4WD and AWD systems explained

paisan

The torque split on the 4EAT found in the 09 Forester would likely be the same as the ones found in the other vehicles up to this point. The addition of VDC only controls the throttle cut and ABLS that is applied laterally. My educated take on this is that it still has an 80/20 to 20/80 split because it doesn't include the VTD, the VTD is what gives it the 45/55 initial split found in the 5EATs.

-mike

dcm61

I think the confusion may lie in the fact that this is the first year ('08 Legacy/Outback/Impreza, '09 Forester) that VDC was offered w/o VTD.

All previous models with VDC also had VTD, but there were some VTD models that did not include VDC.

paisan

Actually, the Spec B has had VDC since 2006, but there is no VTD on it. It is a 6MT w/rear mechanical LSD.

-mike

rsholland

I e-mailed Mike McHale, Subaru's Director of Corporate Communications regarding the ongoing Subaru AWD front/rear power split debate. Here's his response:

The AWD system on cars with the base automatic is truly continuously
variable. There is no gear set that locks in a specific split, as
there is on the VTD or manual transmission cars. Therefore the front
to rear split is based upon the lockup percentage of the transfer
clutch, which could be as diverse as 90/10 or up to 50/50 depending
on power input/grip needs.

Now since Mr. McHale is responsible for any information that goes out to the public regarding Subaru products, he should certainly know what he's talking about on this matter.

...And yes, I did get his permission to use his name here.

Bob

psychogun

Now that's more like it.
Thank you for obtaining that official statement Bob!
Technically speaking, it now certainly appears that the Forester has the more advance AWD system than Mitsubishi decided to install in the Outlander (much as I am disappointed to admit it :-P ).

However, as has been suggested by ateixeira, I would still like to see these two vehicles face off in a controlled testing environment, using the same tire setup.

Or... if an owner of each car could be convinced to buy the same type of tires and go run some trails...

dodo2

Technically speaking, it now certainly appears that the Forester has the more advance AWD system than Mitsubishi decided to install in the Outlander (much as I am disappointed to admit it ).

Why is that? Mitsubishi claims that the F/R torque power split could go up to 40/60 in 4WD Lock mode and the power allocation is automatically split based on the similar criteria.
In the light of what I consider Subaru official information from Bob's post, at least the Forester's AWD cannot be considered superior based on the paper F/R power distribution.

A real world, true test would be needed in my opinion to determine which system performs better. Until then, any assumption would be pure speculation from either side.

ateixeira

I was the one that originally called for a ramp re-test now that the 2009s have arrived.

I think we finally found something everyone can agree on. LOL

The AWD system is the same as the one in that video (it was a US-spec 2008 Forester X, automatic), but traction control was added and it would be worthwhile to see if it can transfer enough power side-to-side so that one wheel could power the vehicle up the ramp.

Besides the addition of traction control, the 2009 Forester also has a lot more ground clearance. Most of the time when you get stuck it's because you have high-centered, so ground clearance plays the biggest role.

If the old model didn't have enough, well, that's been addressed for 2009.

Keep in mind Car & Driver said the Outlander has the worst departure angle among all the 9 crossovers it tested, and that's an objective measure.

rsholland

Just keep in mind this is the case only for Subaru automatics without VDT. VDT-equipped automatics have a default front/rear power split of 45/55.

All manuals, except the STI have a 50/50 default front/rear power split. The STI AWD is driver controlled, with a default setting of 41/59 front/rear, and can be adjusted in six segments on up to a 50/50 lock.

Here's a link from Subaru's PerformanceDrive magazine explaining the STI's AWD set up, and the various settings, and when to use them.

http://www.driveperformancesubaru.com/version5_1/blueprint.asp

Finally VDC has no bearing on the power front/rear split.

Bob

dodo2

I agree that the ground clearance plays a crucial role in the off-road conditions, but the comparo you keep referring to - C/D, does not seem to take that into account. The Outlander has the highest ground clearance at 8.5 inches out of all other Japanese SUVs in the test (Forester not included), yet the C/D considers than the RAV4 (7.5") or the CRV (7.3") are better "off-roaders" LOL. I guess they base their conclusion on the approach and departure angles which are less relevant for what any of these CUVs are designed for.
I guess my point is that I wouldn't use these type of comparisons as a serious argument.

The 2009 Forester however has slightly higher ground clearance at 8.7" (2.5X) respectively 8.9" (XT). The 0.2" could make a difference in a very specific test at the most, but still you cannot say only from that small difference in ground clearance that the Forester is better "off-roader" than the Outlander, unless you run a full battery of tests.

Also, any reference to the 2008 Forester in a 2009 Forester discussion is not relevant since they are totally different vehicles.

dodo2

Just keep in mind this is the case only for Subaru automatics without VDT
......

Finally VDC has no bearing on the power front/rear split.

Please correct me if I'm wrong, but this is where the 2009 Forester 4AT falls in.

rsholland

You're correct; same with the Impreza and NA 2.5 Legacys and Outbacks.

Bob

ateixeira

It's just one factor out of many. Break over angle, approach angle, departure angle, ground clearance, articulation/suspension travel, and the primary one - tire choice. Plus AWD/4WD, of course.

The original Forester only had 7.5" so they've improved that a lot.

I'm sure the new Outlander has more ground clearance than the old one did, too.

dodo2

I wonder how many CRV, RAV4, Outlander, Rogue, Forester owner actually check for the departure/approach angle when they make their purchase decision. These numbers aren't even posted by the manufacturers in their respective specifications.
The ground clearance is the only "off-road" parameter that shows up in the specs.

ateixeira

I'm sure less than 5%. Probably more like 1%.

Most folks just want to sit up high and be able to go over speed bumps in their 'hood without having to slow down too much. And to be able to buy milk when the snow storm starts.

Having said that, Subarus, especially in other markets like Australia, are used far more aggressively than the average US consumer.

dodo2

Exactly. So why would that even be a consideration for a relevant comparo? What really matters for these vehicles is how capable they are to get you out of a slippery situation (ice/snow) or up to a rutted hill, eventually slippery, but they don't test that at all therefore they are meaningless from this stand point.

In regards to the other markets specifics, the same goes for the Mitsubishi vehicles. They are know for their off-road capabilities - the Outlanders much less than the Pajeros though. But there are different kinds of off-road situations though. I don't think anywhere in the world, the Foresters or Outlanders are used for rock-climbing type of activities where the ground clearance, departure/approach, wheel travel matters.
However, the Pajeros are, but they are a different bread of vehicles and they can go where no Forester (or Subaru) or Outlander can dream of going.

ateixeira

Well, you have to test the extremes to determine what a system's capabilities are.

In moderate use you probably will not observe any difference between the most capable AWD system and the least. So they push them a bit.

Yes, C&D got the Jeep stuck in the mud, but they were playing around, and didn't try taking any of the other vehicles there. That wasn't really part of their comparison evaluation.

paisan

I've said it before and I'll say it again from years and years of off-road experience....

Tires are the #1 off-road asset.
Ground clearance and smoothness of the bottom (ie: running boards, low haning fuel tanks, etc) is the #2 off-road asset.

After that the other factors come into play but a 2wd (rwd at that) with the above will outdrive an AWD vehcile which has hangups and bad tires anyday in off-road, snow, etc.

-mike

chelentano

>> the front to rear split is based upon the lockup percentage of the transfer clutch, which could be as diverse as 90/10 or up to 50/50 depending on power input/grip needs.

You did a good job with emails to Subaru. Finally we can put these myths to rest: the 4-speed auto Subaru Forester transfers only 10% to the rear by default and up to 50% in extreme conditions. Period.

This makes it a part-time AWD system, according to Eliot Lim in his article Intro to AWD Systems: "Subaru has for many years been quietly offering radically different AWD systems in the same car, depending on the transmission choice. The manual transmission Legacies and Imprezas use a full time system that is split 50-50 with viscous couplings for limiting slip. In the automatic transmission versions, however, the system is a part time, computer controlled, automatically engaging system in some models and a full time uneven torque split with computer controlled locking in other models."

As result you can find a bunch of Youtube videos were Forester can’t climb up hill, or stuck and needs a tow track. You can’t find this kind of Outlander videos: the Outlander 4WD Lock is a true full-time system both on paper and in real life. The armature videos show impressive Outlander performance cruising through an open field of one foot snow or through a russian mud. video links
.

>> Just keep in mind this is the case only for Subaru automatics without VDT. VDT-equipped automatics have a default front/rear power split of 45/55.

Sure, Subaru VDT-equipped automatics are very capable true full-time systems with power split of 45/55. But Mitsubishi equipped with Super Select II system are even more capable: according to chief Audi chassis engineer Eliot Lim in his NY Times article, Mitsu Super Select II can distribute up to 100% to either axle. This system is superior not only on paper, but also in real life: the Super Select II equipped Pajero has won 7 Dakar rallies in a row – spectacular performance in Sahara desert.

Of course, such mastery calls for some serious hardware, so the Pajero's SS4-II drivetrain boasts not one, but three four-wheel drive modes. Quote “You can change from full-time, fuel-efficient two-wheel drive to 4H, ideal when the road suddenly becomes slippery. When the going gets tough, simply lock the center differential (4HLc) with power equally distributed between both axles, and for maximum off-road ability select 4LLc to virtually double effective engine breaking in any gear. SS4-II works in conjunction with both Mitsubishi's highly acclaimed Active Stability and Traction Control system, ensuring optimum grip in all conditions, and EBAC which automatically engages in extreme downhill off-road.“ The SS4-II is available on both manual and automatic Pajero.

stever

Tires are the #1 off-road asset.

I'd put the driver right up there too.

I bet a pro could take my minivan further into the boonies than I could get my Outback (or my old CJ-5).

And I'm sure a pro could lap me driving my minivan on the track while I was trying not to spin out a GT. :shades:

rsholland

No way is it a part-time AWD. There is always some power being sent to all wheels, all the time. Therefore it's a full-time AWD, not part-time AWD.

This is from SOA also (not Mike McHale), in case you missed my posting:

You are welcome. I can answer part of your question; but, not the maximum percentage to any given axle. It will NEVER be 0/100 or 100/0. Each wheel/axle will always have some power. It is never that all power is to either axle. Hope this helps!

For it to be part-time, one of the axles must not get any power at some point. That's not the case with any Subaru.

Bob

ateixeira

Forester transfers only 10% to the rear by default

That's not what they said at all.

Read these again:

The AWD system on cars with the base automatic is truly continuously
variable. There is no gear set that locks in a specific split

The AWD System on our automatic transmission models not equipped with VDC or VTD do not have a default power split. For these vehicles, the power split is always fluctuating due to conditions. This is why we do not list a default setting in any of marketing brochures, Web site, etc.

Each wheel/axle will always have some power

How someone can read those and conclude there is a specific 90/10 default power split and that it's a part-time system is beyond me.

according to chief Audi chassis engineer Eliot Lim in his NY Times article

Yeah, according to him all Audis have the same AWD system. Remember the "Audi - all" part.

So this is an Audi engineer who does not know that Audi's Haldex is different than Audi's Torsen AWD systems.

What a complete imbecile!

kdshapiro

http://www.wheels.ca/article/27672

stever

That reminds me of the time Top Gear took a Land Rover Discovery to the top of a mountain in Scotland. They keep having to dig and winch it out of peat bogs every 10 minutes,

kdshapiro

There are really some unbelievable videos about people who take their trail capable cruisers off-road. Some people should be watching off-roading rather than doing it. :shades

chelentano

Sure, technically speaking it is full-time. And at 10% rear torque it's grandma's full-time.

chelentano

It says in the article though that he "suddenly hit something hard", though it's good find. I can counter that picture with these videos:

http://youtube.com/watch?v=yDa943LFz04
http://www.youtube.com/watch?v=PViXtykEzp0&NR=1
http://youtube.com/watch?v=Lh9ioh4aZfI
http://youtube.com/watch?v=fsIr4sIOVQo

Outback's humiliating performance on ice. This is not a marketing simulation at Subaru dealership Ateixeira keeps showing. It's a real thing:
http://www.youtube.com/watch?v=guTQWkpPFa4
http://www.youtube.com/watch?v=Nmrr60SwWKY&NR=1

And again, it just can't get it up:
http://youtube.com/watch?v=g6H3IOtE6Q8

paisan

I raced a 1996 Impreza L with a 4EAT which is very similar to the unit found in the current generation Forester. It may have been able to do 90/10 but at no time during my road racing of it, did the AWD system fail to provide grip to the front or rear when needed. So we can go around in circles about torque splits, reaction times, etc but there is no substitue for real world experience with a particular vehicle.

-mike

chelentano

>> “The AWD System on our automatic transmission models not equipped with VDC or VTD do not have a default power split. For these vehicles, the power split is always fluctuating due to conditions. This is why we do not list a default setting in any of marketing brochures, Web site, etc.”
>> How someone can read those and conclude there is a specific 90/10 default power split and that it's a part-time system is beyond me.
.

That statement is about Subaru NOT equipped with VDC or VTD. Otherwise, for non-VTD base automatic read this part of Rsholland’s email:

“I e-mailed Mike McHale, Subaru's Director of Corporate Communications regarding the ongoing Subaru AWD front/rear power split debate. Here's his response:
The AWD system on cars with the base automatic is truly continuously variable. There is no gear set that locks in a specific split, as there is on the VTD or manual transmission cars. Therefore the front to rear split is based upon the lockup percentage of the transfer clutch, which could be as diverse as 90/10 or up to 50/50 depending on power input/grip needs.

Now since Mr. McHale is responsible for any information that goes out to the public regarding Subaru products, he should certainly know what he's talking about on this matter.

...And yes, I did get his permission to use his name here.”

chelentano

>> we can go around in circles about torque splits, reaction times, etc but there is no substitue for real world experience with a particular vehicle.

You certainly right, that's why REAL WORLD videos I posted speak for them self. As you say, there is no substitute.

paisan

This current generation 4EAT is the first with VDC w/o VTD, the last gen WRX had VTD but no VDC.

The VDC does not effect the F/R torque split at all, it only manages the Left/Right torque split so is irrelivent in terms of a F/R discussion.

-mike

paisan

You certainly right, that's why REAL WORLD videos I posted speak for them self. As you say, there is no substitute.

I said nothing about Videos. Unless of course you were the one driving in those videos.

As race driver and track instructor, I can control my car in a lot of different ways. I can drive my car in a manner that will skew it to appear to be out of control when in fact it is in control or in control when it is not in control. Slight throttle inputs, left foot braking, steering wheel control, momentum, braking point, etc. All can be controlled by a good driver to skew a video in any way they want it to appear. That is why I often do not put much weight into videos, test drives or anything that I have not personally tested.

So I say, go out to your Subaru Dealers and Mistu Dealers the next time it snows, and take em for test drives. See how they handle and if you like it, buy it, if you don't then don't. It's that simple.

-mike

chelentano

>> The VDC does not effect the F/R torque split at all, it only manages the Left/Right torque split

That's fine with me, but Subaru Director of Corporate Communications Mike McHale still says that "The AWD system on cars with the base automatic ..... could be as diverse as 90/10 or up to 50/50".

So his statement is completely consistent with split numbers form NT Times article, Wikipedia, Cars101.com, etc.

paisan

But he specifically states in that statement that there is NO DEFAULT TORQUE SPLIT. So whoever is assuming that it's 90/10 is wrong. It could be 50/50 default under certain conditions (throttle position, weight sensor, wheel speed sensors, etc)

Are we going to keep going around in circles?

-mike

chelentano

You say yourself, that it "could be 50/50 default under certain conditions". You can't have it both ways DEFAULT and UNDER CERTAIN CONDITIONS.

The actual meaning of "certain conditions" directly contradicts to the meaning of "default". Also he says "up to 50/50", specifically defining the upper range under certain condition. All other publications, like Wikipedia, NY Times and cars101.com also specifically define front bias and upper 50/50 split for extreme conditions, in case someone wants to misinterpret.

At least 80/20 - 20/80 split numbers are out of question. :--)

rsholland

My guess—and it just a guess—is that because the front/rear power split is constantly changing, that the 90/10 front/rear "situation" occurs under the least stressful kind of driving, such as when the car is coasting with no throttle being applied. Under other driving situations, accelerating, braking, cornering, going up hills, etc., that more power is sent to the rear wheels. How much? Anywhere up to 50 percent depending on the need.

Again—just a guess—I would assume that as more power is applied by the driver, more power is transfered towards the rear. That's how the Honda real-Time 4WD works; when the driver applies any sort of power; starting from a dead stop, passing, going up hills, etc.; it is sent to the rear wheels. I would think that's the case with base Subaru automatic. The difference in "practice" between the Honda and Subaru system is that the Honda has 0% power going to the rear whereas the Subaru has at least 10% power to the rear wheels before any power is applied.

Bob

kdshapiro

It says in the article though that he "suddenly hit something hard", though it's good find. I can counter that picture with these videos

If you believe the Subaru AWD is part-time, by all definitions the Mitsu system is part time since you need to flip a switch to activate it. As far as the "hitting" something hard, it still got stuck.

The reason there aren't a lot of videos of the Mitsu getting stuck, no one in their right mind would take the Mitsu in the same situtations as they would any Subaru because the AWD was (is?) less capable. Whatever you believe about the F/R split is irrelevant as the system performs and performs better than the competition and people have the confidence (or stupidity) to see how good it is and test the thing to the limits.

dodo2

I said nothing about Videos. Unless of course you were the one driving in those videos.

To me, the ultimate test in Forester vs. Outlander AWD capabilities would be to have two test vehicles equipped with proper tires and wheels driven by Kdshapiro respectively Chelentano, on the same test course.

comem47

If you believe the Subaru AWD is part-time, by all definitions the Mitsu system is part time since you need to flip a switch to activate it. As far as the "hitting" something hard, it still got stuck.

When will you ever get over the switch? You can leave the switch in any of the 3 positions for the life of the car and never change it again if it makes you happy. I think the ability to select FWD and eliminate friction is a plus when you are in dry conditions (gas economy). I also suppose you wouldn't want a switch to disable traction control too in a FWD car? (no ability to rock the car with momentum, but rather have the power cut and go no where when stuck in snow). Think of the switch as more flexible and no, sometimes the driver knows better than the car (more flexible, another option).One is not "enabling" with the switch, bur rather "overriding".

ateixeira

That is not what you said.

You wrote this:

the 4-speed auto Subaru Forester transfers only 10% to the rear by default

That directly contradicts this from SoA:

truly continuously variable. There is no gear set that locks in a specific split

Furthermore, if the Outlander defaults to 85/15, that's "nearly part-time" as you would say.

If the Lock mode is only meant for temporary use, that probably means there is no center differential, so it's not truly full time if you think about it.

ateixeira

The bottom line is these needs are very contradictory.

The best vehicles on pavement are lousy off road. You want little body roll, no dive and squat, and firm sidewalls on the tires. For tires you want a low void ratio to get as much rubber on the road as possible. The lower the better from a handling stand point.

Off road, you pretty much want the opposite. You want to maximize articulation, to keep the tires on the ground when it's uneven. Most off roaders add sway bar disconnects, even. Off road tires have massive voids to get traction in the rough stuff. They're the opposite of low - think Sky Jacker.

No one vehicle can do it all, nor should it be expected to.

kdshapiro

When will you ever get over the switch? You can leave the switch in any of the 3 positions for the life of the car and never change it again if it makes you happy.

That is not true. The lock mode is meant for situations where there is wheel slippage. See above posts.

I also suppose you wouldn't want a switch to disable traction control too in a FWD car?

Stability control is a different animal. It can save your bacon. There is no such thing as f/t stability control vs p/t stability control as there is AWD and 4WD systems.

chelentano

>> Furthermore, if the Outlander defaults to 85/15, that's "nearly part-time" as you would say.

Alright, but 85/15 is for Outlander Auto mode, which is similar to Forester AWD, though 15% is 50% more vs. Subaru's 10% default.
.

>> If the Lock mode is only meant for temporary use, that probably means there is no center differential, so it's not truly full time if you think about it.

It's not only meant for temporary use.You can use it for the life of the car, and yes there is center differential on the Outlander.

chelentano

>> When will you ever get over the switch? You can leave the switch in any of the 3 positions for the life of the car and never change it again if it makes you happy.

>>> That is not true. The lock mode is meant for situations where there is wheel slippage. See above posts.
.

No, what Comem47 says is true. You can leave the switch in any of the 3 positions for the life of the car including the Lock mode. Both Auto and Lock mode adjust torque for wheel slippage, it is just the Lock mode delivers 50% more power.

ateixeira

Tell that to C&D. In their comparo they say "none" for center differential for their Outlander.

Also, you're still claiming the Subaru defaults to 90/10, ignoring the e-mail SoA sent to Bob.

There is no default split. It varies constantly.

ateixeira

Explain something to me, though, please.

You keep referring to a NY Times chart, riddled with inaccuracies, written by an Audi engineer who doesn't know the first thing about Audi AWD. So how is he supposed to be an expert on AWD systems from Subaru and Mitsubishi?

He doesn't even know Audi's own AWD, and he supposedly worked for them? This is your source? LOL

Plus, the chart is from 2003 or so. They actually list the RX300 on that chart. I double-checked, the last model year for the RX300 was 2003, which means they stopped making them in late 2002. The chart is older than I thought!

So how, then, is that a reference for the AWD system on a model year 2007+ Mitsubishi Outlander?

Your reference chart is inaccurate, written by a clueless ex-Audi employee (maybe he got fired?), and does not even refer to 2007+ model anyway.

Did he have a time machine, travel forward through time, evaluate a 2007 Outlander, then go back in time and fill out that chart in 2003?

The reference is completely, totally invalid.

chelentano

I agree, base Subaru automatic has a very similar AWD to Honda's on-demand part-time 4WD system.

kdshapiro

And also similiar to the Outlander. I guess it can safely be said all AWD systems are similiar except where they are different. :confuse.

kdshapiro

At least 80/20 - 20/80 split numbers are out of question. :--)

I don't think so. It seems as 80/20-20/80 splits are very much possible.

kdshapiro

No, what Comem47 says is true.

Someone posted excerpt from owners manual. Even the owners manual states lock mode is for temporary use on gravel, mud or snow. Leads me to believe the AWD life can be shortened by constant use in lock mode.

paisan

At least 80/20 - 20/80 split numbers are out of question. :--)

I don't think so. It seems as 80/20-20/80 splits are very much possible.

For the 2009 models yes, however, I stand by what Subaru Engineering told me for previous versions from 1988-2000

-mike