Forester L vs S - AWD tech question.
Joseph
I have been looking at buying a used Forester - probably a 2001. One of
the differences between the L and S models is the fact that the S has a
Limited-Slip differential in the rear. This has me confused because thier
AWD is supposed to "transfer power from the wheels that slip to the wheels
that grip" . If the electronics controlling the AWD can move the power from
side to side as well as front to rear then I don't see any value in the
limited-slip differential. After reading everything I could find, I am now
believing that the AWD system just controls the center diff and moves power
fore and aft. It looks like the front and rear differentials are "open" -
at least on the L model. If this is true, then I can see where the
limited-slip differentail would be useful because it would take whatever
power was set to the rear and move it to the left or right depending on the
traction conditions.
So my bottom line question is : Does anybody know for sure if the AWD on
the Forester L (auto trans) controls power distribution to each wheel or is
it just front to back.??
Thanks very much.
Joseph
**Please reply to the group not my email.**
TransFixed
> Hi
>
> I have been looking at buying a used Forester - probably a 2001. One of
> the differences between the L and S models is the fact that the S has a
> Limited-Slip differential in the rear. This has me confused because thier
> AWD is supposed to "transfer power from the wheels that slip to the wheels
> that grip" . If the electronics controlling the AWD can move the power from
> side to side as well as front to rear then I don't see any value in the
> limited-slip differential. After reading everything I could find, I am now
> believing that the AWD system just controls the center diff and moves power
> fore and aft.
You read correctly.
> It looks like the front and rear differentials are "open" -
> at least on the L model. If this is true, then I can see where the
> limited-slip differentail would be useful because it would take whatever
> power was set to the rear and move it to the left or right depending on the
> traction conditions.
In addition, now the rear can *take* more torque. Also, one rear wheel
with traction is all you need to get going. Two slipping rears and one
slipping front tire will leave you stuck, though (a fairly rare case,
admittedly).
> So my bottom line question is : Does anybody know for sure if the AWD on
> the Forester L (auto trans) controls power distribution to each wheel or is
> it just front to back.??
In my opinion, for a car like the Forester (excluding perhaps the XT)
and ABS-based traction control that brakes slipping wheels would be a
cheaper, lighter, and more practical solution than a single LSD. But
you are right, Subaru does not offer that.
For optimum acceleration and high speed AWD functionality, LSDs are
better (albeit still heavier) than a brake-based system.
> Thanks very much.
You are welcome. You may find some of the info under AWD on the Subaru
web site helpful (although most of it is marketing language).
- D.
Pat F
not the auto
"Joseph" <no...@nowhere.com> wrote in message
news:3ed1309e$1...@news.athenanews.com...
TransFixed
> Just for your info,,, the Limited slip is only on the manual transmission...
> not the aut
He was talking about the rear LSD, which is on both, the auto and the
manual.
- D.
PeterV
2001 Forester.
I don't know if it varies between countries...
"TransFixed" <ey...@2003forester.jp> wrote in message
news:3ED1BF5C...@2003forester.jp...
TransFixed
> Very strange, to the best of my knowledge the rear LSD is only in the Auto
> 2001 Forester.
> I don't know if it varies between countries...
I may be wrong, but I believe in the US for the 2000-2002 models the
rear LSD came with the All Weather Package, regardless of the
transmission, and may have been an idependent option on all models.
Someone with a manual 2000-2002 US Forester may want to chime in.
- D.
Edward Hayes
TransFixed
> All Forester "S" models have the limited slip differential. Ed
Thanks, Ed, although I am still confused whether the LSD at one time was
available as an option, either separately or in a package (cold weather
package) on *all* models.
At any rate, the main task was to clarify that at least in the US,
availability of the rear LSD was never related to what transmission the
Forester had. There is no good reason to make such a distinction, anyway.
- D.
D Heath
news:cUJAa.175733$ja4.8...@bgtnsc05-news.ops.worldnet.att.net...
> All Forester "S" models have the limited slip differential. Ed
Not before 2000, they didn't. Our two 99 S-models have NO limited slip.
(Bummer.) It might have been a separate option, but I'm not sure it was even
available yet. (Bad memory.)
--
Off to ride the mountains, Dale Heath
To reply, poke out my eye.
PeterV
'Limited' model (being one-up from the basic model, which had no name).
"Edward Hayes" <hay...@worldnet.att.net> wrote in message
news:cUJAa.175733$ja4.8...@bgtnsc05-news.ops.worldnet.att.net...
PeterV
difference between Auto and Manual - The manual has centre diff while the
auto has an electronic clutch-plate and NO centre diff)
That fact alone would lead you to believe that there is likely to be other
differences between the two transmissions.
"TransFixed" <ey...@2003forester.jp> wrote in message
news:3ED45EAB...@2003forester.jp...
TransFixed
If you did a quick search, you'd realize that I have made a number of
posts on the difference between the AWD systems available for the two
transmission types. So yes, I am very familiar with that. However, a
rear LSD has nothing to do with the transmission. As long as you have a
RWD or AWD car, you can slap on a rear LSD. The goal of the rear LSD is
to improve traction between the rear sides, a function at first
unrelated to the transmission.
However, the type of AWD (and thus, indirectly, with Subarus the type of
transmission) does come in with non-mechanical implementations of
left-right torque control, or when adding a front LSD.
A traction control mechanism depends on the AWD type, since it requires
a more sophisticated control system if you have a viscous center diff
vs. an open diff, and yet another system if there is no center diff.
So, Subaru would have to develop two new and different systems for the
same car. Looks like they think it is too expensive to do such
development, given that they only sell traction control in their premium
AT models (open center diff with clutch pack).
A front LSD can be a problem on some types of AWD that require slippage
to occur to transmit power to the back. The problem is stability, since
you basically will have lost most front grip and steering before your
car practically and almost instantaneously turns into a RWD car... I
wouldn't want to drive such a vehicle.
- D.
morden
> A front LSD can be a problem on some types of AWD that require slippage
> to occur to transmit power to the back. The problem is stability, since
> you basically will have lost most front grip and steering before your
> car practically and almost instantaneously turns into a RWD car... I
> wouldn't want to drive such a vehicle.
>
LSD option. The situation you're describing does not apply to STi...
does it? I mean, since the rear wheels are driven under normal
conditions. It must be very interested to see how STi behaves on a road
covered with a lot of black ice patches. Any predictions?
TransFixed
> TransFixed wrote:
>
>> A front LSD can be a problem on some types of AWD that require
>> slippage to occur to transmit power to the back. The problem is
>> stability, since you basically will have lost most front grip and
>> steering before your car practically and almost instantaneously turns
>> into a RWD car... I wouldn't want to drive such a vehicle.
>>
> And I thought there's nothing worse than the late Maxima with the front
> LSD option.
I think it comes down to performance vs. safety. A front LSD on a FWD
car helps avoid some torque steer and will give you better acceleration
both in a straight line and in a curve. But you lose quite a bit margin
of safety, since you can accelerate up to the point where you have no
traction left (that is, no traction for steering, either) and massive
understeer. I could be wrong but I have a hunch this is why so many
street racers end up in the ditch.
> The situation you're describing does not apply to STi...
> does it? I mean, since the rear wheels are driven under normal
> conditions.
Yeah, as I said, I am particularly leary of front LSDs on AWD cars that
rely on front slippeage to transfer power to the back. That does not
apply to the STi nor the WRX nor the manual Forester. It does apply to
the auto Forester, which does not have a center diff, or e.g., to the CR-V.
However, I believe any AWD car with just a front LSD is somewhat tricky,
since you remove traction available for steering just when you need it
most. In the STi you have the rear LSD in addition, so on average, you
will have less power up front and take less traction away from steering.
And hopefully, you can sense when your rear gets loose and ease off
the gas a little, if necessary.
> It must be very interested to see how STi behaves on a road
> covered with a lot of black ice patches. Any predictions?
I remember the thread where some people argued the STi is not a
winter/snow car, but I did not understand the arguments. I think apart
from a little less clearance (and given the same tires), it should do as
well as the WRX, if you are a bit carful with the gas pedal.
With a lot of black ice patches, having power at all four corners helps
to avoid problems, and an electronic stability control program can
correct minor problems. But there is only so much you can do, when
chances are that you have reduced traction on all four wheels. In the
end, you would need *better* than average traction to be able to do all
of your breaking and steering on a single wheel...
- D.
morden
> morden wrote:
>
> Yeah, as I said, I am particularly leary of front LSDs on AWD cars that
> rely on front slippeage to transfer power to the back. That does not
> apply to the STi nor the WRX nor the manual Forester. It does apply to
> the auto Forester, which does not have a center diff, or e.g., to the CR-V.
But Forester does not have a front LSD, does it? I'm slow...
>
> However, I believe any AWD car with just a front LSD is somewhat tricky,
> since you remove traction available for steering just when you need it
> most. In the STi you have the rear LSD in addition, so on average, you
> will have less power up front and take less traction away from steering.
> And hopefully, you can sense when your rear gets loose and ease off
> the gas a little, if necessary.
Assuming that the front will follow soon? It seems to me that that
LSD is more of a hinderance in a rally car then because you'd be more
conservative and leery of finding the limits when you have front LSD.
>> It must be very interested to see how STi behaves on a road covered
>> with a lot of black ice patches. Any predictions?
>
>
> I remember the thread where some people argued the STi is not a
> winter/snow car, but I did not understand the arguments. I think apart
> from a little less clearance (and given the same tires), it should do as
> well as the WRX, if you are a bit carful with the gas pedal.
>
> With a lot of black ice patches, having power at all four corners helps
> to avoid problems, and an electronic stability control program can
> correct minor problems. But there is only so much you can do, when
> chances are that you have reduced traction on all four wheels. In the
> end, you would need *better* than average traction to be able to do all
> of your breaking and steering on a single wheel...
>
What if the rear wheels and one of the fronts lose traction on STi?
The poer goes to the front and you lose whatever traction you've had on
the remaining wheel...
TransFixed
> TransFixed wrote:
>
>> morden wrote:
>
>
>>
>> Yeah, as I said, I am particularly leary of front LSDs on AWD cars
>> that rely on front slippeage to transfer power to the back. That does
>> not apply to the STi nor the WRX nor the manual Forester. It does
>> apply to the auto Forester, which does not have a center diff, or
>> e.g., to the CR-V.
>
>
> But Forester does not have a front LSD, does it? I'm slow...
Sorry, I was talking about if you would add one yourself.
>
>>
>> However, I believe any AWD car with just a front LSD is somewhat
>> tricky, since you remove traction available for steering just when you
>> need it most. In the STi you have the rear LSD in addition, so on
>> average, you will have less power up front and take less traction away
>> from steering. And hopefully, you can sense when your rear gets
>> loose and ease off the gas a little, if necessary.
>
>
> Assuming that the front will follow soon? It seems to me that that
> LSD is more of a hinderance in a rally car then because you'd be more
> conservative and leery of finding the limits when you have front LSD.
>
I am not a rally driver, so I am not qualified to answer that. But my
guess is that an experienced driver has absolutely no problem
recognizing that limit. On the plus side, since the inside wheels
typically go first, you have almost twice as much acceleration traction
for a while (both outside wheels instead of just the back, where without
a front LSD the front has ceased to receive power due to the inside
wheel spinning).
...
> What if the rear wheels and one of the fronts lose traction on STi?
> The poer goes to the front and you lose whatever traction you've had on
> the remaining wheel...
In a FWD car you lose traction on the inside front wheel all the time,
so with a front LSD you are in a potentially dangerous position in any
curve that you accelerate around quickly. With AWD, if you lose
traction on three wheels, you are either driving intentionally
borderline or simply too fast, and hopefully know that. I contend not
only can you accelerate more and earlier in the AWD car, but you have a
wider margin once you feel slippage. Of course, if you ignore that and
continue to accelerate, you are back to gambling as in the FWD LSD
situation.
- D.
TransFixed
> I am not a rally driver, so I am not qualified to answer that. But my
> guess is that an experienced driver has absolutely no problem
> recognizing that limit.
OK, I may have to correct myself on this one. Say, an experienced
driver with a lot of practice on the STi.
See the STi comparison link I just posted as a new thread, for details.
- D.
PS It is a bit funny, though, that we just talked about that. The
relatively simple AWD set-ups without front (or rear) LSD in the Evo and
in the R32 (*) seem to produce a much more predictable borderline
behavior. Looks like it really takes a lot of learning to make use of
the added acceleration traction of the front LSD without going into a spin.
(*) Of course, the R32 has a sophisticated ESP, which can help tremendously.