4wd Vs. Awd

[RjsItalyzFinest1]

ok... i used to own a lincoln navigator and it had 4wd it went through mud and stuff in our vacation property it wen through well.... i just purchesed a 2003 escalade w/ AWD the AWD system dosnt seem to work as well as the 4wd system did.... is there a reason AWD dosnt work as well?? is the the permenet split in torque?? how doews AWD do in different depths of snow....
THANX!

[JohnnyWash1]

There are way too many factors involved to say which system is better, bar none. First of all, both systems are AWD. AWD relies on either torque sensing differentials or sensors or both, to transfer power to the wheels with the most traction. It is more like traction control.
4WD is a permanent torque split between axles, not actual tires. Usually in a 4wd system you would lock the front hub, so that there is a 50/50 split in torque between the front and rear axles.

Jon

[ivymike1031]

try this
http://www.howstuffworks.com/four-wheel-drive.htm

in a 4wd system you would lock the front hub, so that there is a 50/50 split in torque between the front and rear axles

Actually, I thought the "usual" way to do it was to force the driveshafts speed to be equal (so the rotational speed input to each axle is the same)? That wouldn't be a 50/50 torque split unless all wheels had the same traction.

[JohnnyWash1]

Interesting idea, IvyMike. You may be right. We'll have to do more research.

Jon

[Meyaht]

4wd works through a transfer case at the tailshaft of the transmission. usually the gears for the front wheels in a 4wd system move faster then the rear to allow for more wheel speed during turns.

AWD is a front wheel drive system that usually has some type of iol pump/torque converter in therear differential which turbs the rear wheels when the driveshaft is moving, say, 50 rpm faster then the fronts. when the fronts lose traction, the driveshaft spins faster then the rear wheels are comparetively. so the torque converter kicks in and starts putting power to the rear. thus AWD.. a good diagram of this is on TV the next time you see a SUBARU commercial, right when thay say "the wheels that slip to the wheels that grip" check out that little diagram they have going. also check out the subaru forum on this site if there is one.

[JohnnyWash1]

AWD does not necessarily have to be a front wheel drive system. Both of the systems he mentioned are AWD, and both come from rear drive vehicles. As for the different kinds, I didn't hear you mention a viscious center diff or clutch type diff. Both are active in many AWD systems.

Jon

[Moppie]

The differnce is purly arbitury, and comes entirly down to what the marketing department wants to call it.

There however as many differnt ways of providing power to all 4 wheels as there are manufactors, some are better suited to some situations than others, while many are nothing more than a bad marketing trick and will do nothing more than increase tyre wear and fuel consumption.

However as a very general idea of a very general trend that has occured, generaly vechiles labled as being 4WD will have selectable 2WD/4WD and have an off road bias to thier set up (although most new off roaders are going full time 4WD) while AWD is used on purely road orintated vechiles and are set up more for performance, or safety. Its a term that only really showed up in the 80s, and was used largely by Audi and the Japanese as a way of seperating thier mostly performance 4WD cars from much simpler off road vechiles.

[JohnnyWash1]

IvyMike, here is a quote from your link:

"When four-wheel drive is engaged, the transfer case locks the front driveshaft to the rear driveshaft, so each axle receives half of the torque coming from the engine. At the same time, the front hubs lock."

Moppie, this is from the same article:

"Four-wheel drive - Usually, when carmakers say that a car has four-wheel drive, they are referring to a part-time system. For reasons we'll explore later in this article, these systems are meant only for use in low-traction conditions, such as off-road or on snow or ice.

All-wheel drive - These systems are sometimes called full-time four-wheel drive. All-wheel-drive systems are designed to function on all types of surfaces, both on- and off-road, and most of them cannot be switched off.

Not trying to flame at all guys, just the opposite. I am trying to find more info on this subject and explore it, because the answer eludes me and others, and seems suited enough for discussion.

Jon

[ivymike1031]

Well, to be perfectly honest, I haven't read that page in over a year (since the last time this discussion came up around here). If they say what you say they say, the transfer case locks the front driveshaft to the rear driveshaft, so each axle receives half of the torque coming from the engine, then they're wrong, except for the special case where there is equal traction at both axles. Say, for example, that the front wheels are entirely off the ground. The front and rear drive shafts are locked together, so they spin at the same speed. The back axle can still push the vehicle along, but the front axle is spinning freely (at the same speed) in mid-air. The rear axle, in this case, will be transmitting nearly 100% of the torque.

[jhillyer]

Independent of what marketing has decided to label: 4WD is four wheels receiving drive. AWD is all wheels, if one, then one, if three, then three, if 18, then 18 wheels get the drive. If a vehicle of four wheels receives drive to two wheels until traction loss and delivers drive to other wheels, it's 2WD. This is all ratio independent, but I'm just a schmuck.

Ah, I'm typing this and reading further -- Moppie is sensible. It _is_ marketing. I say stay critical and logical, forget the marketing, pulling marketing weasels more to our view. Observe what Audi has done in recent years to goof mainstream AWD Quattro.

[Chris]

Marketing if a funny thing, and is mostly BS.
But there are supposed to be a few fundamental differences in TRADITIONAL 4WD and AWD.
4WD is a part time system, if it isnt part time, its not a 'real' 4WD system. It uses a transfer case, that, when engaged, splits the power by a certain, fixed ratio between the front and rear tires (usually 50-50) Well, from how I understand, it is just a locking differential, so, it makes the same amount of rotations of the driveshaft go to each axle. So, if the front wheels are on ice, and the back wheels are nearly locked, more actual power is being sent to the rear wheels, and both the front and back spin at the same rate. (ie, the rear wheels are exerting a force of 10000newtons, the fronts, only 50 newtons).
A 4WD system is usually left in 2WD, to avoid wear on the transfer case, and possible, minor handling issues.

AWD, on the other hand, is a full time system, with power to wheels changing all the time. The power goes to a transfer case (which will usually be an open or limited slip differential, or a fancy clutch or hydralic system), from there to the front and rear axles, which will have usually an open or limited slip differential, or something fancier.
This works better for things like casual rough weather driving, since its always on.
For real offroad situations, its not as good, there is too much slip in the system, wheels with traction wont get as much power. Still, a good AWD system can be adequate for most cottaging adventures, with tires playing a pretty big role.

Of course, the perfect off road system is totally unpractical for normal use; a locking diff, and locking front and rear ends. Try this for normal driving, fully locked, and you'll end up breaking things, besides handling being terrible.
(note, most factory 'locking' diffs arent lockers, they're limited slips)

So, if you do real offroading, a 4WD system is better, for everyday use, AWD is better, plus, it provides AWD when you might not be expecting to need it, and in a 4WD vehicle, you'd be in 2WD.

[Moppie]

Originally Posted by JohnnyWash1

because the answer eludes me and others, and seems suited enough for discussion.

Jon

Absolutly, but sadly the differnce if there ever was one cames down largely to semantics and cultural language differnances, that due to differing terminology used by manufactors are becoming even more blurred.


Basicly proir to about the early 70s there was either 2WD or 4WD.
A 2WD was pretty about 99.9999% of the cars on the road, a 4WD was a specialist off road vechile, e.g. Jeeps and Land Rovers.

Then in the 70s FF (one F stands for Ferguson, as in the tractors, and I can't remember the other) based in the UK developed a system that used a center differential to allow continous use of 4WD on hard surfaces. (tradionaly the loss of traction in an off road environment allowed for slippage to occur between front and rear wheels, its why most early 4WDs were able to be run in 2WD as well, or they would destroy tyres, suspension parts and the transfer case when run on paved road).
The system was fitted to cars like the Jenson Interceptor (Ford V8 powered British GT) and custom fitted to Triumph 2500PI's and the odd Jag and Volvo for use in Northern Europe (would be awsome fun in the snow).
Then in the mid 80s manufactors cottoned on to traction advantage in loose surfaces offered by 4WD and started to use it in Rally cars, Audi being the most famous, but all the major manufactors competting in Rallying at the time got in on the act, and all built some form of road version for homogation purposes. Some were more succesful in the market than others, e.g. the Audi Quattro.
At about the same Subaru, who were not big in rallying back then, also cottoned on to the advantage 4WD offered and began to market a series of small vechiles that would go places regular cars couldn't. They very succesfuly filled an at the time very nich market.
Most manufactors stuck with calling thier 4WD cars 4WD through out the 80s, a good example being the Mazda 323 DOHC Turbo, a 4WD version of which was made avliable in about 1987? and in Japan often had quite visable 4WD badges.

Of course 4WD was, and still is much more expensive to manufactor, and many of the car buying public still associated it with vechiles like the Land Rover and Jeep, despite the at the time considerable differnces. 4WD in such vechiles was used primeraly for use Off Road, and so was selectable to 2WD to allow use on Road, while the 4WD cars used Full time 4WD via a usualy open center diff (even on many modern AWD/4WD cars its till possible to get stuck if one wheel loses traction, as it will spin since power is transfered to it via the center diff in the sam eway its transfered via the axles diff) as a mean of increasing performance and safety (more on the safety bit later).
A way was needed to seperate the two systems so that the more general (read ignorant) public could be sold more expensive 4WD cars.

I have no idea where the term AWD (all wheel drive) came from, but it is nothing more than a differnt way of describing what is happening, that is all the wheels are being driven, where as its possible to have a 4WD that still has 5th and 6th wheel at the front that arnt driven (e.g. a large 6 wheel truck which is then a 6x4) (4WD by the way was another marketing trick that evolved from the term 4X4, and was used to seperate vechiles like the Land Rover from thier somewhat humble military beginings (its also an English vs America thing).
My guess is AWD orginated it with either Audi or Subaru, but it seemed to appear magicly on the scene in the late 80s (but as term would probobly have been used far earlier, possibly as far back as FF in the 60s, or may be even earlier).



....where was I? oh yes, sorry more ranting....


Back then of course there was a clear distinction between AWD and 4WD, AWD was used on cars, and 4WD was used on off roaders. Pretty simple huh. Well as with everything in our ever changing society it ain't so anymore mate.
With modern 4WD systems the ablity to select a 2WD mode in almost all the off road vechiles avliable on the market today has vanished. Quite simply the modern systems have become so advanced its no longer nessacry to lock front and rear drive together to avhive great traction, instead usualy a computer controlled center diff is able to provide power to both axles, and allow for enough slippage to prevent wear and breakage of the drive line.
Hence you get extremly capable off road vechiles like the Porsche Ceyane(sp) and the new Range Rover that come with full time AWD/4WD, despite having more traction off road then ever before they don't have a 2WD option for road use, as its simply not needed. Combined with the arrival of "soft roaders" like the CRV and RAV 4 which also use full time systems yet claim a limited off road ablity the once simple line between AWD and 4WD has been blurred to the point of being arbitry.



On the note of safety Subaro among others has a great marketing compain promoting the safety the extra traction AWD/4WD provides. Quite simply its largely BS. A tyre only has its most traction when being driven (i.e. power is being applied). AWD/4WD will not improve your level of grip under brakeing, or when off the power, it will only do so when you are acclerating. Since about 90% of the cars subaru have ever made don't have anything like the power required to acclerate them if they get into a situation where the AWD would be able to extract them it is nothing more than a waste of gas, tyres and money.
On an RS or WRX imprezza, or GT legacy it is useful, and does provide more control through more traction, but on anything less IMO its nothing more than marketing hype, a lighter more agile FWD car is often a lot safer, and certianly a lot more predictable if a loss of traction occurs.
Unless provided with the power to put it to use AWD offers no advantage over a good chassis set up and a proper set of tyres.



Ok, thats the end of my rant
(hope it makes sense, and please feel free to point out any glaring gramatical errors).

[Jimster]

The FF stands for FErguson Formula

[JohnnyWash1]

Originally Posted by Chris

Marketing if a funny thing, and is mostly BS.
But there are supposed to be a few fundamental differences in TRADITIONAL 4WD and AWD.
4WD is a part time system, if it isnt part time, its not a 'real' 4WD system. It uses a transfer case, that, when engaged, splits the power by a certain, fixed ratio between the front and rear tires (usually 50-50) Well, from how I understand, it is just a locking differential, so, it makes the same amount of rotations of the driveshaft go to each axle. So, if the front wheels are on ice, and the back wheels are nearly locked, more actual power is being sent to the rear wheels, and both the front and back spin at the same rate. (ie, the rear wheels are exerting a force of 10000newtons, the fronts, only 50 newtons).
A 4WD system is usually left in 2WD, to avoid wear on the transfer case, and possible, minor handling issues.

AWD, on the other hand, is a full time system, with power to wheels changing all the time. The power goes to a transfer case (which will usually be an open or limited slip differential, or a fancy clutch or hydralic system), from there to the front and rear axles, which will have usually an open or limited slip differential, or something fancier.
This works better for things like casual rough weather driving, since its always on.
For real offroad situations, its not as good, there is too much slip in the system, wheels with traction wont get as much power. Still, a good AWD system can be adequate for most cottaging adventures, with tires playing a pretty big role.

Of course, the perfect off road system is totally unpractical for normal use; a locking diff, and locking front and rear ends. Try this for normal driving, fully locked, and you'll end up breaking things, besides handling being terrible.
(note, most factory 'locking' diffs arent lockers, they're limited slips)

So, if you do real offroading, a 4WD system is better, for everyday use, AWD is better, plus, it provides AWD when you might not be expecting to need it, and in a 4WD vehicle, you'd be in 2WD.

This is exactly what my thoughts are on the issue. Well put.



Moppie--Thanks for the info. It certainly is a spin on the issue that I never considered.


Jon

[Moppie]

Originally Posted by Jimster

The FF stands for FErguson Formula

Cheers!


JohnnyWash1 your welcome
Im just glad somebody took the time to read it.