Forester Different Sized Tires

[Mel]

Where is the fuse on a 2003 Forester that converts the car from AWD to FWD.
I am getting 4 new tires, and I want to make sure I know how to turn off the
AWD if I get a flat.

What do you do if one of tires goes bad and needs to be replaced, say after
they have 30,000 miles on them? I am concerned about breaking the AWD
system.

How do I know if the difference in the size (due to wear) of the tires is a
problem or not?


Thanks a lot.

Mel

 

[Guest]

Where is the fuse on a 2003 Forester that converts the car from AWD to FWD.
I am getting 4 new tires, and I want to make sure I know how to turn off the
AWD if I get a flat.

What do you do if one of tires goes bad and needs to be replaced, say after
they have 30,000 miles on them? I am concerned about breaking the AWD
system.

How do I know if the difference in the size (due to wear) of the tires is a
problem or not?

Thanks a lot.

Mel

The fuse location is usually under the hood, there should be a covered
fuse panel. This is only on automatic transmission cars, however.
Manual trans and you have to stay below 50mph or something like that.

Subaru says the tires have to be within 1/4 inch in circumference to
prevent damage to the AWD system.

There are 3 options when you have tires with some wear and you need to
replace one:
1) replace all of 'em
2) Buy a new tire and have it 'shaved' to match (usually must be done
before any driving is done on the tire)
3) Find a used tire the right size. Same brand and model, or odd
handling may occur.


Dave

 

[Guest]

The fuse location is usually under the hood, there should be a covered
fuse panel. This is only on automatic transmission cars, however.
Manual trans and you have to stay below 50mph or something like that.

Subaru says the tires have to be within 1/4 inch in circumference to
prevent damage to the AWD system.

There are 3 options when you have tires with some wear and you need to
replace one:
1) replace all of 'em
2) Buy a new tire and have it 'shaved' to match (usually must be done
before any driving is done on the tire)
3) Find a used tire the right size. Same brand and model, or odd
handling may occur.

Dave

Oh, option 4, only an option if you don't have a limited-slip
differential:
get 2 new tires, put one in the front, and one in the back on the
opposite side.

Odd handling is a (remote, IMHO) possibility.


Dave

 

[Tony Hwang]

Where is the fuse on a 2003 Forester that converts the car from AWD to FWD.
I am getting 4 new tires, and I want to make sure I know how to turn off the
AWD if I get a flat.

What do you do if one of tires goes bad and needs to be replaced, say after
they have 30,000 miles on them? I am concerned about breaking the AWD
system.

How do I know if the difference in the size (due to wear) of the tires is a
problem or not?


Thanks a lot.

Mel

Hi,
No owner's manual?

 

[Rodney Lake]

I know where the fuse is that converts to FWD, but it seems to me it would
be better if Subaru had just put a toggle switch on the dash to do the job.
I seldom need 4WD and I am smart enough to know when I do need it. I would
prefer to drive most of the time in FWD and the switch would allow easy
change to FWD when it is needed.

Is there some technical reason why this is not possible?

 

[Yousuf Khan]

I know where the fuse is that converts to FWD, but it seems to me it would
be better if Subaru had just put a toggle switch on the dash to do the job.
I seldom need 4WD and I am smart enough to know when I do need it. I would
prefer to drive most of the time in FWD and the switch would allow easy
change to FWD when it is needed.

Is there some technical reason why this is not possible?

Why did you buy a Subaru if you don't need the 4WD? Anyways, Subarus
usually have 3 or 4 different AWD systems that they use. One version
goes on low-end manual transmission versions, which is all
fluid-mechanical -- it can't ever be turned off.

Then there is one that goes on low-end automatic transmissions, which is
basically an on-off system. It acts in FWD mode most of the time, and
then switches to AWD when it detects some slippage in the wheels. This
is likely the system that you have, and this is what the fuse is for, it
prevents the wheels from ever going into AWD mode. For the most part,
when you are not driving in anything slippery then you are already
driving only in FWD mode. So why would you want to disable the fuse on a
full-time basis? That fuse is there for specific situations like when
you're being towed. Otherwise, the car is already deciding to keep you
in FWD mode anyways.

Then there are two more sophisticated high-end AWD systems. One they use
on the high-performance STI car. The other one they use in the high end
cars with VDC (vehicle dynamics control). I don't think they apply to you.

Yousuf Khan

 

[Dano58]

I know where the fuse is that converts to FWD, but it seems to me it would
be better if Subaru had just put a toggle switch on the dash to do the job.
I seldom need 4WD and I am smart enough to know when I do need it.  I would
prefer to drive most of the time in FWD and the switch would allow easy
change to FWD when it is needed.

Is there some technical reason why this is not possible?

No, a marketing reason. Subaru trumpets the benefits of full-time AWD
(versus the 'on demand' systems that many other manufacturers use). So
why would they then allow you to switch between 2WD and AWD?

Dan D
'99 Impreza 2.5 RS (son's)
Central NJ USA

 

[Carl 1 Lucky Texan]

I know where the fuse is that converts to FWD, but it seems to me it would
be better if Subaru had just put a toggle switch on the dash to do the job.
I seldom need 4WD and I am smart enough to know when I do need it. I would
prefer to drive most of the time in FWD and the switch would allow easy
change to FWD when it is needed.

Is there some technical reason why this is not possible?

There was a long discussion over at www.ultimatesubaru.org on methods
to create just such a switch. You might try a search there.

Carl

 

[Valued Corporate #120,345 Employee (B A R R Y)]

No, a marketing reason. Subaru trumpets the benefits of full-time AWD
(versus the 'on demand' systems that many other manufacturers use). So
why would they then allow you to switch between 2WD and AWD?

What other cars (not trucks!) can turn off AWD?

 

[Guest]

I know where the fuse is that converts to FWD, but it seems to me it would
be better if Subaru had just put a toggle switch on the dash to do the job.
I seldom need 4WD and I am smart enough to know when I do need it. I would
prefer to drive most of the time in FWD and the switch would allow easy
change to FWD when it is needed.

Is there some technical reason why this is not possible?

A switch is perfectly possible, but the MPG gain will be quite small
(if at all) since all the drivetrain will be spinning anyway.

Also, the solenoid that dumps the pump pressure (allowing the front/
rear clutchpack to spin free) is not made for a 100% duty cycle. It
will likely eventually fail if always energized.


Dave

 

[Rodney Lake]

A switch is perfectly possible, but the MPG gain will be quite small
(if at all) since all the drivetrain will be spinning anyway.

Also, the solenoid that dumps the pump pressure (allowing the front/
rear clutchpack to spin free) is not made for a 100% duty cycle. It
will likely eventually fail if always energized.


Dave

The possible solenoid failure makes sense and rules out a switch.

I bought this forester in 07 because I had owned several subarus prior to
1990 before they had full time AWD. These were sturdy cars with good gas
mileage. the salesman who went with me for a test drive seemed like a nice
sort and I made a lowball cash offer to keep his boss happy. They accepted
it so now I have one. It seems like a nice car but the problems associated
with different tire sizes and the timing belt mean that I will probably
trade for a toyota in a couple years. I don't see any advantage to AWD
since most of my driving is on dry pavement.

 

[mylesv]

The fuse location is usually under the hood, there should be a covered
fuse panel. This is only on automatic transmission cars, however.
Manual trans and you have to stay below 50mph or something like that.

Subaru says the tires have to be within 1/4 inch in circumference to
prevent damage to the AWD system.

There are 3 options when you have tires with some wear and you need to
replace one:
1) replace all of 'em
2) Buy a new tire and have it 'shaved' to match (usually must be done
before any driving is done on the tire)
3) Find a used tire the right size. Same brand and model, or odd
handling may occur.

Dave

Could someone tell me where this "1/4" circumference" rule comes
from? I see no such thing in my US-market 2002 Legacy owner's
manual. I'll check the factory service manuals when I get home.

 

[Guest]

Why did you buy a Subaru if you don't need the 4WD? Anyways, Subarus
usually have 3 or 4 different AWD systems that they use. One version
goes on low-end manual transmission versions, which is all
fluid-mechanical -- it can't ever be turned off.

Then there is one that goes on low-end automatic transmissions, which is
basically an on-off system. It acts in FWD mode most of the time, and
then switches to AWD when it detects some slippage in the wheels. This
is likely the system that you have, and this is what the fuse is for, it
prevents the wheels from ever going into AWD mode. For the most part,
when you are not driving in anything slippery then you are already
driving only in FWD mode. So why would you want to disable the fuse on a
full-time basis? That fuse is there for specific situations like when
you're being towed. Otherwise, the car is already deciding to keep you
in FWD mode anyways.

Then there are two more sophisticated high-end AWD systems. One they use
on the high-performance STI car. The other one they use in the high end
cars with VDC (vehicle dynamics control). I don't think they apply to you.

Yousuf Khan

The low-end automatic system is a bit better than you describe, in the
later generation subarus (like my '03)

The duty-c solenoid (100% energized=rear wheels disconnected, 0%
energized, rear locked to front) is strobed with a varying pulse-width
signal to achieve different degrees of coupling between the front and
rear wheels.

Typically the front-rear ratio is 90/10, when slip is detected, or
when full-throttle is applied, or when the shifter is in 1,2, or R the
duty C soenoid is minimally strobed and egffectively a 50/50 front/
rear torque split is achieved.

(note- 50/50 meaning rear driveshaft 'locked' to the 'front'
driveshaft, the notional front driveshaft never actually leaving the
trans case)


Dave

 

[Valued Corporate #120,345 Employee (B A R R Y)]

Could someone tell me where this "1/4" circumference" rule comes
from? I see no such thing in my US-market 2002 Legacy owner's
manual. I'll check the factory service manuals when I get home.

My '01 OBW did in fact have a specific measurement listed in the
manual. I no longer have the car, so I can't point you to a section.

 

[Dano58]

What other cars (not trucks!) can turn off AWD?

Plenty. In fact, MOST cars that advertise 'AWD' are really part-time
systems, where they are FWD (i.e., Audi TT*) or RWD (i.e., Infiniti
G37) until the system detects slippage, then routes power to the other
set of wheels. This results in a momentary delay in getting the 'AWD'
engaged, which could prove to be the difference between control and
not.

As far as I know, Subaru is really the only company that equips all of
their US cars with full-time AWD as a standard feature.

*Audi calls their AWD 'quattro' on all of their cars, but actually
uses 2 different systems - one for cars with transverse engines like
the TT and A3, another - with REAL fulltime AWD - for the
longitudinally-equipped cars like the A4, A5, A6 and A8.

Dan D
'99 Impreza 2.5 RS (son's)
Central NJ USA