Quick question.

"Alex B" (alexb420) 08/05/2014 at 15:44 • Filed to: None

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Is Subarus Symmetrical AWD bias towards FWD or RWD? I'm assuming FWD for economy, but I'm not entirely sure.

norskracer98-ExploringTheOutback > Alex B 08/05/2014 at 15:48

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My mom has an Impreza, and I have no freaking idea. Its a great system that makes it fun and really amazing to drive.

area man > Alex B 08/05/2014 at 15:51

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FWD

6cyl > Alex B 08/05/2014 at 15:53

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Symmetrical AWD. Shouldn't that be evenly balanced?

Aaron M - MasoFiST > Alex B 08/05/2014 at 15:53

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All and both, depending on the car. An STi is rear-biased, many of the manual cars are 50/50, and the CVTs and automatics can be front-biased, but don't have to be.

Also worth noting, once the running gear is in place the actual power bias doesn't particularly affect fuel economy...the reason front-biased systems in CUVs are better for fuel economy is because they are much simpler and weigh less.

Here's a more complete answer to your original question: http://www.awdwiki.com/en/subaru/

WRXforScience > Alex B 08/05/2014 at 15:53

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It is symmetrical (50/50), except in the STi and anything with the dccd (driver controlled center differential).

The awd behaves similarly to FWD, but minimizes certain drawbacks (torque steer, front tire strain, etc.).

4age20vsilvertop > Alex B 08/05/2014 at 15:55

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Given that all non-AWD Subarus are either FWD or RWD, I'd say SWD.

samssun > Alex B 08/05/2014 at 15:55

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They're all proper longitudinal setups, rather than fwd with a power takeoff to the rear, but the default split depends on the car and transmission, from 50-55% rear on family cars up to 60% rear on the STI.

Correction: looks like the CVTs send 40% to the rear by default.

MonkeePuzzle > Alex B 08/05/2014 at 15:55

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depends, which subaru, and have you pushed the button...

...or rolled the knob?

Lumpy44, Proprietor Of Fine Gif > Alex B 08/05/2014 at 15:59

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I know the Lancers AWC system is 60% front and 40% rear. Subaru could be the same.

HammerheadFistpunch > Alex B 08/05/2014 at 16:07

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I wish I had more time to give you the long answer but the short answer is front wheel drive. in almost all Subarus the front differential is directly geared to the output shaft of the transmission, and then the output shaft from the transmission goes to a power take-off or transfer case. the transfer case will have clutches or a viscous coupling unit in there that will direct the power to the rear as needed. it's slightly more active than typical PTO systems, but the front differential still gets the majority of the torque most of the time

desertdog5051 > Alex B 08/05/2014 at 16:19

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Mine is biased toward the front. I do have the ability to disengage the rear drive to get better mpg on highway trips.

Alex B > HammerheadFistpunch 08/05/2014 at 16:30

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Thanks. Good enough explanation for me!

Delusion77 > Alex B 08/05/2014 at 17:12

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Like some others have said, its not so simple. Depending on what model and transmission you have the AWD system will be different.

Their most basic system is found on their manual transmissions, having a 50:50 split with up to 80% of power shifted towards the front or rear depending on the situations. It uses a viscous center diff however only the performance trim levels (XT,WRX,GT,3.6R etc) have rear LSDs.

Their CVTs will split torque the same way their 4speed auto did, 60:40. Using a sort of electronic clutch in the center. There is a lot more complicated traction control and prediction involved in this system vs the mechanical technique mentioned above. Only the Outbacks have rear LSDs.

Their "premium" ATs found on the WRX, Legacy GT, and Forester XT uses a system called VTD. This has a central planetary gear as well as the electronic central clutch which split the power 45:55. I believe all vehicles with this system have rear LSDs.

The last of the modern AWD systems from Subaru is in the STI. Its the only system to include a LSD in the front as well as the rear. It is the best system Subaru has to offer with a complicated central diff combining the technology used in VTD with a 6speed MT. The split is 41:59 by default but can be adjusted by the driver hence the name DCCD (driver controlled central differential).

Alex B > Delusion77 08/05/2014 at 17:25

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Sounds good. Thanks.

Racescort666 > HammerheadFistpunch 08/05/2014 at 19:15

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I had a whole comment written up but then I found this: http://m.awdwiki.com/en/subaru/

You are correct for the autos, but not the manuals.

Also, I believe subaru's symmetrical branding is in regard to left/right symmetry although nothing has come right out and said this.

HammerheadFistpunch > Racescort666 08/05/2014 at 19:53

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Thats a cool find, but having actually put my hands on the guts of a subaru 5MT and transfer case, I'm pretty confident in my assessment

"symetrical" is branded as a layout, not in terms of traction. its "symetrical" because the driveshaft is inline with the vehicle center-line and the engine center-line. only.

Racescort666 > HammerheadFistpunch 08/05/2014 at 23:35

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As have I.

The secondary shaft (the gear set on the right in your top pic and bottom shaft in my pic) is actually 2 concentric shafts. 1 is the secondary gear set and the other is the pinion shaft for the front differential and they spin independently of each other.

The secondary gear set is the larger set of splines that mates to the case of the center diff (transfer case, whatever). The pinion shaft connects to the viscous coupler. The viscous coupler requires a considerable amount of torque to spin so I'm wondering if this is where the confusion is coming from. The transfer shaft is the one that is connected directly to the side gear.

I found some pics of someone who has taken the center diff apart:

The diff apart:

Inside, you can see the spider gears as they mount into the diff carrier and the side gear for the rear output shaft.

The viscous coupler:

I don't know what else to say other than we could be looking at different versions of the trans and they made a major change since 1997.

Edit: I found this too: