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4WD and AWD systems explained

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Comments

  • kdshapirokdshapiro Posts: 5,751
    Similiar to the way websites report performance results.
  • chelentanochelentano Posts: 634
    Great. That only proves what I have always said: 4EAT Subaru is practically a FWD car by default or part-time AWD, whichever way you like.
  • chelentanochelentano Posts: 634
    >> An aside, my guess is that wiki, NYT, and the other "credible" sources

    How about Edmunds.com? You work for the company, it not it credible enough?
    .

    >> my guess is that wiki, NYT, and the other "credible" sources all are feeding off each other to get their facts.

    All these sources are actually feeding from Subaru: Subaru used to report the same 90/10-50/50 numbers every year untill 2004. They stopped from 2005.
  • kdshapirokdshapiro Posts: 5,751
    No matter what you call the Foresters' drive train, it can power up a ramp with any one wheel without flipping any switches or having excess tire wear. I'd like to see the Outlander power up a ramp with any one wheel as the Forester does.(and it may, I don't know).
  • chelentanochelentano Posts: 634
    >> No need to rely on my knowledge, just check out the video.

    What video? The one made at Subaru dealership? A subaru salesman is the last person I’d trust. Can you offer an independent video/commentary?
    .

    >> I'm guessing the 2009 Forester will be able to accomplish the same thing. Have you looked at the video.

    That's just a guess.
  • kdshapirokdshapiro Posts: 5,751
    That post was from mid-2002. Contained a lot of interesting and detailed information about Subaru AWD systems.

    The biggest issue for these systems as I can tell, is when only one wheel from each axle has traction. I'm guessing the 2009 Forester will not have a problem with that scenario, based on the previous video, but earlier models will just spin their wheels.
  • kdshapirokdshapiro Posts: 5,751
    What video? The one made at Subaru dealership? A subaru salesman is the last person I’d trust. Can you offer an independent video/commentary?

    Okay, you don't have to trust the video, but I believe it to be representative of what is being shown, since I've seen other videos.
  • chelentanochelentano Posts: 634
    >> No matter what you call the Foresters' drive train, it can power up a ramp with any one wheel without flipping any switches or having excess tire wear.

    May be Forester can power up a ramp in subaru paid video at subaru dealership, but otherwise it's seems to be tough in a real life conditions. I wonder why:

    http://www.youtube.com/watch?v=-tMgWtlxeb8&NR=1
    http://youtube.com/watch?v=g6H3IOtE6Q8
    http://www.youtube.com/watch?v=guTQWkpPFa4
  • kdshapirokdshapiro Posts: 5,751
    Maybe, but at least it doesn't get stuck in the mud, or spin it's wheels more then the Forester.

    And, if the Subie AWD is part-time as you claim, then the Outlander AWD is certainly part-time as well.

    Actually, according to your definition, FWD mode, split ratio, etc, there aren't any real AWD cars on the road in this price range.
  • kurtamaxxxguykurtamaxxxguy Posts: 1,751
    Some of those videos above showed the achilles heel of many AWD systems: side-side transfer. Foresters without the LSD or VTC would be in trouble if one side was on ice, other side with traction.
    If all 4 wheels are on ice or banana-peel surface, __no__ AWD system is going to be of much help.
  • wwestwwest Posts: 10,706
    Sorry, I discarded the Subaru AWD system as non-viable long ago.

    But the insofar as I know any Toyota/Lexus "AWD" model with a sideways mounted engine is just as non-viable.

    The only "viable" AWD model that I am aware of with a sideways mounted engine is the Acura RDX with SH-AWD. My daily driver happens to be a mostly non-viable '01 AWD RX300 since I don't need AWD "viability" all that often. I have a '94 AWD Ford Aerostar for those times, and the RX has special modifications allowing me to use REAR tire chains for the few times I get caught out in adverse conditions.
  • wwestwwest Posts: 10,706
    AWD Vehicles with sideways mounted engines or derived from a FWD "base" almost all have front drive torque biasing, often as high as 100/0 but usually at least 90/10 absent TC intervention. So when wheelspin/slip develops due to engine torque and/or low roadbed surface traction it is almost always at the front wheels.

    Because those are the same wheels you use for directional control of the vehicle once wheelspin/slip develops regaining roadbed traction is of the ULTIMATE importance. So, TC will activate virtually INSTANTANEOUSLY when wheelspin/slip develops on one of these vehicles.

    TC, to prevent the potential for EXTREME torque stear, will quickly activate braking of BOTH front wheels simultaneously. Since this is an issue of ULTIMATE importance TC will also INSTANTLY dethrottle the engine, not giving the driver even a millisecond to react and lift the gas pedal, unlike TC on many RWD vehicles which often allow 100's of milliseconds for the driver to react and "feather" the throttle.

    To that end Toyota has just announced a new feature for RWD and R/AWD vehicles, a TC "sub-mode". Once the driver activates the sub-mode TC feature a limited level, period, of engine torque driven rear wheelspin/slip will be allowed without TC automatically activating.

    Subaru: Symmetrical AWD....

    Idiots.
  • kdshapirokdshapiro Posts: 5,751
    For those of us who don't need chains or want an Acura, the Subaru Symmetrical AWD is better than SH-AWD. From friends who have SH-AWD it's a performance enhancement and dubious one at that. An Acura is non-viable.
  • wwestwwest Posts: 10,706
    I'm puzzled...!!

    All three of those YouTube videos show, indicate, that the Subaru AWD system performed very well, even SUPER well IMMHO. The only thing that was lacking would be more traction between the tire tread and the "road" surface. IMMHO even a 4X4 with locked center and rear diff'ls would have needed tire chains, or heavily "lugged" wheels, in the examples shown.
  • kurtamaxxxguykurtamaxxxguy Posts: 1,751
    One drawback I see wrt the Subaru systems is they do not appear to be as proactive as one might think.

    The rough road test Subaru devised (and claimed only their vehicles could traverse (not true, I suspect - the vids showed only the CRV getting stuck ) ) showed the '09 Forester clearly spinning wheels and taking several seconds trying to figure out whether or not to brake the spinning wheels.
    So in that case, the Subaru system is not "pro-active".

    It would be useful to know just how fast the Subaru VDC responds to momentary loss of wheel traction/skidding in normal driving. That's all the '09 Forester has (aside from front/back transfer clutch control ) to manage torque and wheel slip.
    There are no LSD's at either end of the vehicle.

    The STI, by comparison, does have a Torson LSD in the rear and a Bevel LSD up front.

    Meanwhile, other videos of the Land Rover LR2 showed this vehicle on a similar road, and its unloaded, in-air wheels did not pick up speed or spin wildly. That vehicle, per other videos and close reading of specs, apparently has a "pro-active" system.
  • kdshapirokdshapiro Posts: 5,751
    The STI, by comparison, does have a Torson LSD in the rear and a Bevel LSD up front.

    These are not sophisticated 4wd systems. I owned a Jeep with the top end 4wd system, which delivered almost 100% torque to any one wheel. I had plenty of opportunity to test it in deep snow for the years I owned it. You could tell, barely, when torque was transferred to the front wheels and then passed around as wheels slipped. This happened almost instantly.

    These AWD systems are meant to keep the vehicle from getting stuck. The torture tests shows the limitations at the extreme, but it does show the vehicle will or will not get stuck. The LR has the hardware for real offroading, but it isn't very nimble. My old Jeep would not spin any wheel off the ground more than 1/2 turn.
  • ateixeiraateixeira Posts: 72,587
    chelentano wrote:

    So I offered total 6 credible sources, covering 2000 models of 4EAT Forester and Outback (read previous posts), incl. Wikipedia, NYTimes, Car and Driver, Popular Mechanics and Edmunds.com. They all say that split was 90/10 to 50/50

    And those sources are all wrong.

    See the pic below as proof - it shows the FWD fuse, labeled clear as day. The fuse box even includes a spare fuse and a tool to use to insert them, so you don't need to buy anything.

    The Outlander has the switch on the center console. Subaru's is less convenient - it's in the fuse box. Both have the same effect, though - the rear axle is disengaged completely.

    When the Subaru goes in this 100% FWD mode, i.e. power split 100/0, it will light up a light in the dash "AWD", indicating the system is disengaged. Here is a pic of that light, from cars101:

    image

    chelentano himself said that because the Outlander had a FWD mode, that was proof it could go 100/0, completely FWD.

    For the same exact reason, the Forester can, too.

    All of those sources are wrong. End of story.
  • ateixeiraateixeira Posts: 72,587
    May be Forester can power up a ramp in subaru paid video at subaru dealership, but otherwise it's seems to be tough in a real life conditions. I wonder why

    Ground clearance, first and foremost. The original Forester only had 7.5".

    The new XT has 8.9", more than the Outlander, FWIW.

    The 2nd reason would be the overhangs.

    Again, that was a weak spot on the early Foresters, but that has been addressed. The 2009 Forester has an approach angle of 24.8 degrees.

    That beats the Outlander's 21 degrees.

    The Forester's departure angle is also 24.8 degrees. This is smart design. If you can get the front bumper past without scraping, you can get the rear bumper past without getting caught up. Very smart.

    The Outlander's departure angle is only 18 degrees (source: Car & Driver). That presents the same problem early Forester's had - the long rear overhang can get caught up on obstacles.

    This is poor design. You may get the front bumper past (21 degree angle) but not the rear (only 18 degrees).

    That answer your question, I believe. :P
  • chelentanochelentano Posts: 634
    >> The new XT has 8.9", more than the Outlander, FWIW.

    How much more? 0.4” – it’s a marginal difference.
    .

    >> The 2009 Forester has an approach angle of 24.8 degrees. That beats the Outlander's 21 degrees.

    Your degrees and fractions of inch would not help in these situations. The Subaru overrated AWD system just can’t get it up. I can use your quote: "this is poor design":

    http://www.youtube.com/watch?v=-tMgWtlxeb8&NR=1
    http://youtube.com/watch?v=g6H3IOtE6Q8
    http://www.youtube.com/watch?v=guTQWkpPFa4

    The Outlander on the other hand has plenty of "degrees" and ground clearance to do this:

    http://www.youtube.com/watch?v=k3arUMr2PsI
    http://www.youtube.com/watch?v=7RUrT_0tvn8&feature=related
    http://www.youtube.com/watch?v=W0kdzSklDWE&feature=related
    http://s215240594.onlinehome.us/dakar08.jpg
  • chelentanochelentano Posts: 634
    >> See the pic below as proof - it shows the FWD fuse, labeled clear as day. The fuse box even includes a spare fuse and a tool to use to insert them, so you don't need to buy anything.

    Wow! Fuse insertion - what a high tech way to control Subaru AWD! Fuses, 20-year old awd systems, 40-year old transmissions, and finally first diesel engine in 2008: all the exciting technology coming from Subaru!

    The fuse only proves what I have always said: 4EAT Subaru is practically a FWD car by default or part-time AWD, whichever way you like.
  • kdshapirokdshapiro Posts: 5,751
    The fuse only proves what I have always said: 4EAT Subaru is practically a FWD car by default or part-time AWD, whichever way you like

    Then the Outlander is the same, you pick it. As an aside if you pit and Outlander of the same year with the Forester, I don't think the Outlander would have been able to move.
  • dcm61dcm61 Posts: 1,480
    4EAT Subaru is practically a FWD car by default or part-time AWD, whichever way you like.

    90/10 vs. 85/15 - it's a marginal difference.
  • chelentanochelentano Posts: 634
    >> 90/10 vs. 85/15 - it's a marginal difference.

    85/15 is in Auto mode. But Outlander also has a true full-time 4WD Lock mode, which by default delivers more than twice of the rear torque vs. Forester. The

    Forester has only one part-time on-demand mode. That's why this practically FWD vehicle can't get up to hill on these videos.
  • chelentanochelentano Posts: 634
    >> Then the Outlander is the same, you pick it.

    Nope. The Outlander also has a true full-time 4WD Lock mode, which by default delivers more than twice of the rear torque vs. Forester.
    .

    >> if you pit and Outlander of the same year with the Forester, I don't think the Outlander would have been able to move.

    You "don't think"? It's only a wishfull thinking. The Forester's AWD system is about 20 years old, so the current Forester is not any better. The 4-speed auto transmission is another subaru antique technology invented by Romans. But forget that lousy 6-8 speed and Twin Clutch transmissions, Subaru is working hard on CVT now!
  • kdshapirokdshapiro Posts: 5,751
    You "don't think"? It's only a wishfull thinking

    Okay, let me rephrase that: "I know". How do I know, because the reviews of a previous generation Forester against an Outlander said the Outlander kept spinning it's wheels while the Forester didn't.

    The Forester's AWD system is about 20 years old, so the current Forester is not any better. The 4-speed auto transmission is another subaru antique technology invented by Romans. But forget that lousy 6-8 speed and Twin Clutch transmissions, Subaru is working hard on CVT now!

    The antiquated Forester XT will absolutely dust the Outlander. All the gears in the world won't help the Outlander.

    Nope. The Outlander also has a true full-time 4WD Lock mode, which by default delivers more than twice of the rear torque vs. Forester.

    Nope, the Forester has the same system as the Outback, which has been shown in torture tests to climb up "rollers" with one wheel. So while there isn't a video of a 2009 Forester doing the same thing, we'll have to wait. The advanced Subaru AWD doesn't need a lock mode to compensate for an otherwise mediocre AWD system as in the Outlander with multiple dubious modes of operation.
  • steverstever Viva Las CrucesPosts: 41,881
    subaru antique technology

    The CVT will be an oldie but goodie too, seeing as how Leonardo da Vinci invented it about 500 years ago. (link)

    Shall we get back to the topic, which is how explaining how they work?

    Moderator
    Minivan fan. Feel free to message or email me - stever@edmunds.com.

  • chelentanochelentano Posts: 634
    >> The CVT will be an oldie but goodie too, seeing as how Leonardo da Vinci invented it about 500 years ago.

    Great find, Steve. Leonardo da Vinci would be proud finally seeing CVT on Subaru.
  • chelentanochelentano Posts: 634
    >> Nope, the Forester has the same system as the Outback, which has been shown in torture tests to climb up "rollers" with one wheel.

    Yea, I have seen the Subaru sales videos. I also have seen how it can Subaru can "climb up" in real life conditions:
    http://www.youtube.com/watch?v=-tMgWtlxeb8&NR=1
    http://youtube.com/watch?v=g6H3IOtE6Q8
    http://www.youtube.com/watch?v=guTQWkpPFa4
  • kdshapirokdshapiro Posts: 5,751
    You keep posting videos of a circa 2003 Subaru. Do you know why there are no videos of an Outlander getting stuck. Nobody in their right mind would take a previous generation Outlander into any slick situation. It would have to be towed out.

    Try these in your Outlander:

    http://youtube.com/watch?v=gwrrbYiLcjA&feature=related
    http://youtube.com/watch?v=YonP3_c-2Nc&feature=related
    http://youtube.com/watch?v=SodoaksRJAU&feature=related
    http://youtube.com/watch?v=_ZwfRpk8XYo&feature=related

    Here's more:

    http://youtube.com/watch?v=n2b-fMQ4tdk&feature=related
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