Which Subaru AWD is Best For Deep Snow (Outback 6-cylinder or 4-cylinder Forester)? - Subaru Forester Owners Forum
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post #1 of 32 (permalink) Old 03-21-2013, 03:47 PM Thread Starter
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Question Which Subaru AWD is Best For Deep Snow (Outback 6-cylinder or 4-cylinder Forester)?

I currently own a 2013 Outback with a 6-cylinder engine and 5EAT 5-speed auto transmission and am considering the 2014 Forester with a 4-cylinder and CVT.

In comparing the two different Subaru AWD systems (6-cylinder in Outback versus 4-cylinder in the Forester), if all things were equal, how would the Forester's 4-cylinder AWD handle in deep snow in comparison to the Outback's 6-cylinder AWD system (which I own)?

I have read that the 6-cylinder AWD normally sends 45% power to the front wheels and 55% power to the rear. 4-cylinder AWD systems send 90% power to the front and 10% to the rear under normal conditions.

Which AWD system is better in deep snow?

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post #2 of 32 (permalink) Old 03-21-2013, 03:51 PM
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The forester with CVT will have a 60/40 power split. Manual will have a 50/50 split.

Are you looking at the forester with or without X-Mode? If the Forester has X-Mode, it would without a doubt be better. Without X-Mode, they would be pretty even in the snow.



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post #3 of 32 (permalink) Old 03-21-2013, 03:59 PM Thread Starter
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Probably looking to add a new Forester Limited or Touring with X-Mode to go along with the '13 Outback which we love.
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post #4 of 32 (permalink) Old 03-22-2013, 06:05 AM
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The 90/10 distribution was on older 4EAT Foresters. I believe the current (well, previous now) SH generation sends 60/40 on 4EAT and 50/50 on 5MT.
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post #5 of 32 (permalink) Old 03-22-2013, 08:06 AM
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"X" mode? wutz that?
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post #6 of 32 (permalink) Old 03-22-2013, 08:28 AM
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"X" mode is the new thing available on the 2014 foresters. Supposed to be similar to Si drive I think, but more computer controlled. Haven't seen write ups on it yet...

2009 XT, Camillia Red Pearl
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post #7 of 32 (permalink) Old 03-22-2013, 10:29 AM
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Originally Posted by 147_Grain View Post
Which AWD system is better in deep snow?
The one with better tires. Honestly, tires will make much more difference than a "soft" 4WD system like the one in a Subaru (or for that matter any crossover SUV / CUV). All these cars rely on brakes to "direct" the torque to the wheel with most traction - some are better then other, but all MUST detect slippage before activating, meaning that some wheels have already lost traction.

If you want ultimate snow / mud performance you need a "hardcore" 4x4 system with locking transfer case and locking differential, like a Jeep Wrangler or Toyota FJ Cruiser / 4Runner / LandCruiser. Only these cars allow to direct up to 100% of torque to a single wheel with traction, without spinning any of the other wheels.

No electronic system can beat locking differentials in a truly deep snow or mud.
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post #8 of 32 (permalink) Old 03-23-2013, 06:24 AM
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Originally Posted by katekebo View Post
The one with better tires. Honestly, tires will make much more difference than a "soft" 4WD system like the one in a Subaru (or for that matter any crossover SUV / CUV). All these cars rely on brakes to "direct" the torque to the wheel with most traction - some are better then other, but all MUST detect slippage before activating, meaning that some wheels have already lost traction.

If you want ultimate snow / mud performance you need a "hardcore" 4x4 system with locking transfer case and locking differential, like a Jeep Wrangler or Toyota FJ Cruiser / 4Runner / LandCruiser. Only these cars allow to direct up to 100% of torque to a single wheel with traction, without spinning any of the other wheels.

No electronic system can beat locking differentials in a truly deep snow or mud.
Actually, Subaru AWD does not require slippage to activate-it is a 100% full time AWD-All wheels all the time, no exceptions. They even designed the new hybrid so that it will always be AWD even if the battery packs powering the rear wheels fail/discharge. Any subaru with an automatic transmission (also the 6 speed manual in the STi) are constantly transferring power, even in situations where there is no slipping. Manual transmissions stay at a 50/50 split, and only transfer when there is slipping.


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post #9 of 32 (permalink) Old 03-23-2013, 06:30 AM
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Originally Posted by katekebo View Post
The one with better tires. Honestly, tires will make much more difference than a "soft" 4WD system like the one in a Subaru (or for that matter any crossover SUV / CUV). All these cars rely on brakes to "direct" the torque to the wheel with most traction - some are better then other, but all MUST detect slippage before activating, meaning that some wheels have already lost traction.

If you want ultimate snow / mud performance you need a "hardcore" 4x4 system with locking transfer case and locking differential, like a Jeep Wrangler or Toyota FJ Cruiser / 4Runner / LandCruiser. Only these cars allow to direct up to 100% of torque to a single wheel with traction, without spinning any of the other wheels.

No electronic system can beat locking differentials in a truly deep snow or mud.

he didnt say which was better for offroading.

try locking your diff's then hitting a patch of dry ground and having to turn..

then some snow 1 mile ahead... then dry....

yea not the best system for on road.

sounds like you havent heard of X-drive either.

IMO AWD is far superior ON ROAD to conventional 4x4 "truck" type systems.

I've had both

4x4 is great but unless you have a center diff. you can have major binding

and dont try turning with front and rear locked you will get really bad handling characteristics on road.

living in ohio you should know this.
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post #10 of 32 (permalink) Old 04-02-2013, 07:10 AM
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Originally Posted by Rand View Post
he didnt say which was better for offroading.

try locking your diff's then hitting a patch of dry ground and having to turn..

then some snow 1 mile ahead... then dry....

yea not the best system for on road.

sounds like you havent heard of X-drive either.

IMO AWD is far superior ON ROAD to conventional 4x4 "truck" type systems.

I've had both

4x4 is great but unless you have a center diff. you can have major binding

and dont try turning with front and rear locked you will get really bad handling characteristics on road.

living in ohio you should know this.
Living in Ohio, owning a vehicle with Torsen central differential and being a mechanical engineer, I know exactly what I'm talking about. I also used to drive a BWM with X-drive, and I am quite familiar with the system

Most AWD vehicles, including Subaru (and BMW), suffer from the same limitation. Torque is distributed to all wheels accordingly to a design pattern (50/50, 70/30, depending on designers preferences and objectives). That means that if one wheel ends up on a slipper spot and traction drops to an insignificant level, the amount of torque going to all other wheels drops proportionally INSTANTLY. Only AFTER the wheel on the slippery surface has started to slip and the computer has detected a difference in rotational speed, the system can intervene and redirect the torque to the wheels with traction. It takes only a fraction of a second, but the slippage of at least of one wheel is inevitable. Some systems are pretty "dumb" and can only deal with one wheel slippage (Honda CRV used to be that way, don't know about latest model), some can deal fine if the loss of traction is in a diagonal pattern (for example Toyota Highlander), some are very smart and can deal with up to three wheels loosing traction (Subary, BMW X-drive, Mercedes 4Matic). But regardless of how smart or dumb the computerized system is, it depends on the difference in rotational speed between tires, and this, by design, implies that one or more tires are slipping and hence are subject to dynamic coefficient of friction vs. static coefficient of friction (which is always higher).

The ONLY exception is a mechanical system based on a Torsen differential. A Torsen has the ability of directing torque based on difference in "resistance" instead of rotational speed. Torsen was first used by Audi in their Quattro system, and is used by Toyota in some of their better off-road vehicles (Land Cruiser, FJ Cruiser, Lexus LX and GX, 4Runner). The downsides of Torsen are:

- cost: a Torsen differential is more expensive than a software based system. All hardware required for a "smart" AWD system are already in place in any AWD vehicle equipped with ABS and electronic stability system. All you need is a little bit of software and you can create a system like X-drive or 4Matic with no additional physical equipment added. A Torsen adds a couple thousand dollars to price of the car.

- fuel consumption - because Torsen is a mechanical system that is always "on", it adds to fuel consumption by creating additional resistance when turning. It does not create any significant difference in driving "feeling" and performance, but adds a few % of extra fuel burn.

A "dumb" 4WD system like used in pick-up trucks and Jeep Wrangler indeed has the inconvenience of being a part-time system that has to be turned off most of the time. But once you get in serious snow, it WILL perform better than most electronics-based systems. With a Torsen, you have the best of both worlds - full-time AWD, plus user-selectable option to switch to "hard" 4WD. But that's why Lexus, Land Cruise and Audi Quattro cost more than a Subaru. You get what you pay for.

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post #11 of 32 (permalink) Old 04-02-2013, 07:33 AM
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how deep ?

You have to say how deep do you mean deep ?

here in parts of the UK we've had 2 feet of snow over the last few winters and my Foresters (2007my and 2012my) both sailed through it, although my current has Bridgestone tyres which are significatly better that the Yokohamas on the old car.

I realise though 2 feet is deep for UK, for others it may be nothing !
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post #12 of 32 (permalink) Old 04-02-2013, 08:55 AM
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Originally Posted by chrisletts View Post
You have to say how deep do you mean deep ?

here in parts of the UK we've had 2 feet of snow over the last few winters and my Foresters (2007my and 2012my) both sailed through it, although my current has Bridgestone tyres which are significatly better that the Yokohamas on the old car.

I realise though 2 feet is deep for UK, for others it may be nothing !
You mentioned the key word - tires. Good winter tires are way more important than 4WD system. A car with basic AWD but good winter tires will easily outperform another car with the best 4WD but summer tires. Tires are more important than the drive system. 4WD (or AWD) will help you with going up hill and starting, but won't make much difference on curves, and zero difference when braking. Actually most people with AWD vehicles tend to crash in winter because of overconfidence.

Here is a video that illustrates the point. A Subaru with all-season tires vs. a Mini with winter tires. The Mini easily beats the Subaru on slalom, high speed curve and braking. The only situation where the Subaru has an edge is stright acceleration.


Now, regarding snow depth. It depends. With fresh, dry snow, you can easily plow through 2 ft of snow. But with wet, "heavy" snow with an ice layer underneath, 4 inches will be enough to cause serious difficulties for most vehicles.
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post #13 of 32 (permalink) Old 04-02-2013, 04:26 PM
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Originally Posted by katekebo View Post
The one with better tires. Honestly, tires will make much more difference than a "soft" 4WD system like the one in a Subaru (or for that matter any crossover SUV / CUV). All these cars rely on brakes to "direct" the torque to the wheel with most traction - some are better then other, but all MUST detect slippage before activating, meaning that some wheels have already lost traction.

If you want ultimate snow / mud performance you need a "hardcore" 4x4 system with locking transfer case and locking differential, like a Jeep Wrangler or Toyota FJ Cruiser / 4Runner / LandCruiser. Only these cars allow to direct up to 100% of torque to a single wheel with traction, without spinning any of the other wheels.

No electronic system can beat locking differentials in a truly deep snow or mud.
A 4WD truck is a horrible vehicle choice for snow. Snowy weather usually comes with roads that are a mix of snow, ice, slush, and bare pavement. In an AWD vehicle, you just drive and the system takes care of it. With a truck, you have to manually go in and out of 4WD constantly as road conditions change.
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post #14 of 32 (permalink) Old 04-02-2013, 06:12 PM
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Here is another good video that illustrates the performance difference between an electronic system and a "real" 4WD system with locking differentials.

The FJ cruiser gets into a deep mud pit and gets stuck. The driver engaged A-Track, Toyota's "intelligent" 4WD system before entering the pit. The A-Track is a pretty smart system that can direct the torque to the wheel(s) with best traction. It works well with one, two and even three wheels loosing traction, as long as one wheel has good contact with the ground, this wheel get all the torque. Nevertheless, he gets stuck. It can't be seen clearly on the video, but the rear, right wheel is the only one that is not spinning. The computer tries to direct as much torque as possible to the only wheel with traction, but this is not enough to get the vehicle out of the mud. And then, right after approx. 1 min of the video, the driver locks the differentials and the "miracle" happens - the FJ gets out of the mud pit easily.

So what's the difference? The difference is in the static vs. dynamic coefficient of friction. Static friction is always higher than dynamic friction. As soon as one wheel starts spinning in mud or snow, it contributes with almost zero forward force. Even if one wheel has relatively good traction, it's not enough to push the vehicle through the heavy terrain. With three wheel spinning, you basically have only 25% of the total available force to push the vehicle forward. By locking the differentials, you get 100% traction because all the wheels are stationary and rely on static (instead of dynamic) friction to push the vehicle. This is why all serious off-road vehicles (and military ones) have "lockers" - central, rear and sometimes front.

So why car manufacturers rely on electronic torque distribution system instead of using a "simpler" mechanical system? Because lockers require much stronger components. Basically, a single wheel (CV joint, axles, etc.) has to be able to take 100% of engine's torque. If three of the wheels loose traction and the differential are locked, 100% of the torque and power will go to the only wheel that still has traction. In an electronic system this won't happen. Even if three wheels are locked by the brakes, the torque is still distributed more or less evenly - 1/4 goes to pushing the vehicle forward, 3/4 is absorbed by the brakes. You can see the implications by comparing the size of the different drivetrain components between an AWD vehicle and a "hardcore" 4WD one. I am quite familiar with Toyota Higlander and the FJ Cruiser. Both weigh about the same (4400 lb, give or take 50 lb) and have 270 hp engines. Yet, FJ Cruiser's differential is just over 8 inches (203 mm), and Highlander's differential is only 6 inches. The CV joint in the FJ is at least 50% bigger diameter than Highlander. Rear wheel bearings in the Highlander are 60mm diameter, and 90mm on the FJ.

There are some excellent electronic AWD systems - Mercedes' 4Matic, VW 4Motion, Subaru's "symmetric AWD". But when you really need ultimate performance in sand, deep snow or mud, nothing beats "lockers". But they are expensive (not the lockers themselves, but the consequences they have on the drivetrain design).
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post #15 of 32 (permalink) Old 04-02-2013, 07:03 PM
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Here is another good video that illustrates the performance difference between an electronic system and a "real" 4WD system with locking differentials.
Fj cruiser Mud Pit - YouTube

The FJ cruiser gets into a deep mud pit and gets stuck. The driver engaged A-Track, Toyota's "intelligent" 4WD system before entering the pit. The A-Track is a pretty smart system that can direct the torque to the wheel(s) with best traction. It works well with one, two and even three wheels loosing traction, as long as one wheel has good contact with the ground, this wheel get all the torque. Nevertheless, he gets stuck. It can't be seen clearly on the video, but the rear, right wheel is the only one that is not spinning. The computer tries to direct as much torque as possible to the only wheel with traction, but this is not enough to get the vehicle out of the mud. And then, right after approx. 1 min of the video, the driver locks the differentials and the "miracle" happens - the FJ gets out of the mud pit easily.

So what's the difference? The difference is in the static vs. dynamic coefficient of friction. Static friction is always higher than dynamic friction. As soon as one wheel starts spinning in mud or snow, it contributes with almost zero forward force. Even if one wheel has relatively good traction, it's not enough to push the vehicle through the heavy terrain. With three wheel spinning, you basically have only 25% of the total available force to push the vehicle forward. By locking the differentials, you get 100% traction because all the wheels are stationary and rely on static (instead of dynamic) friction to push the vehicle. This is why all serious off-road vehicles (and military ones) have "lockers" - central, rear and sometimes front.

So why car manufacturers rely on electronic torque distribution system instead of using a "simpler" mechanical system? Because lockers require much stronger components. Basically, a single wheel (CV joint, axles, etc.) has to be able to take 100% of engine's torque. If three of the wheels loose traction and the differential are locked, 100% of the torque and power will go to the only wheel that still has traction. In an electronic system this won't happen. Even if three wheels are locked by the brakes, the torque is still distributed more or less evenly - 1/4 goes to pushing the vehicle forward, 3/4 is absorbed by the brakes. You can see the implications by comparing the size of the different drivetrain components between an AWD vehicle and a "hardcore" 4WD one. I am quite familiar with Toyota Higlander and the FJ Cruiser. Both weigh about the same (4400 lb, give or take 50 lb) and have 270 hp engines. Yet, FJ Cruiser's differential is just over 8 inches (203 mm), and Highlander's differential is only 6 inches. The CV joint in the FJ is at least 50% bigger diameter than Highlander. Rear wheel bearings in the Highlander are 60mm diameter, and 90mm on the FJ.

There are some excellent electronic AWD systems - Mercedes' 4Matic, VW 4Motion, Subaru's "symmetric AWD". But when you really need ultimate performance in sand, deep snow or mud, nothing beats "lockers". But they are expensive (not the lockers themselves, but the consequences they have on the drivetrain design).
Lots of good info in your post. I'd like to add one more to your list of hardcore 4WD - the Xterra. With a two speed transfer case, locking rear diff, ABS traction control up front, and a set of v-bar reinforced ladder chains on the rear, it also does a pretty fine job when the snow gets deep.
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