Subaru Impreza AWD System

[Ramblejam]

I was always under the impression that Subaru AWD was intelligent and rather adept at finding traction. Take a look:

Can anyone offer some insight here?

 

[BowNisPar]

I hope that was a rental.

 

[joegreen]

Originally Posted By: BowNisPar

I hope that was a rental.

why?

 

[gathermewool]

I'll start off by pointing out the fact that both the front and rear differentials are open, meaning that effectively 100% of the torque will be transmitted to the wheel with the least amount of grip (to put it extremely simply.) I'm not sure how turning traction control off effects the electronic brake distribution of the Subaru Vehicle Dynamics Control system, but there are two big things I notice: 1. With the rear right wheel in the air, the car still moves forward, maybe because most of the torque is applied to the front wheels by default and not enough is sent to the rear, nor is it needed to support getting over the hill. 2. With the front right wheel spinning, neither does traction control appear to cut power nor does VDC appear to be braking the front right wheel. Also, it may be a Subaru, but it's an economy Subaru, and while the layout may be more conducive to better dynamics, is it really better than any other cheap AWD system out there? To know we'd have to see this same test performed on a slew of other AWD vehicles. Finally, how many FWD vehicles do you think would pass this test? That's a real question, not a sarcastic Subaru sulky response.

 

[BowNisPar]

Because I wouldn't "test" my own vehicle like that.

 

[Chris142]

Needs lockers

 

[Noobie]

It does seem that TC is working when they tried the 2nd and 3rd time but it looks like it wasnt braking the wheel enough and needed some more throttle.

 

[gathermewool]

Originally Posted By: Noobie

It does seem that TC is working when they tried the 2nd and 3rd time but it looks like it wasnt braking the wheel enough and needed some more throttle.

I really don't think TC would let the front right wheel free-spin like that, though. I don't know for sure, but I'm not certain that turning TC off fully defeats VDC, but maybe it deadens it, meaning less brake force is used, and is meant to rock your car out of a snowed-in spot, not take on a hill three-wheeled. On the other hand, he performed the same test on a CX-9 and CX-7 with similar results...

 

[oilpsi2high]

AWD is for suckers who know nothing about the physics of an automobile.

 

[BowNisPar]

Originally Posted By: oilpsi2high

AWD is for suckers who know nothing about the physics of an automobile.

Explanation please.

 

[tinmanSC]

Originally Posted By: oilpsi2high

AWD is for suckers who know nothing about the physics of an automobile.

Soo... that would be just about everyone? So you're saying that AWD is for just about everyone...? Most people don't need to know those details. They just need a vehicle that gets them from point A to point B safely with without headache. Soccer moms don't need to know torque vectoring, suspension crunch and how to do a Scandinavian flick.

 

[gathermewool]

Originally Posted By: oilpsi2high

AWD is for suckers who know nothing about the physics of an automobile.

100% wrong, since this video and how it is a display of the AWD system and not the driver's skill makes your post irrelevant. I took a winter driving course and the second worst car was the RWD Porsche with new winter tires. A professional driver spun out twice while driving cautiously and what seemed to be relatively slowly during the emergency maneuver portion of the course. The worst car? Some lady decided to come to a winter driving course in her Mazda 3 hatch with all-season tires. She had trouble making it up the hill without a massive amount of momentum. Another STI and I had the best results (similar LSD configurations all around.) I had fun achieving full boost up-hill, starting at a lower speed at the beginning of the hill. Blizzaks, LSD's with electronically locked center differential, as well as Subaru's VDC helping out with brake application resulted in amazing amounts of traction. What I thought was interesting, was that the smaller FWD cars with good snow tires were able to get around just fine, too. The AWD CUV's with snow shoes were alright, but tended to be a little more ungainly and definitely lost traction more quickly than the cars did. So, tires make a huge difference Drivers make a huge difference (you're right on that point) drive-wheel(s) scheme also plays a roll, since amazing grip to a non-driven tire won't do squat for you. Grip all around, but all power going to one wheel without grip won't do squat for you.

 

[rjundi]

Gathermewool eludes to this but Subaru actually has many variants of AWD that all have common trait of full time instead of part time. Currently they have 5-6 different systems going currently tailored to each vehicle. They have moved away from LSD mechanically to electronic versions. My guess is this base looking Impreza is auto with open diff. Interesting test. You'd see results all over the map with a fleet of 2015 Subaru's models here down to automatic vs cvt vs manual transmission model of same vehicle.

 

[horse123]

Called open diffs. Every AWD car except the more expensive ones have them. I've done plenty of climbing up snow mounds that jeeps have trouble getting on with my Impreza. from past winters

 

[6starprez]

Originally Posted By: Ramblejam

I was always under the impression that Subaru AWD was intelligent and rather adept at finding traction.

There are several videos testing Subaru AWD. Here's one:

 

[bsmithwins]

According tho this, the center differential is a limited slip, viscous coupling but the front and rear differential are not locking: http://www.awdwiki.com/en/subaru/ BSW

 

[HerrStig]

Originally Posted By: oilpsi2high

AWD is for suckers who know nothing about the physics of an automobile.

Like the military, where anything they use which isn't tracked is AWD?

 

[gathermewool]

Originally Posted By: bsmithwins

According tho this, the center differential is a limited slip, viscous coupling but the front and rear differential are not locking: http://www.awdwiki.com/en/subaru/ BSW

Not in the auto, which will electronically transfer power based on slip via clutch action. The front and rear are open, but electronic brake application attempts to stop spinning wheels and transfer power to a wheel with grip. This works a lot better with a LSD, since the torque multiplication requires much less available grip (via actual friction on the slippery surface and brake application) to provide enough torque to the opposite wheel to get forward motion.

 

[Ramblejam]

Thanks everyone, especially gathermewool, for the additional insights. Appreciate it.

Originally Posted By: gathermewool

On the other hand, he performed the same test on a CX-9 and CX-7 with similar results...

It's very interesting to me that most car-based, AWD vehicles perform about the same; start up the incline, then tires lift off at breakover, and progress stops (coupled with excessive wheelspin). With all I hear about Subaru and their supposedly superior AWD system, I just expected better spin management and ability to direct power. With that said, take a look at this. Not a direct comparison by any means, but what I expected from Subaru.

If anything, I'm truly most impressed by the Canyon. Yes, it's a truck, but there's no sophisticated electronic wizardry at play here...just an old school, dumb 4WD system underneath with nothing more managing traction than a G80 in the rear end. Spin, it clunks into place, and on you go:

 

[horse123]

^ That luxury SUV has significantly more flex/travel between the wheels than a small subaru.