive, who overdrive the conditions and their vehicles abilities are likely to end up in the ditch. But you can't equate that to "only people who don't know how to drive buy AWD vehicles."

AWD (or 4WD for that matter) improves vehicle stability on slippery roads. It also improves the vehicles ability to start on ice, make it up a slippery hill, get through an unplowed parking lot, pull a boat up an unpaved landing and probably a bunch of other things as well. AWD is for people that want advantages like those but don't want to need to think about when they need to shift in an out of 4WD.

AWD (or 4WD) does not make a vehicle invinceable. And although good drivers can and do buy AWD vehicles, there's nothing preventing people who don't know how to drive from buying them too. And if someone who doesn't know how to drive thinks AWD makes them invinceable, yes, they'll put their AWD in the ditch.

4WD systems are for trucks and off road vehicles. They tend to be more rugged, but they do require more driver input. I own trucks and off-road vehicles so I'll never have AWD. But my 81 year old dad and my wife don't want to think about shifting a transfer case but they want the benefits of four wheel drive in Minnesota winters. My dad's AWD Subaru Forester and my wife's AWD Ford Escape are perfect for them. And neither has been in the ditch.

 

i should have added a after that Bob. it was meant more as a joke than fact.

 

would like to point out that the 2spd part of this does NOT enter into the equation. There are several 4wd transfer cases that do NOT have a low range (Dana 21 for example)
And my wife's old old 2003 expedition had AWD and also had positions for 4wd (locked the internal differential) and 4wd lo. Currently own a 02 explorer that is also AWD but had 4wd and 4lo options.

 

OK. There's enough truth in it that it fits as a joke. But there certainly is a legitimate use of AWD and I wouldn't want to be insulting anyone. The helps!

My point is that there have been different terms used to mean different things at different times (for Pete's sake, "FWD" meant "Four Wheel Drive back in the '20s!). But yes, there are newer "4WD" systems that have an "AWD" position on the gear selector. I hadn't realized that the Expedition used one, I had thought most of them were lighter duty, often used in Grand Cherokees and such. But I keep learning!

 

This can get overly complicated so I can try to CliffNote it...

4WD functions through a transfer case, typically allowing for 2Hi, 4Hi, and 4Lo. Some vehicles have a 4-Full option of sorts which is meant for less than desirable on-road conditions. My '94 XJ (Cherokee) had the NP231 case which had the three typical modes I listed initially. It would lock the axles to themselves, meaning if a wheel on the front started to spin it would not effect the rear. The optional NP242 case had the Fulltime option, and the axles were tied together - one wheel spun, you'd run out of steam faster compared to running it in Hi or Lo. But Fulltime was meant for snowy roads, rain, gravel roads, etc.

AWD utilizes a center diff to distribute power fore and aft, most modern vehicles a have a system that will also shift the power to whichever end needs the help based on driving conditions. My STi had a selectable diff control that would alter the characteristics and how the system distributed power and responded.

AWD is starting to get ridiculously in-depth and involved on the higher end cars these days. The system in the Nissan GTR will take a ridiculous amount of parameters and data into account and can actually shift all of the power to one or both outside wheels, whichever has the most traction, in order to make the car stick and fly around the corner. A 4WD system isn't going to do that, although the technology has come a long way.

 

yup I drove an escape with the stability control this past spring. Nice car generally, went through mud on jobsite like a champ without slipping a wheel even on factory street tires. Then one night i had it by myself and booted on it, on one of those tiny little goat trails in Penn. All was good until one corner where I realized I was 1 second too long coming off the gas and onto the brakes. I knew I was done for and was trying to think how I would explain to my boss writing off the rental. Then stability control kicked in, tucked her back in and around the corner I went. Slowed her down a bit the rest of the way home :-) amazing technolgy

 

I Imagine the owner/driver here might beg to differ


The above is using a Land Rover full time 4WD LT230 transfer case.
Same one that's in these


and these


Another difference between part time and full time 4WD is that most, if not all, full time 4WD vehicles use CV joints in the front axle rather than cardan type u-joint to prevent steering jerk as the u-joint varies speed when turning.