Subaru Automatic AWD isn't really, in most models

[TransFixed]

The Suburu Auto AWD is not the same as the Honda and should not be
compared. The Subuaru system is a proactive system. I see little or no
disadvantage with the Auto AWD when compared to the manual AWD. It is
a proactive system. I have tested this out, and it is very difficult
if not impossible to generate wheel spin.

Case #1: Raining Day. Flooring gas pedal from a traffic light. The AWD
system automatically shift power to rear wheels to compensate for the
weight transfer. In fact in this case, I think it is better than the
50/50 in the manual system, since the manual system waits to slip
before transfer power!!!!

I think it is very difficult to get a wheel to spin just on a wet
surface if you start from 50-50. Remember, each wheel only needs ~1/2
the traction it requires with FWD or BWD, now. If you have the rear
LSD, you are even better off due to the dynamic weight distribution.

So in this case, the AT tries hard to be about as good as the manual.

Case #2: Ice Storm. Again same as above flooring from a traffic light.
No slippage what so ever. AWD system already compensates for weight
transfer to rear wheels!!!

This example I give to you. But then I can come up with plenty other
examples of real world driving, where it is better to be 50-50 from the
outset during driving (not from a dead stop).

Also, once you are a bit up to speed in the AT, it will basically turn
into FWD until it senses or comes into the next problem situation.
Then the rear kicks in, and if you happen to be in a turn at that time,
you will probably say "Whoa! Where did this come from?".

When it is ~ continuosly slippery, the fluid in the MT will be thick all
the time, so it is pretty much locked, no sudden changes there.

- D.

 

[Paul Pedersen]

TransFixed a écrit :

Think of a toy car with locked center diff. Place the front
wheels on fine sand paper, the back on wet ice. All wheels
will turn at the same rate, the car will move forward. Where
did the torque go? 99.9% magically went to the front. The
back wheels did not do any work.

Ok. I can see what you're saying, though like the rest of
this subject, it'll take me a while to digest it. (I don't
like magic

My apologies for putting your words in doubt.

 

[bilgab]

For what i have read, all AT subaru are now full-time AWD. Some models

Read the above posts carefully. You are dscribing the advanced VTD/VDC
AT AWD in the more expensive models. The cheaper Subarus (including the
FOrester and Impreza) don't have that.

- D.

Actually, most of the above post are wrong. I'm describing the basic
system AT subaru have. VTD and VDC are different things. Subaru really
have an full-time AWD. The belief that the AWD on MT is better is
erroneous. And like other posters said, CRV AWD cannot be compared to
the subaru.

The basic system can only make distribution from 95/5 to 60/40. VTD
allows to do distribution from 95/5 to 5/95. When there is no slippage
VTD give a distribution of 40/60 to be more like a sport car.

VDC on the other hand use the ABS system instead of torsens to
distribute torque lateraly.

That MT AWD is better is a myth.

 

[Edward Hayes]

You are correct bi;gab. Read my post which mirrors your understanding and
the Subaru techs here in the US and Australia. eddie

 

[Alan]

Around here, they usually wind up in ditches or against a tree or telephone
pole.

 

[Etienne]

Etienne wrote:


I think it is very difficult to get a wheel to spin just on a wet
surface if you start from 50-50. Remember, each wheel only needs ~1/2
the traction it requires with FWD or BWD, now. If you have the rear
LSD, you are even better off due to the dynamic weight distribution.

So in this case, the AT tries hard to be about as good as the manual.

I believe LSD only comes in certain models. Yes you are correct that
with a 50/50 it is very hard to get a wheel spin.

 

[John M.]

Also, once you are a bit up to speed in the AT, it will basically turn

into FWD until it senses or comes into the next problem situation.
Then the rear kicks in, and if you happen to be in a turn at that time,
you will probably say "Whoa! Where did this come from?".

Wow... I have an '02 Outback VDC H6... and I can't relate to this situation.
I feel always firmly in control. Never have I felt the need to say "Whoa!
Where did this come from?".
Of course, maybe it's just me, or just my car; however I doubt it.
In any case, my car is not 'basically FWD until it senses a problem'. It's
intelligent AWD that constantly puts the torque where it's needed... no
muss, no fuss.
Regards,
John

 

[Father Guido]

Hi,
Okay, I respect your onw personal opinion. But the gap between MT and
smart AT is narrowing. Some day in the future, most cars won't have MT.
You don't even have to steer it, it'll be all automatic.
With high power micro procesor and AI, why not? Just my personal
opinion. Anyhow, I park my car inside garage at home/work.
Tony

God help us if it runs on M$ Windows.

Father Guido
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
I plan on living forever... so far, so good

 

[Stu Hedith]

Nice research. You got it right.

Funny, when I came here I learned that most americans are unable to drive
stick, and Subaru had to take this fact into consideration as well, since
they want to sell cars on the biggest market, so, from my point of view,
they came up with an obvious solution: make a subaru a honda like, and apply
as much marketing BS as possible, so consumers start spending their $$ on
subarus. But since Subaru in a AWD business, they could not give up the idea
completely, and market their ATs as very advanced to those who listen, but
in fact a few people from this group reported that this (very advanced)
tranny can be vary dangerous on slippery turns, when the back kicks in
causing tremendous oversteering, but who cares, cars must be sold anyway.

On a funny note, I never lock my cars, they are equipped with a natural
anti theft device - an MT. Never had a problem for years.

vlad

The AT tranny is not dangerous. Many factors go into a spin. I had a
'98 GT sedan with the AT that is refferred to here and it was VERY
controllable. Under accel it would send power to the rear and create a
SLIGHT oversteer, helping to point the nose where you want it. If you
don't want it, don't hammer the gas. On dry pavement, you could do some
pretty awesome power slides on highway interchanges. Once you hit the
apex, punch it and the rear would hang out a little and go where you
told it. In the snow it would allow for some control of direction when
the front tires were sliding. The only thing i wished i had on the '98
was a rear LSD. I lit up an inside rear tire a few times starting from
a stop under hard accelleration and turning sharply. VCD may provide
for more traction, but I would prefer the vehicle control. VCD aims to
remove oversteer. I prefer oversteer to understeer any day of the week.
I've lost control of various cars suffering from both and once the
under steer kicks in, there's nothing you can do.

Stu

 

[TransFixed]

Paul Pedersen wrote:

....
-snip
....

At least for the 2004 non-turbo Impreza (and Forester ?)
the gear reductions are the same front and back 4.111
so any torque difference must come from the viscous
coupling in the transfer clutch, which under normal
conditions is mostly disengaged. The 90-10 figures I've
seen look sensible for this condition.

With the transfer clutch fully engaged (locked) the
distribution will be 50-50. An interesting thing here
is that I don't beleive it's possible to spin a rear
wheel without a front wheel also being in the spinning
state.

Another thing, I don't see a transfer clutch as a
replacement for a center differential. There's no
balancing function. When the clutch is disengaged
there is little going to the rear, then as the
clutch closes, there is more and more going to the
rear - but - there is never anything to handle the
difference in wheel speeds front and back and
vehicle handling must go out the window. (Just try
driving a car with a locked center differential).

My personal vote is for 90-10 (if not 100-0) unless
conditions dictate a shift to the rear, which can
go to a max of 50-50.

It would seem that Subaru shies away from numbers
when they talk about the MPT transmission...

Nice research, of course some of us have been frustrated for years by
this jumble of true tidbits and useless marketing speech.

The only thing I would add to the above is that 50:50 for a locked
center only applies in the case of same traction front and back. If the
traction is different, the torque applied is different since the axle
with the most grip will do most of the work.

- D.

 

[TransFixed]

Wow... I have an '02 Outback VDC H6... and I can't relate to this situation.
I feel always firmly in control. Never have I felt the need to say "Whoa!
Where did this come from?".
Of course, maybe it's just me, or just my car; however I doubt it.
In any case, my car is not 'basically FWD until it senses a problem'. It's
intelligent AWD that constantly puts the torque where it's needed... no
muss, no fuss.
Regards,
John

You are absolutely right. You have the better AWD of the two AT AWDs.
We were talking about the cheapo AWD in the lower cost AT Subarus (that
are not VTD/VDC). I should have made that clearer.

- D.

 

[Tony Hwang]

Paul Pedersen wrote:

...
-snip
...


Nice research, of course some of us have been frustrated for years by
this jumble of true tidbits and useless marketing speech.

The only thing I would add to the above is that 50:50 for a locked
center only applies in the case of same traction front and back. If the
traction is different, the torque applied is different since the axle
with the most grip will do most of the work.

- D.

Hi,
You're looking at only mechanical part, there is electronics involved.
Not as simple as one might think.
Tony

 

[Paul Pedersen]

TransFixed writes :

The only thing I would add to the above is that 50:50 for a
locked center only applies in the case of same traction front
and back. If the traction is different, the torque applied
is different since the axle with the most grip will do most
of the work.

I originally thought that it wasn't possible to transfer
more than 50% to the rear, with an MPT automatic. I now
see that if the front is slipping and the transfer clutch
is locked, 100% will go to the rear, so anything in between
is possible, though perhaps hard on the transfer clutch.

I think the misleading description of the MPT automatic
is most harmful to buyers of Foresters. There are no
Foresters with VTD transmissions. If I were buying a
Forester for true AWD and then found out that it's
really only a FWD with (fancy) rear backup, I'd be kind
of peaved. (There are manual Foresters, with true AWD).

A few corrections :

I mentioned that the system didn't have any torque
sensors, only wheel speed sensors (and only front
and back, no left and right). I believe it's possible
to deduce torque :differences: from the speed differences,
though I didn't manage to figure out the formula after
a bit of trying. I'm too rusty, I guess. Figuring
out the actual torque would have to take into account
the power output of the engine, not just the state of
the throttle.

I also said that I wanted balanced AWD during engine
braking to prevent a wheel from locking. After further
review this doesn't really happen. It may feel like a
wheel is locked but it's probably only turning less
fast than the other wheels, (still sliding so little
traction). The wheel may stop moving at some point
but that would only be a particular case. In fact
(if I understand things correctly) the slipping wheel
may end up going backwards, like the other three
wheels are trying to get it to do.

Finally, I said that there wasn't a balancing function
with a transfer clutch, compared to a differential. I
now believe that there is, as long as the clutch is
slipping. Not the same kind of balancing, but probably
effective. With the MPT the front is connected directly
to the engine so the front will always get the same or
more torque as the rear (unless the front is slipping)
but I saw somewhere that the front never turns less than
the rear anyway (not sure about this last bit, I haven't
worked it out).

Thanks again TransFixed for your help in my understanding
of things. It's all quite mind-boggling.

 

[Ned Pike]

Around here, they usually wind up in ditches or against a tree or telephone
pole.




..........................................................................
Unfortunately, that's also to

Up here in Vermont, the first sign of true winter is a Grand Cherokee with
Massachusetts plates upside-down in the Interstate median.

 

[Tony Hwang]

Up here in Vermont, the first sign of true winter is a Grand Cherokee with
Massachusetts plates upside-down in the Interstate median.

Hi,
Some Jeep(SUV) drivers are real dumbass. In the middle of summer, a
woman rolled a Jeep making a turn in the intersection downtown here
knocking down mom and kid waiting at the sidewalk to cross the street.
Does not have to be winter. Go figure.
Tony

 

[Alan]

People drive the SUVs as if they were cars. They are trucks. That's why we
got a subie. Wanted 4/AWD without the rollover risk.

 

[Greg Reed]

Tony Hwang wrote:

Hi,
You're looking at only mechanical part, there is electronics involved.
Not as simple as one might think.
Tony

Actually, in the case of a viscous-coupled differential or just a plain-old
viscous coupling (and I'm not clear myself which Subaru uses to distribute
power between the front and rear axles in its manual transmission cars -- it
sounds like they might use both depending on the application), there are
absolutely no electronics involved at all. The lockup is accomplished
entirely by differences in clutch plate speed heating up the fluid in the
clutch pack, which changes its viscosity.

FWIW, Volkswagen's old "Synchro" system (circa 1986 or so) uses a
non-differential viscous coupling. It has only two shafts going into it --
one from the front differential and one from the actual drivetrain. As long
as the front wheels are turning the same speed as the rear wheels, the unit
is "open" and no torque is transferred to the idling axle. When the viscous
coupling unit experiences a difference in speeds between the axles, it
"locks up", transferring torque to the idle axle. A friend who is a devoted
fan of old VW Synchro Vanagons tells me that lockup of this unit takes less
than a second in that application.

A viscous-coupled differential employs the same concept but between the two
output shafts of the differential -- some wheel speed difference is
tolerated, but too much and the unit locks up. I'm pretty sure that this is
what Subaru employs in the rear differentials that are advertised as
"limited slip" such as on my new Forester XT or on the WRX. But as I stated
earlier, I'm not certain whether manual-transmission Scoobies use a center
differential with viscous-coupled limited slip or a plain old viscous torque
transfer unit, like in the old VW Synchro application. The salespeople to
whom I've talked about it know way less about the functioning of the various
AWD systems currently on the market than I do, and can't tell me any more
about Subaru's systems than what's printed in the brochures. They seem to
neither know nor care how their cars' AWD systems work. All they know is
"the wheels that slip to the wheels that grip" -- a catchy line but not
terribly informative.

To Subaru's credit, they've been in the AWD business since long before it
became sheik. They share this proud heritage with just a few other
companies -- most notably, Audi and Volkswagen. These companies were AWD
when AWD wasn't cool, to paraphrase a particularly annoying song. But when
it comes right down to it, I still think that Audi's Quattro is the best AWD
system available. Simple, cheap, and light as viscous coupling units are,
they just can't hold a candle to the Torsen differential that has become
Audi's trademark. Torsens are instantaneous where viscous units don't
engage until *after* wheel spin is occurring. And Torsens can handle
driving with different output shaft speeds all day long, where viscous units
will lock up and cause potentially serious handling and tire wear problems
if both output shafts are not turning at exactly the same speed (as with
slightly different diameter tires on the front and rear axles).

- Greg

--
1976 Cadillac Fleetwood 9-passenger sedan
(for sale: http://www.dataspire.com/caddy)
1989 Audi 200 Turbo Quattro 5-speed sedan
2000 Oldsmobile Intrigue
2001 Chevy Astro AWD (wife's)
2004 Subaru Forester XT (turbo) 5-speed (coming soon!)

 

[Bobby]

|
| I've been spending a lot of time lately studying Subarus
| and am starting to see clear through the misleading text
| by Subaru and others on the subject of AWD and automatic
| transmissions. Personally I drive a manual but I've been
| so bothered by the incomprehensible descriptions of the
| automatics that I wanted to find out what was really going
| on.
|
| With manual transmissions there isn't much confusion.
| Most if not all AWD manuals use three conventional
| differentials : one to split the power front to back,
| then one at each end to split the power side to side.
|
| There is usually something to block the center differential
| so if one wheel spins power will get sent to the other
| end of the car just the same. Most Subarus use a
| viscous coupling in the center differential which locks
| up if there's too much of a difference between front and
| rear.
|
| My Corolla AWD wagon has an electrically lockable
| center differential which is operated at the push of a
| button (as does the current Subaru STi). A much better
| idea, in my mind, in that the spinning wheel doesn't
| get to dig a hole before the differential locks up.
|
| With automatic transmissions the subject should be as
| simple, but the literature describes things in such a
| was as to make things almost incomprehensible.
|
| The only difference between a manual and an automatic
| should be that the clutch is replaced by a torque
| converter and the gears and shifted automatically.
| An automatic AWD Corolla is like this and the power
| out of the automatic transmission goes to three
| differentials like the manual. The only difference
| is the locking of the center differential is automatic
| if speed differences are detected.
|
| Things are not the same with Subaru automatics. First,
| there are two kinds : the MPT and VTD. The VTD is on
| the higher end models like the WRX and Outback H6.
|
| The VTD is true AWD in that it has a center differential.
| But : the MPT, used in most models, does not have a center
| differential. As far as I can tell power always goes to
| the front unless the system detects a difference between
| wheel speeds (using sensors) at which point it will engage
| a multi-plate clutch (like in a motorcycle) to send power
| to the rear. What Subaru doesn't say is that this will
| only happen in the case that one of the front wheels is
| spinning.
|
| I've seen lots of complaints about the Honda automatic
| CR-V being like this, but I haven't seen anywhere that
| the non VTD Subarus are also like this.
|
| In my mind, then, these automatics are front wheel drive
| vehicles unless some very particular circumstances are
| met.
|
| AWD, in my mind, is much more than something to help
| getting unstuck. It's a matter of balance, both in
| power application and engine braking, with everything
| distributed to all four wheels, each doing 25% of the
| work. There is less chance of a wheel spinning during
| acceleration, or of a wheel locking up if you engine
| break in slippery conditions.
|
| If you read texts by Subaru and Honda on their automatics
| you get the idea that the system is constantly adjusting
| things front to back depending on conditions. Well, it
| may be monitoring things constantly, but it isn't doing
| anything most of the time.
|
| So if you're looking at AWD for safety and fun, either
| go with a manual, or make sure you get an automatic with
| a center differential.
|

Been a lot said on this topic by now... I say who cares! AWD on my 02 OBW
with an automatic tranny works just fine when it counts. While I rarely
take my car to it's limits, when I have it hasn't let me down. If I punch
it from a stop light while turning 90 degree's it has yet to slip (even in
wet conditions). Studded tires are Hell on the roads up here (Alaska) and
when it rains there is an extremely bad hydroplaning problem, but not with
my Subie. When I bought my car (in FWB Florida) I test drove it on the
beach, I couldn't get it stuck in the sand...

60/40 or whatever, my tires seem to grip to what's underneath them period.

 

[Andy Mason]

Tony Hwang wrote:



Actually, in the case of a viscous-coupled differential or just a plain-old
viscous coupling (and I'm not clear myself which Subaru uses to distribute
power between the front and rear axles in its manual transmission cars -- it
sounds like they might use both depending on the application), there are
absolutely no electronics involved at all. The lockup is accomplished
entirely by differences in clutch plate speed heating up the fluid in the
clutch pack, which changes its viscosity.

Tony was referring to the automatic version. You're right that the manual
has no electronics involved. It's a viscous-coupled differential for the
center diff.

I think someone already posted this, but it's really worth the read if
you're interested in AWD systems:

http://home.comcast.net/~eliot_www/awd.html

it comes right down to it, I still think that Audi's Quattro is the best AWD
system available. Simple, cheap, and light as viscous coupling units are,
they just can't hold a candle to the Torsen differential that has become

Remember that you can't assume that Quattro = Torsen anymore. Torsens are
used in Audi Quattro's (and VW 4Motions) with longitudinally mounted
engines. Haldex's are used in Quattro's and 4motions with transverse
engines.

Andy
(perfectly happy with the AWD in my manual WRX...)

 

[Greg Reed]

Andy Mason wrote:

Remember that you can't assume that Quattro = Torsen anymore.
Torsens are used in Audi Quattro's (and VW 4Motions) with
longitudinally mounted engines. Haldex's are used in Quattro's and
4motions with transverse engines.

Andy
(perfectly happy with the AWD in my manual WRX...)

Point taken. I'd actually completely forgotten about the Haldex system,
which I perceive as being used by VAG to implement AWD in platforms
originally designed to be FWD only. The specific arrangement to which I was
referring was the use of a Torsen center diff, as is used in all of Audi's 4
and 6 models, and was used in my old '89 200 sedan, as well as the original
Quattro, and most every other Quattro car that Audi released before about
1998 or so. (One notable exception is the old V8 Quattro Automatic, which
used a computer-locked center diff.)

And while I'm planning to purchase a Subaru that AFAIK doesn't have a Torsen
anywhere in it, I still think that the best AWD system ever commercially
produced was that in the Audi V8 Quattro 5-speed, which had Torsen diffs in
both the center and rear axle locations. The perfect AWD system would have
*three* of 'em. (Note that some of the more powerful FWD cars are now
offering Torsens in front to limit the torque steer that results from
violent front-wheel spin in a FWD car. I've never driven one of these cars,
and the torque steer-limiting effect of a Torsen seems counter-intuitive to
me. I'm trusting Car and Driver magazine's editors that the application
really does work.) I guess I'm just a big fan of the Torsen -- much more so
than of viscous coupled differentials.

- Greg Reed

--
1976 Cadillac Fleetwood 9-passenger sedan
(for sale: http://www.dataspire.com/caddy)
1989 Audi 200 Turbo Quattro 5-speed sedan
2000 Oldsmobile Intrigue
2001 Chevy Astro AWD (wife's)
2004 Subaru Forester XT 5-speed (coming soon!)