FWD mode

[rcyoungs]

I have a 2004 forester automatic. I understand that there is a clutch
mechanism which regulates power between the front and rear wheels.

I am told that under typical driving conditions 90% of the power goes
to the front wheels while the remaining 10% goes to the rear wheels.
This would be essentially a front wheel drive car under usual
conditions with 10% simply rotating the rear wheels.

I would expect that when driving on a straight level highway, as
we have in central Illinois, that the center clutch mechanism does
not have a lot to do. The car operates primarily as a FWD car.


Around town I would imagine that is as different matter with revising
and cornering. I would think the center clutch would be pretty busy
determining which wheel(s) need to rotate and provide torque to them
and which ones need to coast.

In normal every day small town driving I would think that that FWD mode
would be more than satisfactory. The clutching mechanism would not need
to be needlessly transferring torque to different wheels for light
driving conditions.

I see the real value of the AWD system when traction is important for
all four wheels and that traction requirement differs for different
wheels. At this point the center clutch and other systems to optimize
the traction to various wheels as needed.

For me this situation occurs primarily in the winter under slippery
snowy conditions.

My question then is there any advantage, during the summer months, or
any harm in inserting the AWD fuse so to disable the center clutching
mechanism and using the car as a FWD car when driving conditions make
the AWD system unnecessary?

 

[bigjim]

The time you need to swerve to avoid something is the time you wish the
AWD kicked in. It helpsa car to grip even in dry especially undr
extreme driving.

 

[Carl 1 Lucky Texan]

I have a 2004 forester automatic. I understand that there is a clutch
mechanism which regulates power between the front and rear wheels.

I am told that under typical driving conditions 90% of the power goes
to the front wheels while the remaining 10% goes to the rear wheels.
This would be essentially a front wheel drive car under usual
conditions with 10% simply rotating the rear wheels.

I would expect that when driving on a straight level highway, as
we have in central Illinois, that the center clutch mechanism does
not have a lot to do. The car operates primarily as a FWD car.


Around town I would imagine that is as different matter with revising
and cornering. I would think the center clutch would be pretty busy
determining which wheel(s) need to rotate and provide torque to them
and which ones need to coast.

In normal every day small town driving I would think that that FWD mode
would be more than satisfactory. The clutching mechanism would not need
to be needlessly transferring torque to different wheels for light
driving conditions.

I see the real value of the AWD system when traction is important for
all four wheels and that traction requirement differs for different
wheels. At this point the center clutch and other systems to optimize
the traction to various wheels as needed.

For me this situation occurs primarily in the winter under slippery
snowy conditions.

My question then is there any advantage, during the summer months, or
any harm in inserting the AWD fuse so to disable the center clutching
mechanism and using the car as a FWD car when driving conditions make
the AWD system unnecessary?

I doubt there is any difference in economy. The car weighs the same and
the driveline will still be moving. Also, the Duty Solenoid 'C' will
have 12v applied constantly instead of being pulsed as normal.

There ARE folks who have put in switches to enable full time 4wd, or
AWD. Those guys mostly do that for offroad, gravel/mud conditions.

Carl

 

[David]

I have a 2004 forester automatic. I understand that there is a clutch
mechanism which regulates power between the front and rear wheels.

I am told that under typical driving conditions 90% of the power goes
to the front wheels while the remaining 10% goes to the rear wheels.
This would be essentially a front wheel drive car under usual
conditions with 10% simply rotating the rear wheels.

I think you've been told wrong. Subaru automatic AWDs used to operate
this way, but my understanding is they went to full-time AWD even on
the ATs many years ago. Many competitors put out part-time AWD
vehicles.

I think your car is 60/40 front/rear torque split by default, but that
may change based on speed or which gear you're in.

My question then is there any advantage, during the summer months, or
any harm in inserting the AWD fuse so to disable the center clutching
mechanism and using the car as a FWD car when driving conditions make
the AWD system unnecessary?

Dunno about harm, but the only advantage is likely to be longer lasting
clutch pack, and those don't seem to be a big failure item anyway.
Fuel-efficiency increase? Not likely to see much if you don't disengage
the axle at the hubs too--you're still spinning the axles & driveshaft
as you drive, just powering them via the wheels instead of the
transmission.

It seems far more useful to add a switch to engage the clutch manually,
than to disable it.

I have a manual with a limited-slip gear-driven center differential,
and there are a couple of times I would really have liked to be able to
lock it up.

 

[Edward Hayes]

Yes; the Forester AT is 60/40 front to rear torque split i.e. default
ratio. You would see no measurable difference in fuel economy using
FWD only. You WILL be putting 100% of the engine torque through the
front differental which is designed for the normal split loading. JMO
Ed Hayes