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Full time four wheel drive (not to be confused with: part time 4WD ) is a system that powers all four wheels at all times. Each tire gets about 25% of the available torque when the ground is level with a consistant surface. Driver has a choice of a "4-high" (that's your every day setting) and "4-low".

When "4-low" is selected the wheels receive substancially more torque (on a Grand Cherokee its 2.72 times more) than in "4-high" - at the same time the vehicle moves at substancially slower speeds (2.72 times slower on J GC).

The low setting is an advantage for drivers who need to tow and maneuver a heavy trailer etc and for drivers who at one point or another may want to negotiate difficult off-road terrain.


All wheel drive is a system that powers all four wheels of a vehicle at all times as well. Difference to full time 4WD is that a "4-low" setting is not available. Due to the lack of "low range" AWD vehicles are much less capable in off-road settings than 4WD vehicles.



Recently some new "automatic" AWD systems have emerged. Fancy names like "Real Time 4WD" are hiding the fact that they are essentially sophisticated 2WD systems. They should be called part time AWD systems. They cannot claim the same (minimal) safety and traction advantages of full time 4WD. They are much less capable in off-road settings than full time AWD systems and inferior to full time 4WD. However, automatic AWD is becoming more and more sophisticated and offers pretty much everything consumers expect for everyday (pavement) driving.

Here is how they work: During traction loss on the driven axle (could be front or rear) a fully automatic system (hydraulic, mechanical or electronic) routes torque to the axle with traction. This means you have to completely lose traction in 2WD on your driven axle first and then the other axle will take over and try to keep the car moving. So, for a moment you have 4WD (AWD). Doesn't mean much because only two wheels have traction. Once the driven axle regains traction and both axles rotate at the same speed again, the system moves back to 2WD.


Finshed

Since you are on the topic of AWD vs 4WD... I want to post something that Frost has posted elsewhere about the same issue...

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For some bloody reason, people are still very much confused about the rather large differences between All-Wheel-Drive (AWD) and Four-Wheel-Drive (4WD - this includes both part time, full-time, Nissan's ATTESA, Honda's stupid Real Time).

Here's the perfect article by Graeme Fletcher, a respected journalist and wheel-head. You've seen him on the Motoring 2004 series on TSN and his credentials speak for themselves.

The difference between four- and all-wheel drive
By Graeme Fletcher - National Post

Friday, May 07, 2004

The key advantage to driving all four wheels is the added ability it can impart to the vehicle. Rather than having to push 50% of the horsepower and torque through each of the front or rear wheels, the system divides the power among all four. This not only reduces unwanted wheelspin, it improves traction on wet pavement and loose surfaces and, perhaps more importantly, whenever traction is temporarily compromised -- such as encountering debris (sand and the like) or a slick spot (oil or ice) on the road.

This description applies to both four- and all-wheel-drive systems. However, this is where the confusion tends to come into play, simply because the terms are bandied about with little or no regard for the significant differences between one system and another. Four- and all-wheel drive are best differentiated according to whether or not the system has a low-range gear set -- in my book, four-wheel drive does; all-wheel drive does not.

Four-wheel drive is generally used on SUVs and pickup trucks, and can be split into two very different groups -- part-time and full-time. The former is exactly as described -- part-time in that it is to be used only on a slippery surface, which is not very much of the time because engaging it on a dry, high-traction surface can cause damage to the drivetrain.

Locking the centre differential (which happens whenever the system is engaged) prevents the rotational speed differences between the front and rear axles (caused by cornering) from being dissipated and so the drivetrain begins to wind up. Driving a part-time system in a circle on dry pavement when engaged causes the vehicle to buck as it tries to spin off the windup by breaking loose one or more of the wheels.

Part-time systems also entail driver input to activate, which further compromises its effectiveness. For example, most highways are ploughed and free from snow during winter. However, many off-ramps are still slippery and so the part-time system must be activated and deactivated according to the changing conditions. The problem with this is that the action invariably comes too late to be of any real benefit, as all part-time systems have a speed above which they cannot be engaged -- some as low as 40 kilometres an hour, which is just too slow to be of value in the off-ramp scenario.

A full-time four-wheel-drive system can be engaged on a dry surface and usually includes an automatic mode. However, most only drive one set of wheels until they begin to slip, at which point the system automatically begins to transfer some of the power to the other wheels. Typically, these systems are referred to as on-demand systems. While of value on a slippery hill or ploughing through snow, they tend not to add to the dynamic ability of the vehicle. This is what separates the on-demand types from true all-wheel-drive systems.

Consider an on-demand system that only drives the front wheels until they begin to slip. In a corner, the vehicle tends to understeer when the front wheels lose grip. Now, shifting some of the drive rearward momentarily pushes the vehicle further into the understeer condition until the front wheels regain grip. That can be scary.

Conversely, the all-wheel-drive systems employed in the new Subaru Legacy power both the front and rear wheels all the time. In most cases, this means sending more power to one set than the other. Depending upon the model, the manner in which this is accomplished varies -- the system tied to the manual transmission is good (it uses a viscous couple to accomplish the power transfer); the one tied to the automatic box is better -- simply because it is more progressive and proactive, which means more balanced.

In the base Legacy, the system married to the automatic uses an electronically controlled clutch pack to distribute the power between the front and rear wheels. Normally, it sends 60% to the front wheels and 40% to the rear. This brings two advantages: First, the extra weight over the front wheels (about 60% because of the engine and transmission) makes it possible to fire more power through them than to the rear wheels before wheelspin becomes an issue. In essence, the weight bias cancels out the drive bias, giving an effective 50/50 split. If any of the wheels do spin, the centre differential locks to deliver a real-time 50/50 split. The second bit is more about preference than ability, as it allows the car to understeer at the edge of the traction limit, which is less disconcerting than oversteer to most drivers.

The system employed in the range-topping GT is better if you want a truly engaging drive. Under normal circumstances, the system sends 45% of the power to the front wheels and 55% to the rear, which imparts a sportier feel because it is possible to hang the tail out. It can lock the differential to split the power evenly if that's the best strategy. But this is the proactive part -- mat the gas and the system recognizes the urgency and automatically locks the system to prevent the back end from fishtailing. Once up to speed, it relaxes its hold, which allows the driver to hang the rear end out. It only intrudes when the driver steps beyond his ability -- my sobering moment came half way around the Cabot Trail in the midst of a torrential downpour.

Regardless of the type, the Legacy's handling is helped by the fact that all of the systems Subaru employs are symmetrical about the centre line of the car. This balances the weight left to right (many are forced to offset the weight in order to package the system) and allows the use of equal-length drive shafts, which banishes torque steer; this in spite of the GT's 250 pound-feet of torque.

<End of article>

For those of you who've read my other explanations, you'll realise I've been saying exactly what Mr. Fletcher here has just said. I have not tried out nor know much about the system in use for Volvo's AWD systems but from initial research, I hear under normal circumstances, the car will have 99% power to the front 2 wheels. Again, I seriously dislike this idea for the same reasons Mr. Fletcher said. The perfect AWD car for daily driving in my mind, would be a 50-50 final bias (drive AND weight combined). This means that in the case that I DO lose traction on any 2 wheels (front pair or rear pair), I have at least 50% power on the road at THE INSTANT OF TRACTION LOSS. For the system by Volvo, if I lose traction in the rear, no problem, it should have 99% power upfront. But how often do you run into situations where your rear loses traction before the front in normal driving conditions? Rarely. Normally your front goes out (simply because it is the FRONT and your car drives FORWARDS into any territory). So say I run into an ice patch. At the INSTANT I hit the patch, the car has 1% power delivery AT THAT INSTANT. While this may be for only 0.001 seconds or what not, the car still has to respond considerably before 50% of the power is diverted to the rear. Also, by suddenly sending most of the power to the back where it normally is almost never present, we are effectively switching cars on the driver. The car will behave differently and the driver will attempt to compensate which in turn will make the car compensate which in turn will make the driver compensate which in turn will... you get the idea. Even Mr. Fletcher agrees on this.

By having a 50-50 split (final), when I hit an ice patch, at THAT INSTANT, I have 50% power to the rear, which means that the car will feel 'weaker' (in sense of acceleration vs. amount of gas pedal pushed in). Let's assume this perfect AWD car can send up to 99% to the rear, it is still only a +49% increase from normal situations as opposed to the +98% increase by Volvo's system. That is HALF the power that is sent to the rear compared to the Volvo! This means that the sudden extra power in the rear will not affect the driver as greatly as Volvo's system does which goes back to the point of driver-car-driver-car compensation loop.

Generally, I dislike how the AWD name is being haphazardly tagged onto vehicles that really should not be tagged by such a name. I believe Volvo is making a serious mistake in doing so but who am I to argue against the mighty corp?

Anyways, I hope you all learned something. Cuz I'm sick of explaining it to everyone, especially the so-called EVO or WRX / STi experts who don't know shit about AWD and 4WD systems yet can still call themselves experts.

Frost

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Good post, the article hits a lot of things head on. And tell me, it upsets me more and more when I am reading things on these cars wtih their 'AWD' system like that volvo which is 'basically' FWD till the system reacts.

I could not explain any of that better in my own words.

This should be a sticky.

I second the sticky request, shoes the difference between many disputed topics.

Yeah it should definetly be stickified... I know up until Frost set the record straight I thought AWD = 4WD...

Itll get a sticky but im going to move it to the tech as well

you've got to be f**king kidding me. ever wonder why there are almost as many kinds of 4wd systems as their are names for them? marketing. sure, they work differently, but they are all 4wd, they are just named by each manufacturer AFTER they are created. that's the key, all these names and terms are created after the system is made to differentiate it, to make it sound more special. but it's all 4wd.


4wd
4x4
AWD
SHAWD
ATTESA
full time 4wd
symmetrical AWD
quattro
super mega awesome magic traction
ETC. ETC. ETC.

just change a differential style here or there, all the sudden you have an entirely different 4wd system!!! better come up with a new name for it!

it's all BS.

my STi is 4wd, yay. it uses 3 lsd's and is full time, it's still 4wd. you know why? because 4 wheels get drive power! which is exactly what 4wd means. i know, it's crazy.

Ive always been under the impression that 4wd sends the power at a constant rate to the wheels- where awd can send varying amounts of power between the front and rear wheels as needed

yeh, how dare volvo call their FWD system AWD!!!

it's almost as stupid as Nissan calling the ATTESA system AWD or lambo and as far as i know, Porsche, calling their silly RWD systems AWD.

know what i really hate though? torsen and electronic center diffs that sense slip before the tire even begins to actually slip and instantaneously change the torque split! damn reactive crap, it should just be a locked center diff for the best handling!!!


good thing you learned me though.


f**king same old pointless crap, it's pure semantics. we might as well bring up the good old motor/engine debate.

4wd=4wd.

QUOTE (sidewaysgts @ Mar 17 2005, 02:41 PM)

if you need to think that way to fit some sort of need for categorization, then so be it. but the truth is, the correlation of "AWD" systems normally using non locked center differentials is a rather after-the-fact reason.

let me put it this way

1. company makes 4wd system
2. company uses unlocked center diff
3. company calls it AWD
4. there for all AWD systems have unlocked center diff.

4 is where the logical fallacy comes in. there is a term for giving a word for this but i have not been able to think of it. the fact is, there are so many kinds of 4wd systems that to try and lump them into groups is just silly. it's best to just drop all the assumptions and asinine terminology and address them individually based on how each works. all these marketing terms were just created out of thin are, so it's pretty stupid to try and argue the differences of these made up terms as if it meant anything.


-edit. i mean, call it what you want, but don't expect the terminology to be gospel. so there is no point in a "ok this is what all these terms mean, this is how each is different" tread. and damn sure no point in acting like you know something special because you wasted your time be studying marketing terms. if you want to point out the difference of actual systems, fine, but associating the systems with their stupid marketing terms is over the line of logic.

see what you did? you made me double post.

Edit by SidewaysGts: Double post fixed

This post has been edited by sidewaysgts on Mar 17 2005, 05:36 PM

Don't mean to agitate you any further VR1... But just was reading up some articles... Apparently 4WD can be switched to 2WD, is this true?

From about.com:

4 x 4 (4WD) - Describes a vehicle with four-wheel drive. The first figure is the number of wheels. The second is the number of powered wheels.

4 x 2 (2WD) - Refers to a two-wheel drive vehicle with four wheels. The first figure is the number of wheels. The second is the number of powered wheels. With a 4x2, engine power is transmitted to only two wheels, usually the rear.

Part-Time 4WD - Refers to a four-wheel drive system that operates on-demand and drives all four wheels by locking front and rear axles together via a shift lever. It usually includes two speed ranges (Hi and Lo). Part-time 4WD systems must be operated in 2WD mode on dry pavement, as they're designed to be used only in specific situations when extra traction is required.

Full-Time 4WD - Describes a four-wheel-drive system that can be operated continuously on all surfaces. A full-time four-wheel-drive system may include the option of part-time operation (allowing you to shift into 2WD on dry pavement for example), and may or may not have Hi and Lo speed ranges.

Automatic Four-Wheel Drive (A4WD) - This type of drive system automatically engages 4WD as needed. When internal monitors sense differences in individual wheel speeds, indicating that a tire is slipping, then 4WD is automatically engaged.

Shift on the Fly - This type of system allows manual shifting from 2WD to 4WD Hi without coming to a stop. Most systems have a speed limit at which you can engage the system; typically it's under 60 mph.

All-Wheel Drive (AWD) - A full-time single-speed system designed to supply drive power to all four wheels. The percentage of front/rear power delivery varies from system to system.

Again... apologies... I don't want to antagonize you or anything... I just want to ensure I know what the hell is 4WD and AWD...

This post has been edited by BOZZY on Mar 17 2005, 05:09 PM

Basicly put, part time 4wd lets the driver select the car INTO 4wd mode. If its a manual theres actualy a 2nd stick to control- automatics often have a seperate lever or buttons you can press to engage it.

I wont argue much with you VR because i know exactly what your talking about, either wya you look at it all the wheels are being powered.

i WILL ask you this though, see if you can find a vehicle marketed as awd with a locked center dif Anything with a varying dif in the center from what IVE SEEN so far (i havent done huge research into this) is considered "awd". The ones ive seen as 4wd have always had a locked dif.

Imo just makes things a little easier to go along this basis when your telling someone something about your car

if you need to think that way to fit some sort of need for categorization, then so be it. but the truth is, the correlation of "AWD" systems normally using non locked center differentials is a rather after-the-fact reason.

let me put it this way

1. company makes 4wd system
2. company uses unlocked center diff
3. company calls it AWD
4. there for all AWD systems have unlocked center diff.

4 is where the logical fallacy comes in. there is a term for giving a word for this but i have not been able to think of it. the fact is, there are so many kinds of 4wd systems that to try and lump them into groups is just silly. it's best to just drop all the assumptions and asinine terminology and address them individually based on how each works. all these marketing terms were just created out of thin are, so it's pretty stupid to try and argue the differences of these made up terms as if it meant anything.


-edit. i mean, call it what you want, but don't expect the terminology to be gospel. so there is no point in a "ok this is what all these terms mean, this is how each is different" tread. and damn sure no point in acting like you know something special because you wasted your time be studying marketing terms. if you want to point out the difference of actual systems, fine, but associating the systems with their stupid marketing terms is over the line of logic.

see what you did? you made me double post.

Edit by SidewaysGts: Double post fixed

I don't like how Nissan calls their ATTESSA an AWD system either. ALL WHEEL DRIVE as the name implies, means all wheels driving at any given point. If the thing is RWD until traction is lost, then it isn't all wheel powered all the time is it? It's just a Full time 4WD system.

It's not semantics. It's downright misleading by the marketing people. If I sell you a V8 engine that only fires 4 of it's cylinders most of the time until it requires more power, is it really a plain old V8?

I've driven clunky old regular 4WDs that required me be at a stop, change the system manually with the shifter and then slowly gas to get out of whatever trouble I was in (usually stuck in sand since it was the desert we were in). Once I got out of trouble though, I HAD to slap it back into normal driving or else I run the risk of really blowing the tranny or the driveshaft. I forgot once and when you turn the B*tch, it JUMPS and HOPS. Learnt my lesson well.

Never had the same problems with AWD systems though.

Frost

This post has been edited by Frost on Mar 17 2005, 05:51 PM

alright good to know!

thanks i was a bit confused

Itd still be a v8 imo, just a really advanced one

Just like i consider the attessa system to be awd, just a very advanced version of it. Its either locked in the center, or its not. No need to over complicate matters

I used to use 2wd/4wd in my brumby before the Sti conversion. 4wd and awd are different. . Reason being as a 4wd Cannot be driven on dry roads or any road infact without putting great strane on the Gear box.

Here's some things copied from a website

4WD refers to part time systems, which run in 2WD on pavement, and
on which you only engage the other axle (mostly front axle, but there are
exceptions) when extra traction/stability is needed. Most (but not
all) of these are heavy offroad vehicles with a split gear T-case
(high/low range). Most (but not all) have a separate frame. Most (but
not all) have solid axles.

Full Time 4WD [RAV4] are those systems which send torque to all
wheels all the time, without user interference or axle-engaging
automagic systems to achieve that. *Additional* user interference
(center diff lock as the most common [RAV4 5sp manual]) and
*additional* automagic systems (viscous LSD on center diff mostly
[RAV4 auto]) can be present. No real distinction between road-going
vehicles and heavy offroad vehicles; both often have full time 4wd
(but again only the latter will have a split gear T-case).


AWD (All Wheel Drive) is the least defined category; often it includes
the full time 4wd category, but I tend to define it more strictly as
those vehicles that *only* send (a significant amount of) torque to
the other axle (mostly rear axles, only a few front axles) *after*
slip occurs. This behaviour is in contrast to full time, where all
wheels get torque all the time, and at least with a fairly even
balanced split (50/50% up to 33/66%, but much more bias than that
makes it rather AWD than full-time.




And More

4WD = Low range and High Range gearing
AWD = Only high range gearing

Part-time 4WD: No centre differential. Cannot be used on dry/wet, semi-slippery roads due to the lack of the centre differential. When activated, both front and rear axles are physically locked to each other and have to spin at the same rate. This becomes a problem when turning on sufficiently high friction surfaces. Examples: Suzuki SUVs, most 4WD pickup trucks, cheaper SUVs.

Permanent 4WD:. No two wheel drive mode. System is equipped with a centre differential, and hence is safe to use on all surfaces. All four wheels are powered all of the time (usually 50/50 front and rear axles). This is arguably the best system since the torque split ratio does not change and is the most predictable. All wheels "help out" all of the time and this stabilises the vehicle + improves handling. With the extra two drive wheels, the vehicle has twice the amount of traction all of the time (even in no-slip conditions) vs. a 2WD vehicle. Examples: MB M-class SUV, the Range/Land Rovers.

Full-time 4WD: Basically permanent 4WD but with a 2WD mode. This was born out of customer demand (for a 2WD mode). Examples: Toyota Sequoia, Mitsubishi Montero.

Permanent AWD: Basically permanent 4WD but without low range gearing. Examples include the Audi Quattro AWD system, the MB's 4-matic AWD system, Subaru's manual transmission AWD system.

Full-time AWD: System is active at all times, however in most cases, the one set of wheels (usually the rears) only receive 5-10% of the engine's power unless slippage occurs. At that point, power is progressively transfered to the opposite axle to help out. Some systems can transfer power to the rear upon acceleration to improve traction. However, they revert to 2WD mode when coasting

This is a very informative thread. Good thing it's stickied.

yes it is still a V8

does it have 8 cyls? yes
is it in a v config? yes

so it's a v8

dodge started doing that already; and NO ONE is B*tching

This post has been edited by InitialN00b on Mar 17 2005, 09:58 PM

^ I wonder if thats available on the SRT-10. Should save a ton at the gas station, no?

I'm pretty sure as they develop the technology further, it'll be available in most V8 and V10 engines.

It's actually not that ground breaking. why it took them this long to develop, who knows.

All of you keep on forgetting on Quadtec!!!!! Anyways, thanks for the info.

yes it is still a V8

does it have 8 cyls? yes
is it in a v config? yes

so it's a v8

dodge started doing that already; and NO ONE is B*tching

Yeah but I said it is just a plain old v8? It's an ADVANCED v8. That's the point. AWD is a much more advanced system than classic 4WD ever was.

Frost

I thought ur overdone v8 was how the attessa wasnt "awd" to you- when say to me it is.

Here is a link to the Subaru Website.

http://www.subaru.com/allwheeldrive/ver2005/index.jsp
Click the 'What is the difference', and it will explain the differences between the 5 versions/aspects of AWD that subaru offers.

This post has been edited by DGoReck on Mar 18 2005, 05:15 AM

I've seen that site before - Hey Dgoreck, which one of those do our cars have?

I'm guessing continuous?

Again, I go back to the definition of AWD being ALL wheel drive. My understanding of this is that all wheels are powered all the time.

The Attessa system, as fancy as it is, is no different in its working idea than say Honda's full time 4WD system. Point is that it doesn't power all the wheels all the time.

I'm more against people who don't differentiate between 4WD (classic systems that involve you to manually switch to that mode) and AWD systems. The newer "on-the-fly" systems and full time 4WD systems are still fairly new ground to me (since I've never really driven one on true off road). My experiences lies with Toyota Landcruisers (pre 1994) on sand dunes and the Subaru Legacy GT (1997 and 2005) on snow and dry tarmac.

The v8 example was to highlight the clear differences between the original and the considerably newer v8's that are hitting up the market from Dodge. While, like InitialN00b said, they do have 8 cylinders in V orientation they are NOT classic v8's because they have evolved so much more than their original forefathers. Same thing with AWD and classic 4WD. Audi took 4WD and evolved it into a new breed of drivetrain so that you could have the advantages of 4WD (most of them) without the hindrances of 4WD.

In the essence, the chimp became a man.

Frost