AWD and Donuts
BRH
unusual to get a full sized spare with a car nowadays, and that I was
happy to get one with the Forester. The dealer then explained to me
that the reason for the full-sized spare was the AWD in the Forester.
He explained that using a donut or a different sized tire as a spare
would likely damage the AWD system.
Well, my father bought a 1995 Legacy sedan (used) which, according to
him, has AWD. In fact there's a sticker on the back windshield that
says "AWD" on it. However, his car is equipped only with a donut for a
spare tire. In fact the wheel well for the spare isn't even big enough
to hold a full-sized tire. This makes me doubt whether his car really
has AWD.
Can anyone shed any light on this? Are 1995 Legacy sedans equipped with
AWD? If they are, why the donut for a spare tire? Is there a quick and
dirty way to determine whether its equipped with AWD?
Thanks.
Jail Worm
"BRH @attbi.com>" <"bertrh<no-spam> wrote in message
news:3DD11257...@attbi.com...
I have a 2001 Outback, it came with a "donut" too. It is definately AWD.
Your dealer was probably paraphrasing the manual, which does state more or
less "do not use donut beyond 30 miles or over 45 mph".
So it is probably not a case of outright damage due to driving 10 feet, more
like "dont drive too fast or too far or you may cause excessive wear or heat
on the transmission."
I'd just tell him to get damaged tires fixed right away, and dont drive
around on it too long, but otherwise dont worry about it.
Koen
My Forester (1998) is, like many cars in Holland, equipped with a
gas-installation.
The tank fits exactly in the sparetire space.
Instead of a full-sized spare i got a small spare. (Which is at home in the
garage most of the times).
All the Forester's with a gas-installation come with a smal spare.
This tire is only suitable for limited speed and distance, it doesnt
influence the awd.
Koen.
"BRH @attbi.com>" <"bertrh<no-spam> schreef in bericht
news:3DD11257...@attbi.com...
Foxbat
dealer tells you is true. That why maunals list limitations on how
fast and how far you can go when you're on donuts.
However even with the full-size spare, I can see there is problems
because of the wear on you regular tires compared to your never used
spares unless you rotate your spare tire with your regulars to make it
wear evenly. In the end, it might not worth it to have the full-size
spare (additional weight and price).
BRH <"bertrh<no-spam>"@attbi.com> wrote in message news:<3DD11257...@attbi.com>...
Brian Wasson
course) has AWD. It does have room for a full-size spare, but the cost
to get a 16" rim and tire is pretty steep.
BRH <"bertrh<no-spam>"@attbi.com> wrote in message news:<3DD11257...@attbi.com>...
Aaron M
Both had donut spares. When driving with the spare, on an automatic, just
make sure to put a fuse in the engine compartment fuse box to engage FWD
mode as to not damage the AWD system when driving with the spare on.
It should be covered in the owner's manual.
Aaron
"BRH @attbi.com>" <"bertrh<no-spam> wrote in message
news:3DD11257...@attbi.com...
Hallraker
I don't know about current Subarus, but my 1995 Legacy Outback is equipped
with an odd donut that even my friend who works at Discount Tire remarked
was rather odd looking. A true full size spare can be rotated with the rest
of the tires. Sometimes this "spare" even has an aluminum or chrome wheel
attached to it, such as often seen on the back of a Jeep. A donut, on the
other hand, is a tiny wheel and tiny tire that are only designed to limp
your car to a tire repair place and nothing more. This small size results
in a difference between wheel speeds, which on an AWD vehicle can cause
damage or loss of control.
The special donut that came with my Subaru is actually a 16" donut. I've
never taken it out to compare, but by looking I would say that although it
is much narrower than the regular wheel and tire, it appears to be the exact
same diameter. Therefore, although the Legacy's spare is *not* a full size,
it is not really a true "compact spare" either, since in terms of diameter
it appears to be the same size. I guess if I were to try and name it, I
would refer to it as a "full diameter compact spare."
-Matt
Demon
"BRH @attbi.com>" <"bertrh<no-spam> wrote in message
news:3DD11257...@attbi.com...
Drifter
Your "donut" spare is full diameter. A smaller rolling diameter will cause
a difference in rotational speed between the left and right sides of the car
thus damaging the differential connecting those two drive wheels.
Subarus have THREE differentials... a center that controls front/rear bias,
a front diff that is OPEN (non-limited slip) that distributes torque to the
front wheels, and a rear diff that can be open or LSD depending on the
model. The Foresters and Outbacks typically have a rear LSD.
Automatic Subes can be converted to front wheel drive because their "center
diff" is actually an electronically controlled clutch pack that is integral
to the automatic transmission. You can disengage the center "diff" by
pulling a fuse.
You should NEVER use a smaller diameter spare tire than what you are
currently using on the other wheels, and you should NEVER tow a Subaru with
any of the wheels off the ground. They MUST be towed on a flatbed. Even
1-2 miles with uneven rotational distribution of any kind will DESTROY your
differentials leading to thousands of dollars in repair costs. It is even
ill-advised to use different types of tires on the front/rear or to use
tires with different levels of wear. Even 2% difference front/rear when
averaged out over thousands of miles causes binding in the center diff and
can destroy the differential. AWD vehicles should use identical tires on
all four corners of the car and the tires should be rotated REGULARLY to
protect the differentials.
Thanks!
-J. Porter
1994 Subaru Alcyone SVX LSi AWD
1991 Subaru Alcyone XT6 5MT AWD
DS
It's a wagon. SUVs are truck based.
DS
"Demon" <uda...@singapore.com> wrote in message
news:3dd2...@news.starhub.net.sg...
Gml...@scvnet.com
"Drifter" <jport...@altavista.com> wrote in message
news:ut4tvm...@corp.supernews.com...
> Wow. All kinds of weird thinking on this newsgroup.
That's for sure, even yours.
> You should NEVER use a smaller diameter spare tire than what you are
> currently using on the other wheels,
So far so good, unless the vehicle was designed to do just that, as several
Subarus have.
> and you should NEVER tow a Subaru with
> any of the wheels off the ground. They MUST be towed on a flatbed.
Good idea.
> Even
> 1-2 miles with uneven rotational distribution of any kind will DESTROY
your
> differentials leading to thousands of dollars in repair costs. It is even
> ill-advised to use different types of tires on the front/rear or to use
> tires with different levels of wear.
Here is where the advice turns from good to alarmist.
> Even 2% difference front/rear when
> averaged out over thousands of miles causes binding in the center diff and
> can destroy the differential.
Look up the definition of "differential". The purpose of the differential
is to allow the wheels to turn at different (differential, get it?) speeds.
A 2% difference won't make any difference and even with new tires you are
likely to get more than a 2% difference with variations in loading,
pressure, etc. It takes a considerably larger difference to bring the
limited slip or center lock into play.
> AWD vehicles should use identical tires on
> all four corners of the car and the tires should be rotated REGULARLY to
> protect the differentials.
Yes, and while you're at it, you should only rotate them in the dark of the
new moon after the ritual sacrifice of several roosters. Blood-letting for
automatics only.
Or, you could look at the owner's manual for the straight information.
The Subaru engineers didn't make their system so fragile that it would be
destroyed the first time the car was run with a low tire. If they did,
Subarus would have a worse reputation for quality than Yugo.
B a r r y B u r k e J r .
The bottom line is the transmission.
Is the Forester a 5 speed? Was the Legacy an automatic?
Subaru automatics use _electric_ clutches to engage the rear wheels.
They run in FWD mode most of the time. This can be easily disabled by
inserting a fuse. Manual transmission vehicles use a mechanical AWD
system that cannot be disabled.
FWIW, my '01 Outback with a 5 speed manual tranny came with what looks
like a donut. Upon close investigation, it's actually a narrow,
full-height tire.
Barry
John
95 LS is the same as the full 15" alloy with a stock 195/60 mounted. This
should have no ill effect on AWD performance (other than its very narrow
width) or damage caused to the AWD system.
The mileage and speed ratings for the donut are exactly that, for the donut.
Just as all full-size tires have speed ratings, so does the donut. It is
not built to withstand the heat of high-speed/long distance driving.
--
John
"Hallraker" <hallr...@nospam.hotmail.com> wrote in message
news:Y8lA9.15927$V16.20039@rwcrnsc54...
Decimal Cat
statement may be correct for the newer Subarus, my 91 Loyale (4WD on demand,
FWD otherwise) was towed about 20 miles a few months ago with just the front
wheels off the ground, back wheels rolling, and there was no drive train
damage at all.
--Decimal Cat
"Drifter" <jport...@altavista.com> wrote in message
news:ut4tvm...@corp.supernews.com...
> You should NEVER use a smaller diameter spare tire than what you are
Foxbat
"Tom Hickey" <n...@chance.com> wrote in message
news:vhf6tugkctk8p2f4u...@4ax.com...
> On Wed, 13 Nov 2002 23:55:12 GMT, "B a r r y B u r k e J r ."
<*barry_b*@snet.net> wrote:
> "FWD" ??
>
> Also, you make it sound like auto AWD is part-time and performed entirely
by silicone and wires, but
> it is not: "The system uses complex planetary gear type centre
differentials that distribute the
> basic torque at a ratio of 35 for the front wheels and 65 for the rear."
>
The system you described here is called VTD AWD which is only available to
WRX and Outback VDC models. All other Auto Subarus use MPT system that only
contains a electronically controlled Multi-Plate Transfer Clutch to send
power to the rear axle.
B a r r y B u r k e J r .
>
> On Wed, 13 Nov 2002 23:55:12 GMT, "B a r r y B u r k e J r ." <*barry_b*@snet.net> wrote:
>
> >
> >Is the Forester a 5 speed? Was the Legacy an automatic?
> >
> >Subaru automatics use _electric_ clutches to engage the rear wheels.
> >They run in FWD mode most of the time. This can be easily disabled by
> >inserting a fuse. Manual transmission vehicles use a mechanical AWD
> >system that cannot be disabled.
>
>
> Also, you make it sound like auto AWD is part-time and performed entirely by silicone and wires, but
> it is not: "The system uses complex planetary gear type centre differentials that distribute the
> basic torque at a ratio of 35 for the front wheels and 65 for the rear."
>
>
> Some light reading follows:
>
> http://www.subaru-global.com/about/awd/2321.html
>
> "This system for MANUAL TRANSMISSION vehicles combines a centre differential with bevel gears and a
> viscous coupling type limited slip differential (LSD)."
>
> "Normally, the centre differential distributes the torque at a ratio of 50:50 to the front and rear
> wheels for extremely stable driving and maximum traction."
>
> "Where the balance of traction is lost when front or rear wheels slip, viscous LSD automatically
> redistributes torque to maximise grip, so full traction and driveability are always available."
>
> http://www.subaru-global.com/about/awd/2322.html
>
> "Active Torque Split AWD is a system that makes the most of stable driving performance of AUTOMATIC
> TRANSMISSION vehicles under any road conditions."
>
> "Vehicle conditions such as variations in front and rear tyre grip, vehicle speed, and so on, are
> constantly monitored by sensors. Based on torque distribution readouts and directly coupled to front
> and rear tyres, it dramatically stabilises traction performance."
>
> "Electronic Control MP-T (MultiPlate Transfer) is a device that increases AWD stability and driving
> pleasure by controlling the distribution of torque to the front and rear wheels in real time,
> responding directly to driving conditions. "
>
> http://www.subaru-global.com/about/awd/2323.html
>
> "V-T-D AWD is an AWD system for automatic transmission vehicles that provides positive, sporty
> driving by making improvements in turning-in while maintaining the basic driving safety performance
> of Subaru AWD."
>
> "The system uses complex planetary gear type centre differentials that distribute the basic torque
> wheels reduces the tendency to understeer when accelerating while cornering to provide smoother,
> more confident handling."
>
> "Torque distribution is also optimally controlled to suit road conditions. This system provides both
> sporty driving and stability under any road conditions by automatically equalizing the front and
> rear wheel torque distribution to a maximum ratio of 50:50."
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> When you get it, you get it.
> The Beauty of Subaru All-Wheel Drive.
B a r r y B u r k e J r .
>
> On Wed, 13 Nov 2002 23:55:12 GMT, "B a r r y B u r k e J r ." <*barry_b*@snet.net> wrote:
>
> >
> >Is the Forester a 5 speed? Was the Legacy an automatic?
> >
> >Subaru automatics use _electric_ clutches to engage the rear wheels.
> >They run in FWD mode most of the time. This can be easily disabled by
> >inserting a fuse. Manual transmission vehicles use a mechanical AWD
> >system that cannot be disabled.
>
>
> Also, you make it sound like auto AWD is part-time and performed entirely by silicone and wires, but
> it is not: "The system uses complex planetary gear type centre differentials that distribute the
> basic torque at a ratio of 35 for the front wheels and 65 for the rear."
Only on the VDC. The everyday automatic is more like 90-10.
Note that this link <http://www.subaru-global.com/about/awd/2322.html>
that you posted never mentions the split. As I understand it Honda's
"Realtime 4WD" works the same way.
This is the primary reason that Subaru autos get the same mileage as the
manual tranny equipped cars.
> http://www.subaru-global.com/about/awd/2322.html
>
> "Vehicle conditions such as variations in front and rear tyre grip, vehicle speed, and so on, are
> constantly monitored by sensors. Based on torque distribution readouts and directly coupled to front
> and rear tyres, it dramatically stabilises traction performance."
"Sensors" sound like silicon and wires to me! <G>
> "Electronic Control MP-T (MultiPlate Transfer) is a device that increases AWD stability and driving
> pleasure by controlling the distribution of torque to the front and rear wheels in real time,
> responding directly to driving conditions. "
Still no mention of the split....
Barry
B a r r y B u r k e J r .
>
> Also, you make it sound like auto AWD is part-time and performed entirely by silicone and wires
Light reading for you, Tom:
From:
<http://autos.msn.com/vip/job.aspx?modelid=9986&src=vip&MSID=4CE9081DA10847699F45C04723CA1533>
Comparing the VDC: "This compares with the other Outbacks with
automatic transmission that come with a hydraulically controlled clutch
and where the torque split is 90 percent front and 10 percent rear in
normal driving."
And here's more to keep you going all night:
<http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=subaru+torque+90+split&btnG=Google+Search>
Have fun,
Barry
Tony Hwang
Gas-installation = Propane gas installation?
Gas is commonly refered as gasoline over this side of the pond.
Tony
Tony Hwang
Atta boy. Here is one who reads manual B4 shooting off his mouth
exposing his ignorance. If everyone spends some time reading manual,
all the dumb questions on this NG will be reduced a lot.
Also AWD should be disabled with the fuse when towed on ground.
Tony
Tony Hwang
SUV? Huh?
Maybe Wannabe SUV.
Tony
Dave Carlson
disable the AWD by
putting a fuse in the fuse box (located in the engine area.) I have tried
it and the car drives like
a front - wheel drive . Perhaps the 95 Legacy had the same feature.
Dave
"BRH @attbi.com>" <"bertrh<no-spam> wrote in message
news:3DD11257...@attbi.com...
Yousuf Khan
news:3DD467C6...@snet.net...
> Note that this link <http://www.subaru-global.com/about/awd/2322.html>
> that you posted never mentions the split. As I understand it Honda's
> "Realtime 4WD" works the same way.
>
> This is the primary reason that Subaru autos get the same mileage as the
> manual tranny equipped cars.
Are you sure it isn't because the manual cars have lower gear ratios than
their automatic bretheren? At exactly 100kph, my tach is reading almost
exactly 3000rpm, in 5th. I think at the same speed an auto would only be
reading 2500rpm or less.
I've thought for a while now that manual Subies should be equiped with a 6th
or 7th gear to get properly fuel economy out of it.
Yousuf Khan
B a r r y B u r k e J r .
>
> > This is the primary reason that Subaru autos get the same mileage as the
> > manual tranny equipped cars.
>
> Are you sure it isn't because the manual cars have lower gear ratios than
> their automatic bretheren? At exactly 100kph, my tach is reading almost
> exactly 3000rpm, in 5th. I think at the same speed an auto would only be
> reading 2500rpm or less.
>
> I've thought for a while now that manual Subies should be equiped with a 6th
> or 7th gear to get properly fuel economy out of it.
>
> Yousuf Khan
Could be, but many cars have different ratios in different
transmissions.
I was told the the manual Subarus, mine included, pushed more driveline
drag due to the AWD being 50-50, than the autos. On a dry road the
automatics are pretty much front wheel drive.
Barry
Yousuf Khan
> I was told the the manual Subarus, mine included, pushed more driveline
> drag due to the AWD being 50-50, than the autos. On a dry road the
> automatics are pretty much front wheel drive.
I think the whole 4WD having more drag than 2WD thing is a gross
oversimplification, bordering on an urban legend now. I think the rumours of
drag are from looking at part-time 4WD systems which don't have central
differentials. Without the central diffs, the front and rear axles which
usually follow different radii during turns, are forced to follow nearly
identical turning radii -- unnaturally. You can see that there is bound to
be a lot of friction in such a system. You definitely have to run that in
2WD mode most of the time.
Full-time 4WD systems on the other hand of central diffs and are meant to be
used all of the time without undue drag. I guess people just don't make a
distinction between part-time and full-time.
Yousuf Khan
T Berk
> Koen wrote:
> > Something from the Netherlands,
> >
> > My Forester (1998) is, like many cars in Holland, equipped with a
> > gas-installation.
> > The tank fits exactly in the sparetire space.
> >
> > Instead of a full-sized spare i got a small spare. (Which is at home in the
> > garage most of the times).
> > All the Forester's with a gas-installation come with a smal spare.
> > This tire is only suitable for limited speed and distance, it doesnt
> > influence the awd.
> >
> > Koen.
> >
>
> Hi,
> Gas-installation = Propane gas installation?
> Gas is commonly refered as gasoline over this side of the pond.
> Tony
>
Tony,
sounds like he means a supplemental tank that fits in the spare tire
well, but I could be wrong.
TBerk
B a r r y B u r k e J r .
I own a 4WD Jeep Wrangler and an Outback, so I know what you mean about
turning a 4WD vehicle on dry pavement vs. AWD.
However, that wasn't what I meant at all. Let's assume we've lifted the
whees off the ground. Wouldn't a manual transmission Subaru experience
more friction drag simply from the extra moving parts the engine is
required to move?
Barry
Yousuf Khan
> I own a 4WD Jeep Wrangler and an Outback, so I know what you mean about
> turning a 4WD vehicle on dry pavement vs. AWD.
>
> However, that wasn't what I meant at all. Let's assume we've lifted the
> whees off the ground. Wouldn't a manual transmission Subaru experience
> more friction drag simply from the extra moving parts the engine is
> required to move?
Yes, a little, but I don't think that's the major cause of lower gas
mileage -- let's face it these drivetrains are well-lubricated otherwise
they wouldn't be properly designed. Tests have shown that with cars with
full-time 4WD vs. the same car with 2WD, the 2WD version has approx. 2mpg
better fuel economy. That pretty much corresponds to the additional weight
of the 4WD version of the car. The extra drivetrain components add weight to
the overall system.
A draggy part-time 4WD system would have the added weight, as well as the
additional friction due to the lack of central diff to contend with. The
full-time 4WD would only worry about the additional weight. You can expect
to see some major hits to fuel economy in a part-time 4WD system when 4WD
mode is engaged, but not so with full-time 4WD.
Yousuf Khan