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4WD and AWD systems explained

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Comments

  • paisanpaisan Member Posts: 21,181
    Obviously you know nothing of the STi's AWD technology it's a 6MT w/DCCD.

    Driver would determine who is faster in both Rally and Track events.

    I've ran around guys in EVOs with my 1994 Subaru Legacy Turbo on track, because I'm a better driver.

    I've had guys in Civics with 90hp kick my butt because they were better drivers than I.

    Can we all agree to disagree on this? A lot of people here are merely bench-racing which is better, and we all know that in actual use what may appear better on paper will not necessarily be better in real-life situations.

    -mike
  • chelentanochelentano Member Posts: 634
    >> Well, yes if you talk to the right people to find out the "real" story. :shades OR, you can't admit someone might know something you don't

    Yea, "talk to right people", and the you "MIGHT" find out the real story!
    "I guess you can't handle being wrong" imageimageimage
  • dcm61dcm61 Member Posts: 1,567
    The existence of “fuse” interface is not a prove, it’s your wishful thinking. They might just left it for future development.

    Huh? You put the fuse in and it disengages the transfer clutch, which eliminates all power to the rear axle (i.e. 100% of the power goes to the front axle).
  • chelentanochelentano Member Posts: 634
    >> Obviously you know nothing of the STi's AWD technology it's a 6MT w/DCCD.

    Whatever DCCD means it's still about 20 years old and EVO's SST is brand new.

    .

    >> Driver would determine who is faster in both Rally and Track events.

    Sure, driver is important but so is technology. Mitsu Pajero consistently wins Dakar Rally 12 times, 7 years in a row with all kinds of drivers.

    Speaking of EVO, the BBC armature driver keeps up well the Evo 8 MR FQ400 with professional racer on Lamborghini:
    http://youtube.com/watch?v=9y6lIaGZA4w

    This is amazing car. It produces 406 hp, from its only 2.0 L turbo engine, not to mention 1.0g handling. At 203 hp per litre, it has one of the highest specific output per liter of any roadcar engine. With a weight of around 3200 lb, it achieves a 0-60 mi/h in 3.5 seconds, better then The $600,000 Porsche Carrera GT - 3.9 seconds, or BMW M3 - 5.3 seconds.
    The BBC TopGear Power Laps rating has it on 25th spot ahead of Lamborghini, Porche, Lotus, BMW, Viper and MB. The STI is on the 54th place still very good result ahead of some Porches, BMW, Audi, Aston Martin:
    http://www.bbc.co.uk/topgear/show/powerlaps.shtml

    Also Edmunds.com road test where STI came third and the EVO X MR equipped with new Twin Clutch SST came first: http://www.youtube.com/watch?v=Gn0UkrPvPmc
  • paisanpaisan Member Posts: 21,181
    DCCD is only about 5 years old.

    DSG is not brand new, MB and BMW have had em for at least 10 years, even a low end VW has a DSG. Haaaaa.

    Anyway, let's just let it drop cause these are all very good AWD systems, both the Mitsu and the Subie. We are splicing hairs arguing over them, not to mention wasting time and space on here....

    -mike
  • chelentanochelentano Member Posts: 634
    >> DCCD is only about 5 years old.

    Actually the DCCD is at least 16 years old:
    http://en.wikipedia.org/wiki/Subaru_Impreza_WRX_STI
    .

    >> Anyway, let's just let it drop cause these are all very good AWD systems, both the Mitsu and the Subie. We are splicing hairs arguing over them, not to mention wasting time and space on here....

    Agreed. The Tidester was the one, who got this thing going again :--)
  • paisanpaisan Member Posts: 21,181
    I'm done with these bench racing discussions. GET OUT THERE AND DRIVE EM! Then come back and speak of how goo dor bad these systems are...

    I'm done.

    -mike
  • tidestertidester Member Posts: 10,059
    The Tidester was the one, who got this thing going again

    Oh, sure, blame it on ME! And you can pin rising gas prices on me too while you're at it! :P :P

    tidester, host
    SUVs and Smart Shopper
  • ateixeiraateixeira Member Posts: 72,587
    It will NEVER be 0/100 or 100/0

    What's that saying, never say never?

    The FWD mode is 100% FWD so we know it's possible.

    The existence of “fuse” interface is not a prove, it’s your wishful thinking. They might just left it for future development.

    It's also documented in the owner's manual.
  • ateixeiraateixeira Member Posts: 72,587
    Mitsu Pajero consistently wins Dakar Rally 12 times, 7 years in a row with all kinds of drivers.

    That's great ... for Pajero owners.

    Mitsubishi probably won by using the entire safety recall budget for racing instead.

    When you don't have to fix safety recalls for 24 years (1977 to 2004) that leaves a LOT of money left over for your racing program. :P

    I'm sure the racing Pajeros cost them MILLIONS, which they had due to neglecting their street cars and the safety of their customers.

    :D
  • steverstever Guest Posts: 52,454
    If you can't explain how a 4WD or AWD system works, go over to Off Topic Chatter and play in that sand box for a while.

    thanks!
  • ateixeiraateixeira Member Posts: 72,587
    Sorry, Steve.

    When I take delivery, I'll put mine up on jack stands and test out the FWD mode.

    Since it also turns off VDC, it should be very simple:

    * if only the front axle spins, it's 100% FWD
    * if both axles spin, the FWD mode does not work

    Anyone want to bet on the result?

    It will be very easy to prove that all those sources are indeed wrong. I'll be happy to prove it.
  • kurtamaxxxguykurtamaxxxguy Member Posts: 1,798
    One thing I'd enjoy reading here is info as to how responsive these AWD systems are.
    How long do they really take to detect wheel spin? Or to transfer power where needed?

    Also, othe than the center transfer clutches, what mechanisms do they use to pro-actively transfer or manage power to all 4 wheels? Do they rely on the wheel brakes? Extra clutches in the differentials or on the Axle shafts?

    Examples:
    VW commented once that their Haldex AWD systems respond within 1/4 of a wheel turn. Does that mean their systems, if faced with wheels on ice or in air, will transfer power almost instantly from those wheels?

    The '09 Subaru Forester videos clearly show some of the Foresters taking many seconds for their system to lock the spinning wheels and transfer power. That's not exactly a reactive, let alone pro-active system. Were those Subarus test mules, or the same as what we Customers buy / bought?
  • ateixeiraateixeira Member Posts: 72,587
    The brochure says "Sensors monitor parameters such as wheel slippage, throttle position and braking, to help determine torque distribution and direct it to the wheels with optimum traction."

    That's marketing-speak, but translated it means they claim the driver can influence the distribution with the throttle and brake pedals.

    The video you refer to was the one on that island, correct? Where the press drove the new 09s?

    Do you have jack stands?

    If you have the time, jack up the front of the car and put both sides on jack stands at the jack point recommended in the owner's manual.

    Then use the rear differential to jack up the rear axle. If you have 4 jack stands it's better and safer, but you don't need to get under the vehicle for this.

    Then, quite simply, test it out.

    This is a simple way to test all the theory. Like paisan said this is all bench racing until we put it to the test.

    If the front wheels spin first, that means the rear axle is not getting enough power by default to turn them. It shouldn't take much to spin wheels that are in the air - the only resistance is the weight of the wheels themselves.

    If all 4 wheels spin, the AWD is defaulting to a mode that indeed sends power to both axles. This is what I predict will happen initially.

    After that, who knows what will happen, the AWD and VDC systems will try and fail to get traction since none of the wheels have any. I predict they will cycle, one or two at a time, searching for traction that isn't there.

    This method cannot test if enough power is sent to move the vehicle, but it can determine if some power is being sent to each individual wheel.

    If you do it, please video tape it.
  • steverstever Guest Posts: 52,454
    That wasn't a reply just to you Juice - the new post title was intended to apply across the board.

    just saying... :shades:

    Wwest does a trick with jack stands and 2x4s but I'm not sure the rest of us want to go there.
  • ateixeiraateixeira Member Posts: 72,587
    I thought about that, too, but I don't think it would be safe for an amateur at home to do it alone.

    Getting 4 wheels in the air is fairly easy, though. The only tricky part is getting the jack under the 2nd axle once the first one is lifted.

    If you've ever cross-rotated your tires, you've probably already figured that out.

    I have a few Jeep buddies and will ask if they know if there's one of those ramps around here.
  • ateixeiraateixeira Member Posts: 72,587
    I actually did this test on my Miata, to see if the Diff was still working (I bought it used, so I wanted to see if it was, well, abused).

    Mine has a viscous coupling limited-slip differential on the rear axle. It's not front-to-rear, but rather side-to-side and on the rear axle only.

    All I had to do was jack up the rear axle (after blocking the front tires).

    Any how, the two sides are linked mechanically. So you can test them with the engine off.

    With an open diff, you turn one tire in either direction, and the other tire will turn in the opposite direction. This way the average speed for the axle remains zero, and the diff absorbs the difference in speed from side to side.

    With a viscous LSD, the tires should turn in the same direction.

    So I tried this. By hand, I spun the tire forward, and sure enough, the other side spun in the same direction.

    Woo-hoo! I was excited because that meant my viscous LSD was working! :shades:

    It's pretty neat, actually, you feel it engage. You need to increase the force after the weight of the 2nd tire is added to your work. I don't recall exactly, but it did not take even half a rotation of the tire, in fact it was very nearly immediate, maybe less than 1/10th of a turn of the tire.

    Heck, I'd do it again, just for the fun of it, and to see if the diff is still working, 8 years after I bought the car. I'll try to video tape it. :shades:

    The manual transmission Forester uses a viscous coupling acting as a center diff, so it works exactly the same way. If the rear axle is spinning faster than the front axle, they would lock together in the same way.

    It may be harder to test because with the vehicle off, both axles have open diffs (VDC is inactive). You might need to manually push both tires on one axle in the same direction to test if the center viscous coupling engages the front axle and makes it spin in the same direction, sort of like the Miata, only rear-to-front.

    You would still need all 4 tires off the ground, though, but in theory you could test the center viscous coupling with the engine off.

    To test an automatic Forester you would definitely need the engine on. I don't think the hand-spin test would work in this case.
  • steverstever Guest Posts: 52,454
    If you've ever cross-rotated your tires, you've probably already figured that out.

    I rotate front to back - just jacking up one side is nerve racking enough. :P

    We could all descend on a Land Rover dealer lot that has one of those little demo areas. They usually have a steep dirt ramp to play with.
  • ateixeiraateixeira Member Posts: 72,587
    Yeah, but I doubt they would want to acknowledge that anything cheaper than what they sell can get the job done. ;)
  • paisanpaisan Member Posts: 21,181
    The '09 Subaru Forester videos clearly show some of the Foresters taking many seconds for their system to lock the spinning wheels and transfer power. That's not exactly a reactive, let alone pro-active system.

    I think we are getting confused here between L/R and F/R movement of power. If you see a spinning wheel and then it shifts the power from that wheel, it could be shifting it L/R which is slower to react than F/R. The F/R transfer is a lot smoother and more fluid than the L/R movement of the power.

    A true LSD will be more fluid in transitioning power from L/R, however it still won't transfer 100% of power left and right and in addition as the LSD (either mechanical clutches or the viscous fluid in the Viscous LSDs) wear down over time the percent of power that is actually transferred L/R diminishes and the reaction time increases. Take for instance a Subaru with 100k miles on a Viscous rear LSD, the reaction time and % of Limiting of the slip will be approaching that of an open diffy. Same goes for a mechanical LSD that employs clutches in the diffy.

    The ABLS (Anti-lock Brake Limited Slip) found in the VDC and other "traction control" systems do not loose any of their reaction time or capabilities over time, perhaps your brake pads will wear out slightly quicker but they are a $50 item to replace. Rebuilding a the Mechnical LSD is about $300ish maybe more and a Viscous LSD requires an entire Diffy swap out.

    -mike
  • ateixeiraateixeira Member Posts: 72,587
    I'm curious to see that video Kurt's talking about again. Kurt - can you share a link and the time (minutes:seconds) when you observe that?

    On a few they stop intentionally to open the doors, to demonstrate chassis rigidity. I'm wondering if that pause is due to the driver.

    This hill climb is pretty amazing, note the angle of incline (37.5 degrees) and that there is no wheelspin whatsoever:

    http://www.youtube.com/watch?v=feFRI9juwV4

    The hill climb occurs at 3:00, though there are two instances.

    If the Forester were nearly FWD, as some have alleged, the front wheels would spin and only then would the rears bite down and climb. At that angle, all the weight has shifted to the rear axle, so the front axle has very little traction and there's no way it could pull the car up.

    Here's a funny (and very unscientific) comparison of the Forester and Outlander. They have a tug-of-war and the Forester wins, FWIW:

    http://www.youtube.com/watch?v=HdXjw5hACVI&feature=related

    The tug-of-war happens at 6:48.
  • ateixeiraateixeira Member Posts: 72,587
    I'd like to observe the behavior of both of these in the various modes with all 4 wheels up in the air.

    We could test and verify several things on the Outlander:

    * FWD only mode - the rear axle should not spin at all if it truly disengages
    * 4WD lock - both axles should spin at the same speed
    * Auto mode - does the front axle spin faster? Does the rear begin right away, or react only after the front axle spins?
    * Stability/Traction control - we could repeat all 3 tests with this On and Off

    For the Forester, we'd have 3 scenarios to test:

    * FWD mode with VDC off - again, is the rear axle totally disengaged?
    * AWD, VDC on - any side to side variance?
    * AWD, VDC off - reactive, proactive, same axle speeds, or what?

    The interesting part would be to observe the differences specifically.
  • kdshapirokdshapiro Member Posts: 5,751
    Here's a funny (and very unscientific) comparison of the Forester and Outlander. They have a tug-of-war and the Forester wins, FWIW

    Hey, wait a second, this is just as scientific as other videos that have been posted. Maybe even moreso. Furthermore, it's manufacturer neutral. I just think the judge, let this video be entered into evidence in the case Outlander vs Forester.
  • ateixeiraateixeira Member Posts: 72,587
    :D

    Let's get 'em both up on jack stands. I'm curious to see how both rear axles behave, especially Auto mode for the Outlander. And to see if Lock is any different.
  • psychogunpsychogun Member Posts: 129
    Mitsubishi probably won by using the entire safety recall budget for racing instead.

    When you don't have to fix safety recalls for 24 years (1977 to 2004) that leaves a LOT of money left over for your racing program.

    I'm sure the racing Pajeros cost them MILLIONS, which they had due to neglecting their street cars and the safety of their customers.


    Honestly, when you post statements like that, you are inviting flaming (baiting people). Smiley faces or not.

    To balance out your post, you could have mentioned that Subaru was also guilty of hiding defects and was forced to recall 2 million cars in 1997.

    Fair play.
  • kdshapirokdshapiro Member Posts: 5,751
    To balance out your post, you could have mentioned that Subaru was also guilty of hiding defects and was forced to recall 2 million cars in 1997

    To be fair, they weren't guilty of it for 24 years.
  • paisanpaisan Member Posts: 21,181
    Let's get 'em both up on jack stands. I'm curious to see how both rear axles behave, especially Auto mode for the Outlander. And to see if Lock is any different.

    The jack stand trick won't work. I'm pretty sure that the AWD system takes into account TPS, and weight shift (F/R) as well to determine where to put the power. It also learns combinations of TPS, weight shift, speed to pre-emptively move the power.

    -mike
  • psychogunpsychogun Member Posts: 129
    Yes, Subaru was guilty for only 7 years. Mitsubishi was guilty for 30 years.
    I'm not here to blindly defend any manufacturer.
    In my humble opinion, you can be guilty of hiding defects for just a month, you're still guilty of a serious lapse in judgment and ethics.
    Regardless, both companies are past this. Both have new, more transparent management structures in place.
    I find it unproductive to rehash the past. Especially considering that this is 2 full model generations behind us.
  • kdshapirokdshapiro Member Posts: 5,751
    .. find it unproductive to rehash the past. Especially considering that this is 2 full model generations behind us.

    Only in the sense, for me, I don't and won't trust Mitsubishi cars. Maybe they've changed, but I vote with my dollars.
  • psychogunpsychogun Member Posts: 129
    I'm, by no means, trying to change how you feel about Mitsubishi.
    You obviously have your valid reasons.
    Conversely, I feel I have my valid reasons to believe that Mitsubishi makes great cars. One of many reasons being, we have owned 4 different models in several countries over the past 25 years (one of them for 7 years).
    Again, that's just my experience.
  • kdshapirokdshapiro Member Posts: 5,751
    I agree one needs to be comfortable with these large $$$ expenditures.
  • ateixeiraateixeira Member Posts: 72,587
    Absolutely true, and notice that ended right around the time their winning streak in WRC ended (3 in a row from 1993-1995).

    Point is, racing success is mostly a marketing thing, and has very little to do with how good (or bad) a manufacturer is doing making production cars.

    My original point remains, and is actually reinforced by Subaru's smaller yet still significant troubles.

    WRC championships were great PR for Subaru, but the fact is Prodrive now owns Aston Martin, and the Subaru-based Prodrive P2 never went into production. Multi-million dollar race cars/trucks have very little in common with what you'll find for sale at the dealer.

    Same for Mitsubishi and its Dakar racing program - not very relevant to production cars, especially models besides the Pajero.

    When it comes to addressing issues that do come up, most Subaru owners are satisfied with how their dealers do repairs (better than the industry average today). So they have earned their customers' trust back.

    For Mitsubishi, they're not there yet. Only 44% of customers are satisfied with the service they get from their dealers, 2nd last in the industry (only VW is worse).

    So IMHO Subaru has made the turnaround, while Mitsubishi is still working on it. At least their products are much better - now it's time to work on customer service.

    To bring this back on topic, if our ramp tests cause damage to either or both of the AWD systems, at least I'd be more likely to be satisfied with the repair.
  • ateixeiraateixeira Member Posts: 72,587
    Good point, paisan, but let's think about this.

    The automatic Forester's system, specifically, supposedly uses as input the following:

    * wheel slippage
    * throttle position
    * braking

    That's from the 2009 brochure.

    They don't mention TPMS. Not sure about weight shift - but they could determine that from the throttle (shifts weight back) and braking (shifts weight forward), so your point is certainly valid. If you disable the traction/stability control it may eliminate the wheel slippage input, then again maybe not - the data is still gathered, it depends on which systems could still use that data.

    So in the jack stand test, the throttle position could be controlled if a 2nd person is sitting in the car. Same with the brakes. Wheel slippage would be fine as that is sort of the point of the whole test - to observe what occurs when the wheels are allowed to slip.

    I think we could still see if by default both axles get power, if one spins faster than the other, if both sides spin, etc. Not as good as a dynamic test, like the ramp, but more of a static test with small/no load.

    The Tribeca's AWD system goes a few steps further and uses inputs from the steering angle sensor, yaw velocity, acceleration sensors, and braking force (I think they mean pedal pressure, to measure the driver's intention). So in that case you really would need a ramp for a dynamic test.

    Thing is, I've already seen a Tribeca succeed at that. A Legacy GT as well.

    So now I want to see a Forester try it.
  • paisanpaisan Member Posts: 21,181
    Also, one should never put a car in gear on jack stands. It is very dangeros.

    -mike
  • dslgdslg Member Posts: 3
    I am buying a 2008 CR-V and live in the south so there isn't any snow. So should I consider the 4WD because of slick roads when it rains or just save my money and go with 2WD?
  • paisanpaisan Member Posts: 21,181
    AWD will help you in not only slick wet roads, it will also be helpful if you drive on any roads that accumulate dirt/debris/sand/etc on the edges. These areas can be very slippery and the AWD can help in keeping you from losing control of your car.

    -mike
  • ateixeiraateixeira Member Posts: 72,587
    Do you find yourself driving on gravel, sand, or unpaved roads? It would come in handy in those situations.

    If not, though, then I would pass. RT4WD is an on-demand part-time system and you might find it would rarely (if ever) engage. If you don't slip, it's always FWD anyway.

    FWD will cost less up front, the vehicle weighs a bit less, and it should be slightly more fuel efficient.
  • erfansaberierfansaberi Member Posts: 1
    hi, i have a envoy slt 2003. recently i got a problem with engine rpm. rpm jumps up from 700 to 900 and then after a few miles driving comes down and then again after miles driving goes up. it is making me mad and i feel damaging clutch and brake too while i am staying in traffic. please help me to find out the reason. thanks.
  • ajaksajaks Member Posts: 11
    Can I remove the front driveshaft on my NP 233 and drive it 2WD? I mean will this work or cause problems?
  • heyboerheyboer Member Posts: 6
    Hello. Looking at a 2006 Buick Rainier(AWD) or a Pathfinder (4WD) to pull a boat. I've heard you can really get nailed with tire problems on an AWD. True? Any other input on the two vehicks is appreciated. No off-roading will be done. Probably could get by with 2wd, but due to snow and the occasional tough ramp I might as well go with 4. The pathfinder has a switch to select the drive. No switch on the Buick. Thanks.
  • paisanpaisan Member Posts: 21,181
    AWD doesn't burn up tires any faster, but you need to rotate them ever 5k to make sure they wear evenly because it can cause problems for the AWD system if they are severly worn more in the front or back.

    I would go for the Pathfinder, great vehicles.

    -mike
  • rshollandrsholland Member Posts: 19,788
    I agree with Mike. It's no contest. Take the Pathfinder. Besides, you can probably get a great deal on a new one these days, as everyone is shunning "true" SUVs because of the fuel prices.

    Bob
  • paisanpaisan Member Posts: 21,181
    The pathy also has a backup camera pretty much std on all of them, great for backing up ramps.

    -mike
  • rshollandrsholland Member Posts: 19,788
    The only problem I have with the Pathfinder is that the 3rd row seat is strictly for kids. The Explorer, Pilot, CX9 all have better 3rd-row seats than the Pathfinder.

    But if that's not an issue, I say go for it.

    Bob
  • heyboerheyboer Member Posts: 6
    Thanks guys. Almost pulled the trigger on a 2005 Patfinder over the weekend. Geat deal, but no curtain airbags. Still might do it, but now looking at Toyota 4 runners also. Almost impossible to find one in Chicago with side/curtain airbags. Considering Merc Mountainier also because of the airbags. Any input on these vehicals? Reliability of the Merc?
  • paisanpaisan Member Posts: 21,181
    We drive the V8 Explorers at work, late models (last gen and present gen) and they are horribly unreliable. Haven't left us stranded but, little things seem to break on them a lot.

    -mike
  • heyboerheyboer Member Posts: 6
    Thanks. Actually I ended up with a 2004 4Runner Limited V8. I did some reading and decided the side and curtain air bags were a must. Not many have them. Test drove one at Carmax. Loved it. Bought it for 177w/ brand spanking new tires at a Benz dealer. Tough for a native Detroiter to say, but it is a sweet ride.
  • paisanpaisan Member Posts: 21,181
    Good to hear you didn't buy the explorer/mountaineer.

    Toyota makes a good vehicle, so I'm sure it will serve you well.

    -mike
  • aagicaagic Member Posts: 1
    Hi guys, I'm new here and could use a little help. I do some light off-roading, mostly on the beach which can be a bit tricky if the vehicle is not somewhat capable. I currently drive a 4x4 Jeep Commander and I drove a Cherokee Sport before that. My lease is up soon and I'd like to get another SUV which will allow me to go on the beach but I'd also like to improve my gas mileage. The problem is that virtually all of the 2008s I see with good gas mileage are AWD instead of 4x4 and I'm not confident in their ability to get me out of the sand. I could use some advice. Are the AWDs capable enough? What are the true 4x4s out there for 2008 with decent gas mileage? Right now I'm looking at the Patriot which gets 20/22 MPG with the off road package. Thanks for your help. - AAGIC
  • paisanpaisan Member Posts: 21,181
    Key is to air-down your tires.

    I'm not a big fan of a FWD-based offroad vehicle like the patriot.

    I'd look more toward the Nitro/Liberty if you plan on doing offroading with it.

    -mike
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