True AWD

[Daya]

I took my Forester to a shop once to check for a nail on my rear tire. I
watched the mechanic as he was turning the rear tire of the jacked car and
looked nails. I saw the front tire turning too.

People said lots of the cars on the road are not TRUE AWD cars. Even the
expensive Murano is a FWD.

I'm wondering, besides Subaru and Audi, which cars on the road out there are
really TRUE AWD cars.

 

[330xi]

BMW xdrive.

(e-mail address removed)

 

[Bonehenge]

I'm wondering, besides Subaru and Audi, which cars on the road out there are
really TRUE AWD cars.

Not all Subaru's are. Manual tranny versions are, many automatics
are, but some automatics are just like the Murano.

 

[Alan]

Not all Subaru's are. Manual tranny versions are, many automatics
are, but some automatics are just like the Murano.

Could you elaborate?

 

[Bonehenge]

Could you elaborate?

The best layman's terms explanation I've seen:
<http://www.cartalk.com/content/columns/Archive/2000/October/01.html>

The key theory is that the manual transmission version is using a
50/50 power split, front to rear, much of the time. The automatic
sends most (90/10 has been mentioned elsewhere, but I'm not sure of
the exact numbers) of the power to the front wheels when the car is on
a good footing.

Barry

 

[jabario]

Manual subarus have a 50/50 power split f/r. Automatics are 90/10 f/r
with the ability to vary it based on conditions and slippage.
Doesnt mean its not AWD.

 

[Alan]

Manual subarus have a 50/50 power split f/r. Automatics are 90/10 f/r
with the ability to vary it based on conditions and slippage.
Doesnt mean its not AWD.

You guys are not up-to-date. The 90/10 business went away quite some time
ago. There are three AWD systems now, one for manual, and two for automatic.
None are 90/10.

 

[Sparky Polastri]

You guys are not up-to-date. The 90/10 business went away quite some time
ago. There are three AWD systems now, one for manual, and two for
automatic.
None are 90/10.

Well... mine was 90/10 when I bought it. SO unless the little Subaru
Upgrade Fairies snuck in my garage and replaced my tranny and AWD some warm
summer night, I suspect it's still 90/10.

NEW Subarus might have something different. But a lot of them on the road
are still operating on the old stuff.

Subaru's web site has a lot of great info that is fairly in-depth about it.
I suggest starting there to find out what the new cars have on them.

 

[Mike]

I think the new ones (WRX, anyway) are around 70/30 to 60/40.... the STi is
driver variable between 50/50 to 70/30... don't quote me on those numbers
though.

 

[y_p_w]

You guys are not up-to-date. The 90/10 business went away quite some time
ago. There are three AWD systems now, one for manual, and two for automatic.
None are 90/10.

Some of the Subaru automatic tranny AWD systems use an electronically
controlled transfer case rather than a mechanical center differential.
This was mentioned in the Forester tire replacement thread a few days
ago.

 

[John A. Mason]

The best layman's terms explanation I've seen:
<http://www.cartalk.com/content/columns/Archive/2000/October/01.html>

The key theory is that the manual transmission version is using a
50/50 power split, front to rear, much of the time. The automatic
sends most (90/10 has been mentioned elsewhere, but I'm not sure of
the exact numbers) of the power to the front wheels when the car is on
a good footing.

Barry

Here we go again <sigh>. My '02 VDC H6 splits 54.55 rear and 45.45 under
normal driving conditions with friction between front and rear equal (this
comes directly from the Subaru technical manual).
John

 

[Edward Hayes]

Subaru SOA and Subaru of Altrailia says my 2000 Forester 4EAT has a
default ratio of 60 front and 40 rear. 90/10 went out of style about
12 years ago.

 

[Dominic Richens]

Not all Subaru's are. Manual tranny versions are, many automatics
are, but some automatics are just like the Murano.

More to the point of the OP question, with the 5MT Subaru transmissions, the
front and rear drive axels are actually physically connected all the time,
through a viscouse coupler. So yes, even with the ignition off, if you turn
one wheel the other three turn aswell.

 

[JD]

I think the new ones (WRX, anyway) are around 70/30 to 60/40.... the STi is
driver variable between 50/50 to 70/30... don't quote me on those numbers
though.

The WRX is still 50/50 with an LVCD. The STi is 65/35 Rear bias. The DCCD
selects how open the differential is. It doesn't actually vary the torque
split I can assure you (drive it on ice and you will KNOW it is not a 50/50
split). However, with the DCCD set to LOCK, the differential will lock up
and does not need to detect wheel-spin before locking. With it set in AUTO,
it will lock up the centre diff when it detects wheel-slip. However, it is
pretty slow to do it on ice. I leave it in LOCK if the roads are really
bad, or put it in LOCK to start, and switch it to AUTO to cruise.

 

[Aaron M]

My US MY 2000 (Japanese MY 1999) Impreza 2.5 RS automatic has a 90/10
split with a limited slip rear differential. It makes for some
interesting driving in the winter if you don't add some weight to the
rear end. Thank god the first snow I drove it on was in an empty
parking lot.

Nothing like having most of the power transfered to the rear and then to
just one tire. I've carried 50 lbs of sand in the trunk during the
winter ever since.

I believe with the Impreza redesign the automatics went to 55/45.

 

[Rob Munach]

More to the point of the OP question, with the 5MT Subaru transmissions, the
front and rear drive axels are actually physically connected all the time,
through a viscouse coupler. So yes, even with the ignition off, if you turn
one wheel the other three turn aswell.

Actually, they are connected with a geared differential with a viscous
coupling in parallel to minimize slip.

 

[Dominic Richens]

Actually, they are connected with a geared differential with a viscous
coupling in parallel to minimize slip.

Yes, but it is the VC that makes the two shafts turn together. With no VC,
if the transmission is in neutral, then the differential just spins and the
front shaft doesn't turn. If the transmission is in gear, I think the front
wheels will turn in the opposite direction!

 

[Rob Munach]

Yes, but it is the VC that makes the two shafts turn together. With no VC,
if the transmission is in neutral, then the differential just spins and the
front shaft doesn't turn. If the transmission is in gear, I think the front
wheels will turn in the opposite direction!

Actually, you are partially correct. A typical Forester does not have
LSD's in the front of rear. Assuming all wheels are off the ground, if
you turn one back wheel, the other back wheel will turn backwards and
the drive shaft wont spin. The same goes for the front wheels. However,
if you rotate the rear driveshaft, the front driveshaft will rotate
backwards with a center diff. and no viscous copuling and will rotate
the same direction as the rear driveshaft with a viscous coupling or a
viscous coupling in parallel with a center diff.

 

[David]

Actually, you are partially correct. A typical Forester does not have
LSD's in the front of rear.

For US models, I think X has an open diff in back, while XS & XT have a rear LS diff.

 

[k. ote]

The WRX is still 50/50 with an LVCD. The STi is 65/35 Rear bias. The
DCCD selects how open the differential is. It doesn't actually vary the
torque split I can assure you (drive it on ice and you will KNOW it is not
a 50/50 split). However, with the DCCD set to LOCK, the differential will
lock up and does not need to detect wheel-spin before locking. With it
set in AUTO, it will lock up the centre diff when it detects wheel-slip.
However, it is pretty slow to do it on ice. I leave it in LOCK if the
roads are really bad, or put it in LOCK to start, and switch it to AUTO to
cruise.

The WRX varies depending on the transmission type. The automatic has a
computer-controlled "variable torque distribution" mechanism which can be
turned into a pure FWD with a little fuse in the fusebox under the hood.

The front wheels of the 4-speed automatic have an open differential (unlike
the STi) as do the manual transmission's wheels. Wide open. One front wheel
can spin freely of the other.

The default split for the automatic is 45/55 rear bias. The default split
for the manual is a straight 50/50, period. No variation.

The automatic transmission can vary it up to a maximum of 50/50 from its
original 45/55.

For the STi, it's all different. The front wheels have a limited-slip
differential apparently deliberately added to introduce understeer in an
effort to "cup" the road better, according to a Japanese interview with a
Subaru exec I saw.

The front differential type for the Subaru STi is a "Suretrac viscous
limited slip", the center is a clutch-type limited slip, and the rear is a
mechanical limited slip.

The centre differential can be driver-controlled: there isn't much detail
about this mechanism in the user's manual for some reason, but in essence
you can directly lock the front and rear wheels together for snowy or icy
conditions in a 50/50 torque split (it works pretty well too,) or you can
open up the differential as wide as a 65/35, which can allow a bit of wheel
spin on the rear wheels during, for example, a hard launch.

I personally notice a definite improvement in forward acceleration when I
fully open the DCCD, although the driving characteristics feel a bit
strange by comparison with "Auto".

In locked mode, you can tell there's a difference when you drive very slowly
in the tightest arc you can: the inside wheels will slip and shimmy. In
auto or unlocked, there is none.