Thread: Subie AWD question

Quick question:
Would you do any damage to your subaru by disabling the AWD for the summer? I imagine you would get better gas mileage. Someone here must know something about this.

the only thing I can think of is uneven tire wear which I hear is not good for AWD systems.

Originally Posted by pointedem

Quick question:
Would you do any damage to your subaru by disabling the AWD for the summer? I imagine you would get better gas mileage. Someone here must know something about this.

the only thing I can think of is uneven tire wear which I hear is not good for AWD systems.

Disabling, as in pulling the fuse, so it would be stuck in FWD???

Kinda.
you put a fuse into the FWD slot.

I read a bit about it on scoobymods.com (I think). Can't do it on mine as it only applies to automatics. Over there they seemed to have no problem with it.

edit Read some more over there about it and it seems they aren't that supportive. Go over there and do a search for FWD and fuse together and you'll get quite a bit on it. Apparently it's even in the manual in respect to doing it temporarily while running an undersized spare.

Tried it on mine. Didn't realy get any better gas millage. Did handle funny when I pushed it hard. Would spin wheels when it shouldn't.

Does it rain where you are? are there curves where you are? To pick up 1-2 MPG and loose handling? Doesn't seem worth it.

I thought subie AWD was purely mechanical, ie no fuse to disable it like on a skyline or evo.
Phil, am I totally wrong?


hijack /Phil, Ive got an 04 wrx w 41k miles, should I be using synthetic oil? /end hijack

I considered this last year, and did some research. I decided against it, though, when a mechanic simply said "hey, if they wanted you to do it, why wouldn't they put in a switch and advertise it?" And since most say the mileage gain ain't that much......

I don't want to give the engineers who designd the system too much credit but I've got to believe there is a certain gestalt to the design that maximizes efficiency. For example if you disable the rear wheel power is the rear dif and drive shaft are spinning but not delivering power, does that use energy unproductively? If power is diverted at the transmission (or transfer case equivilant don't know the correct term) does that increasing drag on the rear wheels (as opposed to a standard rear axle on a fwd car).

Originally Posted by skiingsamurai

I thought subie AWD was purely mechanical, ie no fuse to disable it like on a skyline or evo.
Phil, am I totally wrong?


hijack /Phil, Ive got an 04 wrx w 41k miles, should I be using synthetic oil? /end hijack

Manual trans = totally mechanical

automatic = you totally wrong

huh, so im right and wrong. Interesting. No wonder so few WRx owners talk about it. (not many AT's)

cool thanks for the heads.

Flexon Phil- we have seen almost no rain since May and I drive in a straight line to work. Boring, I know.

pointedem - what year/model? Most of the automatic subies are actually biased at 90-10 on the center differential. The manuals are biased at 50-50, but in the automatic I think they went 90% to the front in order to optimize fuel economy since you don't have good control of your gearing and throttle. (That will also explain why the automatics understeer a lot more than the manuals). My understanding is that the manual and automatic center transfer/clutch systems are different. If you have an automatic, you can see that it will make little difference. If you have a manual, then I would check on L7's reference.

My opinion is that the point of the fuse is for towing when you don't have a flat-bed or a dolly tow and you need to run on one pair of wheels, and not for driving the vehicle around. When driving a vehicle, you impart mechanical stress on the drivetrain and if it's not designed to do what you want to then bad things can happen. My best guess is that it's not a good idea and that putting in that fuse should give you little-to-no discernible fuel economy increase unless you are driving in a straight line at 55 mph without stopping or accelerating, but that's just a guess

right on thanks for the input.

LGT 02. auto.

just chiming in to say this all sounds correct.
The auto's (other than turbo'd models and the Tribecal) are about 90/10 power split.

My Subie Mechanic told me never to insert that fwd fuse unless I absolutely had to be towed without a flatbed. He also said that driving it over 25mph in fwd could do serious damage.

Also I am pretty sure it is a 60/40 split on the autos, not a 90/10, as per my mechanic who does Subaru race stuff as well.

Originally Posted by pointedem

cool thanks for the heads.

Flexon Phil- we have seen almost no rain since May and I drive in a straight line to work. Boring, I know.

I assume that is a picture of your kid for your avatar...Why would you risk loosing some security of AWD if he will be with you. Do you have to make lane changes?

Here is a question..do you have fire insurance on your house? Have you ever used it? Are you going to cancel it?

Originally Posted by Flexon Phil

I assume that is a picture of your kid for your avatar...Why would you risk loosing some security of AWD if he will be with you. Do you have to make lane changes?

Here is a question..do you have fire insurance on your house? Have you ever used it? Are you going to cancel it?

AWD doesn't offer security in the rain, although it can be a lot of fun to do 4 wheel slides.

As everyone on here knows, AWD does offers security in the snow.

Implying that cars without AWD are more dangerous than other vehicles and then citing lane changes as an example is misleading.

Hijack over.

On topic response: Talked to my bro who's a subie nut and has also been involved with a number of racing efforts. The rest of the thread seems spot on.

Originally Posted by SpinalTap

AWD doesn't offer security in the rain, although it can be a lot of fun to do 4 wheel slides.

As everyone on here knows, AWD does offers security in the snow.

Implying that cars without AWD are more dangerous than other vehicles and then citing lane changes as an example is misleading.

Hijack over.

On topic response: Talked to my bro who's a subie nut and has also been involved with a number of racing efforts. The rest of the thread seems spot on.

Absolutely it does. One example: If you are excellerating into traffic and the weight of the car is transfered from the front to the back, with an AWD you still have the weight over drive wheels. Two: Drive a 2wd car and a AWD car in torrential rain, you can't tell me that a (comparable) 2wd is handling as well as the AWD.

Its not that AWD cars are safer than a 2WD car there is much more to safety than the drive system...its that a car that is designed to be AWD and if you start disabling systems, you throw the balance of the car off.

If you drive a suby over 25 or so in FWD, I would not want to imagine the damage occuring to the center diff trying to displace wheelspin. On the WRX and other manuals, it is possible to make the car RWD by running a welded center diff and removing the front axles and plugging them. However, the rear diff, most commonly an R160, is now recieving twice the strain under normal conditions and even more under a launch than it ever had before. The diff pops quite often when modded in this manner. The R180 out of an STi is more capable of handling the abuse, but you need to run the STi axles and driveshaft and rear brakes unless you swap hubs.

bottom line, leave a suby a suby.
Also, in your 02, the car goes into "limp mode" with awd disabled. it will only go to 2000 rpm and not above a certain speed. your a/f will be fucked and the car will run horribly. If you have the turbo model, a nice ECU flash will pick up 3-4mpg while making the car more fun to boot.

Originally Posted by skiingsamurai

hijack /Phil, Ive got an 04 wrx w 41k miles, should I be using synthetic oil? /end hijack

Yes. 5w-30 or 10w-30 in colder weather, and 15w-50 in the summer if it gets really hot where you are. Very important for oil life with the turbo. You may also want to try synthetic in the gear box, I had very good luck with redline superlight shockproof.

This is coming from someone who owned a '02 wrx and '04 STi. 350 whp on the STi...

Originally Posted by Flexon Phil

Absolutely it does. One example: If you are excellerating into traffic and the weight of the car is transfered from the front to the back, with an AWD you still have the weight over drive wheels. Two: Drive a 2wd car and a AWD car in torrential rain, you can't tell me that a (comparable) 2wd is handling as well as the AWD.

Second the Absolutely! AWD even improves handeling on Dry Pavement! This is why Audi Quattros have been banned from most forms of road racing... the Quattro gave drivers an unfair advantage Bottom Line is that a wheel with power to it has like 75% more traction than a wheel without power. An AWD car has a lot more traction than its 2 wheel drive counterpart!

Going to have to disagree with you on one thing... An AWD car is absolutley safer than a 2WD car. An AWD car has the most forgiving handeling characteristics of any other set-up... ever kick the tail out too far and spin out on a RWD car? Its much harder to do on an AWD cars. Ever expierience Torque Steer on a FWD car? Not fun. Some AWD cars like Audi Quattros have superior braking capabilities due to the AWD drivetrain. (Subys disconnect the AWD for Braking)

Most Subys have a Viscous Coupling in the Center Diffy, this means that under normal circumstances you are driving a FWD car with very little power going to the rear (and very little drivetrain drag to worsen your MPGs) its only when the front wheels start to slip that power get transfered to the rear wheels in any appreaciable amount. The Audi Quattro is one of the few AWD cars that actually gives you about 50%-50% Front to rear under normal driving circumstances, then the Center Diff can Bias Front to Rear as much as 80%-20% when needed.

Originally Posted by 300hp

bottom line, leave a suby a suby.
Also, in your 02, the car goes into "limp mode" with awd disabled. it will only go to 2000 rpm and not above a certain speed. your a/f will be fucked and the car will run horribly. If you have the turbo model, a nice ECU flash will pick up 3-4mpg while making the car more fun to boot.

You seem to know what you are taking about. weird thing is that I ran my car for 2 days ( until new tires were put on) w. the FWD fuse in there. Drove fine, 60mph on highway and def. reved above 2krpm. Car ran fine.

If it is so bad for the car, why on earth would it say in the user manual that this is what you are suposted to do when you need to run your spare.

Just curious.
I have the 2002Legacy GT, no turbo.. 2.5l

right. If no turbo, then it's not the gt. You basically have the same car as me then, I have an 03. I also ripped open the exhaust on a piece of rebar up in the mountains, but we're not talking about that now (insurance is good, just the cat is 500 bucks).

BUT, it also says in your owners manual, that you shouldn't drive over 50 with a donut, i think that's about 2 revs.

no no I have the LGT ltd.
Are you thinking about the XT?
http://www.cars101.com/subaru/legacy/legacy2002.html