As one would suspect, a good driver can do more with less when rock crawling. That said, ground clearance, locking differentials, suspension travel, and appropriate tires all play their part, and probably in that order of importance.
98 Subaru Legacy wagon with AWD and has a fuse box up under the hood on the passenger side where you an INSERT a fuse to DIS-ABLE the rear wheel drive part.
Run of the mill retired folks puttering around see very little difference in MPG or tire wear.
Just a very small difference in long / fast interstate miles.
YMMV
It’s been pretty much covered by others, but I’ll add this. Manufacturers can offer AWD systems that vary greatly from one model/brand to the next. My former car, a Subaru Outback, had an AWD system that delivered power to all 4 wheels all the time, with sensors to detect a wheel spinning, so that torque could be redirected to other wheels.
My current vehicle, a Honda Ridgeline, has an AWD system that operates mostly in 2WD mode (front drive) until it senses a front wheel spinning. Once slippage is detected, it redirects torque to other wheels, bringing the rears into the mix. On the Ridgeline, I have the option, via a dash mounted button, of “locking” the rear differential, which locks a version of 4WD in place, but only on loose or slippery surfaces, and only at a very slow speed. I think if I exceed 18 mph, the diff lock kicks off.
All this to say that there are dozens of flavors of the systems being marketed as “all wheel drive”, and it’s your best interest to study up on the exact nature of YOUR potential vehicle.
It won’t make any difference at all.
With the drivetrain layout on a Subaru, it makes no difference whether any power is actually going to the back wheels or not. The FWD fuse is there on models with the electronically-controlled center differential, even the subtle difference in circumference between the compact spare and normal worn tires can cause problems with the differential. There might also be some situations where you’d want to put the car on a 2 wheel dynometer, and the fuse allows that too.
But you don’t want to drive around with the fuse in all the time. In theory, driving around with the FWD fuse in could cause premature failure of a solenoid in the center diff that’s normally off but is locked on with the fuse. Replacing that solenoid requires removing the transmission. Granted, lots and lots of Subaru drivers over the years have had this same “bright idea” and it hasn’t caused an epidemic of center differential failures, but it’s still a very very bad idea.
Not only that, but most of the fuel economy differential is due to the extra weight of the transfer case, driveshaft, and assorted gubbins. None of that magically disappears when you take the fuse out.
How much does a gubbin weigh?
Twice as much as a widget, but less than a doobry. 
I should have said drive shafts, since there’s a longitudinal shaft plus two extra wheel shafts.
Well, with most AWD cars there’s also the issue that there’s much more driveline losses for power going to the rear axle than power going to the front axle. They’re based on the usual FWD car layout where the engine is mounted transversely directly above the transaxle and front wheels. This layout works great for FWD because it can transmit power to the the drive wheels without any 90 degree turns in the drivetrain, but to also send power to the rear it requires two extra turns. So the less power you send to the rear, the more efficient the car is going to be which is why most car-based AWD systems are heavily front-biased, or only send power when wheel-slip is detected.
Subarus, on the other hand, have the engine mounted longitudinally in front of the front wheels, which they can do because the boxer engines they use are really short. This means that power going to the front and rear both make only one 90 degree turn, so the driveline losses are pretty similar. That’s how they achieve the vaunted 50/50 AWD while still getting okay fuel economy, but it also means that forcing the power split device to send all the power to the front axle (which is what happens when you plug the FWD fuse in) has essentially no effect on fuel economy.
Most Subarus, actually pretty much all of them these days, do not have a center differential and do not transmit transmit power equally front to rear, a mostly meaningless statement anyway on a car without a center differential and thus no way to split torque between two axles without clutch lockup and drivetrain bind when the steering wheel is turned.
Unless your Subaru is a 1) manual transmission or 2) a 3.6 H6l with the 5 speed automatic or 3) a rare older Outback with the 4EAT plus VTM planetary center differential, then it does not have a center differential and is no different than any other system that uses the “slip and lockup clutch” method.
This is the reason why manual transmission Subarus which do have center differentials and thus “full time” AWD get significantly worse fuel economy than automatic transmission versions of the same vehicle, or the same fuel economy using a 5 speed manual box vs the old, rather inefficient JATCO 4 speed automatic when other vehicles from the same era will have a significant fuel economy advantage with the manual box. Subarus with automatic transmissions also have virtually no fuel economy penalty vs even FWD competitors int he same class. It’s because the automatics are all “part time” AWD. The fuse to “disable” AWD only exists on the automatic cars, where they simply prevent the center clutchpack from engaging. It doesn’t “force” the engine to do anything. On manual transmission vehicles with a mechanical center differential there is no fuse as there is nothing to disable. There is no fuse to make a WRX STi or Audi RS5 FWD.
You should be very wary of anyone trying to convince you of the merits of “the Subaru AWD” system as if there is only one system or that Subaru systems are somehow unique.
It’s basically been said by others, but here’s my take on it. For driving around paved roads in inclement weather (think deep snow before plowing), I’m happy with my Forester. For driving on generally good dirt roads with some mud or snow issues, I’m happy with my Forester. For something where I’m sure chaining up will get me out of it, I’m happy with the Forester. For true off-road work, dirt roads in really inclement weather, and other such cases, I’d want true 4WD. Since I’ll almost never drive in those conditions, I’m happy with the Forester and didn’t see a need to buy something like my father’s 4Runner. I’d be okay with something like it, but at the time I bought the Forester I was in upstate NY and looking for something I could use in the snow without being interested in off-road use. The Forester I bought was a good compromise of several requirements and wants I had at the time.
Yes, there’s different systems, but that’s really just pedantry. The viscous coupling center differential AWD Subarus and the electronic transfer clutch AWD Subarus are, at least for the normal snow-country driver, functionally identical. They both send power to the front and rear axles in roughly equal proportions (yes, many of the non-VC ones are really 60/40. You got me!) and can alter the ratio to go around corners on dry pavement. What else do you want?
And I completely stand by the blanket statement that Subarus are better in terms of foulweather handling than any other inexpensive AWD cars. Yes, “the Subaru AWD system” is really multiple systems, but as I mentioned above it’s not that the power-split devices they use are of any great mechanical genius, it’s that their funky drivetrain layout is uniquely suited to AWD.
Also, what are you talking about with the manuals? Only in the most recent Subaru models have the VC-equipped manuals gotten worse mileage than the transfer-clutch equipped automatics, but that’s only because the automatics have gone to CVT’s (and many of the manual models still have 5 speeds with infuriatingly low 5th gears.)
Because the point of a center differential is to proportion torque equally to both axles so that since each axle is only getting half the torque, wheel slip is less likely to occur especially during things like turns when the tires need traction to both turn and accelerate(or brake). With no center differential the only thing the drivetrain can do is either lock up the axles, or not. Locking up the axles is not a dynamic torque split, it’s just forcing both axles to turn at the same speed regardless of traction. SO what happens when you turn the steering wheel and the clutch is locked, like when you’ve got 4 low engaged in a truck? The drivetrain binds, which is why there’s a clutch there in the first place and not a fixed PTO. When do you often need to transfer torque because one or more wheels lose traction? How about when you turn? This is a non-trivial difference between real full time AWD and part time on demand AWD that Subaru’s marketing literature makes very clear, while strongly implying that Subarus are of the former variety when the opposite is in fact true.
You seem to be strongly implying, without outright saying it, that somehow a longitudinal engine layout is somehow superior for the purposes of AWD. This is simply not true. 1) There are plenty of vehicles that using a transverse engine with full time mechanical center differential AWD. The current AWD Toyota Sienna minivan for example, or the Mitsubishi Lancer Evolution, all the old 1990s AWD hot hatches and rally homologation specials - Celica GT4, Nissan Pulsar GTiR, Mazda 323 GTX, Lancia Delta Integrale, etc., The old DSM triplets (Mitsubishi Eclipse, Eagle Talon) and the mechanically similar Dodge Stealth/Mitsubishi 3000GT, Afla Romeo even had a sedan (159? 164?) that had a transverse drivetrain with a Torsen center differential. So there is no reason you can’t have any kind of AWD you want with any kind of drivetrain layout. Most of these no longer exist, because there is little market demand for these kinds of full time AWD drivetrains with their accompanying fuel economy penalty. Again 90% of Subarus are not full time AWD either, so it’s largely irrelevant.
So then now that we have established that drive train orientation has no impact on the type of AWD system used, then what advantage does a longitudinal drivetrain have? First of all Subaru isn’t the only one to use a longitudinal FWD packaging, Audi obviously does too, but here’s the thing - most Longitudinal Audi sedans are FWD, except in the US market where Audi is only a minor player. The “advantage” of having a longitudinal engine entirely ahead of the front axles is the same as the Porsche 911 having it behind the rear axle - the massively lopsided weight distribution puts a whole bunch more weight on the driven wheels than the non-driven wheels, so a RWD 911 is probably marginally better in the snow than a RWD Cayman, and a FWD Audi/Subaru is marginally better than another FWD car with a more balanced weight distribution, at the expense of much more compromised driving dynamics and an ungainly dash/axle ratio.
There really aren’t that many new ideas these days as far as basic car layout is concerned, it’s all pretty well understood, and in any case many other car companies have tried Subaru’s layout in the past as well. If there were any advantage to it they would all be using it. They aren’t. Sometimes most people do a thing one way because it is actually the best way.
Read it again. Leave out the modern CVT ones if you want and just compare the old manuals to the old 4ATs, the CVTs have the same AWD drivetrains as the 4ATs.
Good to hear as I got the Impreza hatchback and hope it will get me up my driveway a lot better than the 2WD Corolla did!
It is an automatic Sport Premium with the option to go into a “manual” mode with those paddles and go into super low gear which I plan to do down snowy hills. I’m assuming that has no effect on the all-wheel-drive-ness?
I think you’re massively confused about how the transfer clutch style AWD system works. It’s not just an AWD on/off switch. The computer can adjust the amount of pressure on the clutch pack to control the amount of power going to the rear axle. By default, at least on newer Subarus, it’s close to 50/50. The computer detects when the car is going around a corner and sends more or less power to the rear accordingly. It’s a “reactive” system in the sense that the computer uses data from the wheel sensors to control the amount of power going to each axle, but it’s mostly just doing electronically what a center differential does mechanically. There’s minor differences in how the systems react in different situations, but broadly speaking they behave pretty much the same. It’s not at all like what we normally call a “reactive AWD system” in the sense of normally FWD, but capable of sending power to the rear axle when wheel slip is detected.
Your list of gas guzzling transverse-engine AWD cars underscores my point. Of course transverse AWD is do-able, you just pay a very steep price in terms of fuel economy for any power you send to the rear axle. For a high performance variant of a FWD econobox, that’s not that big of a deal. For the actual econobox itself it is. You couldn’t make a transverse engine equivalent to Subaru’s economy cars and maintain both the passable fuel economy and the near 50/50 default power split.
(Also, incidentally, you’re wrong about the Previa. It’s normally 100% FWD, but has a reactive AWD system that can go up to 50/50 and it has a manual override that can lock it at 50/50 below 25 MPH.)
The reason why most cars use transverse drivetrains is because it’s very efficient for front wheel drive. The longitudinal layout can work okay for FWD, but it has more driveline losses (to the front), the weight distribution issues you mentioned, and for normal inline engines it makes for really difficult to service engine compartments. The reason why Subaru and sometimes Audi uses it is because good AWD systems are a big part of both of those brands. Subaru is obviously all AWD now (BRZ and JDM stuff excepting) but the Quattro cars are important enough to Audi that they’re willing to make the tradeoff of less efficient FWD cars for better performing AWD ones. Even if they do sell more FWD versions of those cars. Most car makers sell vastly more FWD cars, and for their purposes a reactive and/or heavy front-bias AWD system tacked on to a transverse drivetrain that’ll get people out of their driveways is good enough.
Well, can you point to some examples? With every pre-CVT Subaru model I’m seeing on fueleconomy.gov, the manual gets about as good or slightly better than the automatic. Of course even if there are a few where the auto does slightly better, that’s true of plenty of similar 2wd cars, simply due to differences in gearing.
I used to have a Grand Cherokee with 4x4 and my sister currently has a Ford 500 with AWD. The Jeep was better with mud, and more “offroad” situations. In snow, both were about the same. The ground clearance made a difference, but if you are looking at an SUV, it shouldn’t be a problem. Unless you need to drive up a mountain in the snow, AWD would most likely be fine.
She prefers her AWD (no shifting) and I preferred having shift on the fly 4x4 with low range, for the few occasions I needed it.
FYI, the current Grand Cherokee has 4x4 with no low range (AWD essentially) as standard in the Laredo trim, and optional 4x4 with low range. 4X4 with low range is standard on the Limited, Overland, and Summit.
Part time 4wd if you go off road, AWD if you want a bit more safety in most driving conditions.
Part time 4wd requires significantly more driver involvement in most on-road conditions and it also tends to limit the assistance that both ABS and traction control can provide you. As an example, with part time 4wd while going down hill in slick conditions compression breaking will tend to cause the rear wheels to lose traction as they have less weight and traction. When this happens the rear tires will slide and as they are now traveling faster they will want to be in the front. To avoid this situation you need to actively disengage 4wd when going down hills. Modern AWD systems tend to have limited slip differentials in the transfer case and traction control systems which can correct for this behavior. It is impossible for these systems to compensate in a part time 4wd system as the transfer case is locked and thus at least one of the the front and rear wheels will have to spin at the same speed. To be honest proper tire selection is far more important than AWD/4wd is but IMHO if you have to ask which is better AWD is, you would know if 4wd is needed.
I say this as an owner of a Jeep Wrangler unlimited with 4wd. I have several decades of experience in off road driving and snow driving. This year I have driven both the Mojave road (~140 miles of dirt) and to the arctic circle via the Dempster this past December. While driving the 458.3 mile long Dempster road in slick conditions I would have preferred to have an AWD system as it required a significant amount of attention and manipulation to drive safely with a 4wd vehicle. That said in “it is hard to even walk down” off road conditions I would never want AWD.
A differential and a clutch are two different things. When two wheels are attached to a differential they can spin at different speeds while both receiving torque. In such a car the torque at both the front and the rear can be slip full time. You can’t replace the pumpkin in the back of a truck with a clutch. Without a differential you cannot have full time torque distribution, unless your Subaru has no steering wheel and traveled only in a straight line.
Incidentally, the new Ford Focus RS uses a fixed PTU to the rear axle, and then two sets of clutches, one to each rear half shaft, in the rear differential. In this way you could, I think, have power continuously to both rear wheels while still allowing them to turn at different speeds when turning. So that’s probably one way you could have “full time” AWD without a center differential, if I’ve understood the FOrd press releases correctly.
Subarus with actual 50/50 full time AWD still do get substantially lower fuel economy than similar FWD cars.
I was thinking of the last generation model then.
We have gears that can transmit power at angles. It’s not a problem. Carmakers don’t design the entire car around the orientation of a single gearset.
A 5 or 6 speed manual that gets as good or slightly better fuel economy as an ancient 4 speed torque converter automatic is not par for the course. Surely you must realize this.
Seriously, just read this: Subaru all wheel drive explained - How it works
Describing the multiplate clutch packs Subaru uses as “a clutch” is a gross oversimplification. It’s a series of clutches actuated with the variable hydraulic pressure provided by the transmission. It can provide a wide range of torque splits. The older ones were front-biased but the new ones are 60/40.
The only reason why the manual transmission cars get center differentials instead is because the transfer clutch system relies on the automatic transmission fluid pump.
All Subarus get somewhat lower mileage than equivalent-sized FWD cars. They’re AWD cars. But if they were transverse-based 50/50 full time AWD they would get substantially worse. There’s no economy-oriented cars like that to compare them to because nobody makes them.
Although, now that you mention it, Subaru has seriously closed the gap on fuel economy with FWD cars in recent years. They’ve done this while simultaneously moving to more balanced AWD systems on the automatics.
I won’t claim encyclopedic knowledge of Toyota minivans, but I’m pretty sure the Previa’s AWD system has always been similar to the Rav-4, which (at least in recent iterations) has been a reactive system.
We do have those gears, but they’re more complex and accrue more rotational losses than gears turning on the same plane. The beauty of the transverse layout is that it avoids any of them IF you’re only sending power to the front wheels.
Yes, but I’m not seeing that the difference in fuel economy between late 90’s/2000’s era torque converter transmissions and late 90’s/2000’s era manual transmissions is different for Subarus than it is for any other car.
Also, the center diff in a manual Subaru (at least my WRX) is a limited slip diff. Limited slip is often accomplished with, you guessed it, clutches.
Look at a youtube video of how a differential works I guess? Why do you think the WRX STi has both a mechanical center differential and an electronic multiplate clutch? Same for the Audi RS5.
I don’t know what you are arguing any more.
I already explained why this is.
The Sienna from 2006-2010 used a full time system with a mechanical diff. After that they went to a clutch. The Previa you’re thinking of that did come with AWD was a RWD based vehicle. Later iterations were FWD only AFAIK but they weren’t sold in North America so whatever.
Respectfully, since you are the one making this claim, I will leave it to you to back it up with some sources.
So what, you want evidence that most cars equipped with both a 4 speed automatic or a 5 speed manual will get better fuel economy in the manual version? Fine, although I’m starting to doubt your goodwill on this, let’s go randomly click some butans. Here, 2009 Chevy Cobalt, 27mpg for the 4 speed auto, 29mpg for the 5 speed manual. Why do you think Subaru is an exception to this?
GO read the link, WRX manual transmission is a mechanical center differential with a viscous coupling differential lock. You may also benefit from a youtube video explaining what a differential is.
At this point it’s probably easier to say that anyone who owns or drives a Subaru is almost certainly less knowledgeable about AWD than the average population.