Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!





4WD and AWD systems explained

1373840424348

Comments

  • ateixeiraateixeira Posts: 72,587
    Interesting, thanks.

    up to 60 percent of available torque is sent to the rear wheels

    That means the 0/100 claim made above is wrong, though.
  • ateixeiraateixeira Posts: 72,587
    Wrong for the simple reason traction control was added.

    I'm sure enhancements were made between 2003 and now by both Subaru and Mitsubishi, traction control being among those.
  • ateixeiraateixeira Posts: 72,587
    This is what happens when you let the marketing folks take control, rather than engineering. ;)

    Let's test the 90/10 limit first.

    You can insert a fuse to make the Forester purely FWD, i.e. 100/0. So right there is proof the 90/10 limitation does not exist.

    The Outlander has a FWD mode and this was used to justify how it too can go to a full 100/0 split. For the same reason, the Forester can to, it's just a fuse rather than a knob. How you turn on the FWD mode differs, but the result does not.

    So marketing is wrong about the 90/10 limit.

    Now let's look at the 50/50 theory. I think the marketing folks are misinterpreting what the engineers say about the design. There is a language barrier (because the engineers are Japanese) and a technical barrier, because the marketing folks aren't trained in mechanical engineering.

    So then, what do they mean by an even split? They could mean that the front and rear axle will turn at the same speed, but that does not mean 50% of the power will go to each axle. Where the power goes would actually depend on the traction available.

    Think about it, if both rear tires are on ice, and get no traction, even a tiny amount of power to that axle would make it spin. If there is no resistance, the power finds the path of least resistance, and the tires would spin like crazy.

    Click this link and forward to 2:48:

    http://www.youtube.com/watch?v=t09ExAUgtyE&feature=related

    On the ramp, where marketing hype doesn't matter, you can actually see the AWD send power to the rear axle. At first the front tires spin, indicating a front bias, but then power is transfered to the rear axle, enough to move it up the ramp. Note that by the end of the rollers, the front wheels have nearly stopped spinning.

    If the front wheels were still getting 50% of the power (86.5 horsepower), they would be spinning like mad. The driver is applying enough throttle for the rear axle to move the Forester up that ramp, yet the front wheels barely spin at all.

    Where is the 50% split to the front wheels? Why are they not spinning? 86.5 horsepower barely turns wheels on ice? Can't be.

    Then forward to 3:08 on the same video.

    That's when the front axle is asked to do the job by itself, while the rear axle has no traction. Notice the rear axle doesn't spin at all.

    You could argue that 10% of the available power (now only 17.3 horsepower) may indeed not be enough to make the rear axle spin, but we know that the system is capable of disengaging the rear axle entirely in FWD mode anyway.

    As for all the magazines, well, they basically collect press kits from the manufacturers and just regurgitate what the manufacturer claims in those kits. A lot of times you'll notice they even copy/paste the text, which is just lazy.

    Personally, I give more weight to the magazines that go out and test these claims, rather than the claims themselves.

    All of those magazines also said the 1997 Ford Mustang had 225hp, but Ford downrated it to 205hp when the Cobra models came out. Even the Cobras came up short.

    Yet all the press published the 225hp number, because that is what Ford told them. Everyone was wrong.

    Same for Mazda with the Miata and RX8. Again everyone was wrong.

    Thankfully we have the 4WD ramp and the dynomometer to verify the accuracy of those claims, which are often bogus.
  • kdshapirokdshapiro Posts: 5,751
    Based on the video the 2009 Forester should be able to drive the car if only one wheel has traction. Interesting. I'm sure there will be some comments about video bias, though.
  • ateixeiraateixeira Posts: 72,587
    Could be, but we really need to get a 2009 on that ramp for a re-test.

    We know the AWD system is capable of sending enough power F<>R, so that if either axle has traction it will make it up.

    Now the question is, can the traction control system shift power side to side?
  • paisanpaisan Posts: 21,181
    Now the question is, can the traction control system shift power side to side?

    That's what the VDC does. Since the VDC is similar to that on my Armada and the Frontier, I'd hazard a guess that it should be able to tote it up. Only issue might be if that 1 wheel doesn't have enough power to carry the weight of the vehicle up.

    I have climbed up slippery driveways where the rear of the A had no traction, and the front was alternating between left and right sides using the VDC. Only thing is the A has 305hp/385lbs torque.

    Would be interesting to try it out, my gut feeling is the forester 09 would do it w/o a problem.

    -mike
  • ateixeiraateixeira Posts: 72,587
    Well, now that we have one on order (ETA July 2009) when we get it I'll ask around the local 4x4 clubs if they have one of those ramps.

    If I can find one I'll invite others to come along and bring their rides.
  • dodo2dodo2 Posts: 496
    This would be very interesting. Where are you located?
  • chelentanochelentano Posts: 634
    >> Wrong for the simple reason traction control was added. I'm sure enhancements were made between 2003 and now by both Subaru and Mitsubishi, traction control being among those.

    Again, you don&#146;t follow the discussion, taking phrase out of context. Those last few posts are about the 4EAT power split of 90/10 &#150; 50/50, which has not changed since nineties, according to all the publications I have mentioned.

    Traction control does not affect Front/Rear power split ratio. In any case, traction control is not a feature of AWD but a separate system. Traction control and various forms of VSC are standard now even on non-AWD cars.

    Subaru traction control/VDC was not introduced after 2003, but it was introduced in 2001 and even mentioned on 2003 NY Times chart.
  • ateixeiraateixeira Posts: 72,587
    The correspondence from Subaru stated they were going to revise the marketing materials because the whole power split issue was being misinterpreted.

    The media got it wrong all along, that's why they changed the policy about publishing those figures in the first place.

    Traction control does not affect Front/Rear power split ratio

    Not true. In fact, Toyota uses open diffs and relies on traction control primarily to shift power. It is a reactive system, but it does work.

    Traction control systems are often integrated into AWD, in fact Toyota's depends on it entirely.

    As I'm sure you know, with 3 open diffs (center, front, rear) all the power would leak out to a single wheel it offered the least resistance, i.e. 1WD.
  • ateixeiraateixeira Posts: 72,587
    I can't believe you're still using the 2003 NY Times chart as a reference.

    Can you at least admit they were wrong about "Audi all"?

    It's hard to have an intelligent conversation about AWD if you cannot acknowledge the difference between a Torsen and a Haldex. :sick:
  • kdshapirokdshapiro Posts: 5,751
    Those last few posts are about the 4EAT power split of 90/10 &#150; 50/50

    Correction the last few posts are about the 80/20/80 split, which hasn't changed lately. Except I'm guessing in the 2009 Forester, based on the latest video, one wheel possibly could drive the car.
  • chelentanochelentano Posts: 634
    >> Correction the last few posts are about the 80/20/80 split, which hasn't changed lately.

    No evidence of that, unless you could post some credible links. Quite contrary: all sources I posted suggest 90/10 - 50/50 split since nineties.
  • chelentanochelentano Posts: 634
    >> The correspondence from Subaru stated they were going to revise the marketing materials because the whole power split issue was being misinterpreted.

    Well, untill they revise it, we not going to make stuff up and we use the available info.


    >> Traction control does not affect Front/Rear power split ratio
    >> Not true. In fact, Toyota uses open diffs and relies on traction control primarily to shift power.

    Are you sure or you it's your guess? Forget Toyota, does the Subaru traction control affect the Front/Rear power split ratio?
  • chelentanochelentano Posts: 634
    >> It's hard to have an intelligent conversation about AWD if you cannot acknowledge the difference between a Torsen and a Haldex.

    It's hard to have an intelligent conversation about AWD if you say that VDC is AWD.
  • kdshapirokdshapiro Posts: 5,751
    My credible link is Mike the host. What credible link are you using? A 2003 NYT article.
  • kdshapirokdshapiro Posts: 5,751
    It's hard to have an intelligent conversation about AWD if you say that VDC is AWD.

    Did you review the video posted? Here is a short course on AWD. AWD is an acryonym for all wheel drive. There are many variations of AWD, but it refers to the ability to have any or all wheels powered at the same time. How many wheels are powered at the same time and under what conditions are all implementation details and there are many different ways of accomplishing the end of keeping a vehicle moving. However, some ways are better than others.

    The terms for this are on-demand and part-time. In addition some systems give the ability to lock the f/r ratio. However the use of this is very limited and usually results in system damage if used on a non-slippery surface.

    In addition, some systems can vary the f/r ratio based on acceleration and deacceleration. Other systems can vary the f/r ration based on accelerator position. Some systems assist with LSD (limited slip differential), others assist with the anti-lock braking mechanism. BMW for example, does both.

    Having said that Subaru has multiple types of AWD systems. The ones we are debating are the one attached to the automatic. 2009 has a different system than 2008 and earlier. 2008 and earlier always power 4 wheels. According to the information presented there is always fluctation between front and rear from 80/20 to 20/80. Mitsubishi as Subaru is not very forthcoming with information about their AWD system. But much of that functionality seems to be based on accelerator position or slippage. 2006 Outlander models and earlier seems to be at the level of the RAV4/Highlander, which incidentally call their systems 4WD.

    I'm not 100% clear on 2009 Subie system yet, except that I'm guessing any one wheel can power the vehicle.

    I hope this short explanation helps with some of the terminolgy and concepts. Feel free to ask additional questions.
  • paisanpaisan Posts: 21,181
    Obviously we are bench racing here discussing stuff rather than actual real world use. I've worked on 100s of Subarus, raced them, and have many many contacts inside Subaru as well as Subaru Engineering. I didn't just make up the 90/10 to 10/90 numbers from the top of my head. Believe me if you wish or don't.

    This is my final post on this subject.

    However the statement from Subaru that Bob referenced was actually from a marketing guy who may or may not know the engineering behind his statement.

    -mike
  • kdshapirokdshapiro Posts: 5,751
    Believe me if you wish or don't.

    Just to set the record straight, I have been following these forums for a bit and by your posts I know you know what you are talking about.

    It's not me who is questioning the veracity on the information given on the Subie f/r split.
  • paisanpaisan Posts: 21,181
    It's not me who is questioning the veracity on the information given on the Subie f/r split.

    I know, just was responding to the thread in general. It's sad that I am here to help folks, yet some refuse to believe me. Frustrating at times actually. :(

    -mike
  • rshollandrsholland Posts: 19,712
    However the statement from Subaru that Bob referenced was actually from a marketing guy who may or may not know the engineering behind his statement.

    More than marketing; Mike McHale, being the Corporate Communications Director, is ultimately responsible for anything that SOA sends out to the public in terms of product and corporate information. I'm sure anyone in that position will make sure they have their facts straight before making pronouncements.

    Could he be wrong? Of course. He's human after all. Still, knowing how important AWD is to the brand, I'd put my money is on him being correct on this point.

    Bob
  • ateixeiraateixeira Posts: 72,587
    Well, untill they revise it, we not going to make stuff up and we use the available info.

    I've offered up some new info - the FWD mode for the Forester.

    Remember, you were the one that said the Outlander could go 100/0 because of its FWD mode, right?

    For the same reason, the Forester can, to.

    I'm using your own rule to prove that 100/0 is possible, so the 90/10 limit cannot exist.

    Let me find a photo of the instrument panel with the "FWD" mode lit up...I'll share if I can find one, otherwise I'll take photos myself next time I see a Forester. I'll go ahead and get the photo of the trailer pre-wiring since you didn't believe that either.
  • ateixeiraateixeira Posts: 72,587
    It's hard to have an intelligent conversation about AWD if you say that VDC is AWD

    VDC is just a marketing term, and Subaru did use it to describe the integrated systems on the early Outback VDC and Tribeca.

    They stopped when they started offering traction/stability control on other models.

    It's confusing, yes, but they did use the term VDC early on.

    By the way, Nissan has used the name VDC to describe its AWD system.
  • ateixeiraateixeira Posts: 72,587
    Paging wwest, paging wwest.

    I'll try to find him. :shades:
  • chelentanochelentano Posts: 634
    >> My credible link is Mike the host. What credible link are you using? A 2003 NYT article

    Post by Mike or Joe or whoever on some message board is not an evidence. I already posted many links from credible publications. Mike said that 80/20 split was only on 1998-2000 4-speed auto Subaru.

    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.
  • chelentanochelentano Posts: 634
    >> I'm not 100% clear on 2009 Subie system yet, except that I'm guessing any one wheel can power the vehicle. I hope this short explanation helps with some of the terminolgy and concepts. Feel free to ask additional questions.

    Why would I ask questions someone form a message board who is "not clear yet" and who is "guessing"? I would rather get some credible sources.
  • chelentanochelentano Posts: 634
    >> Believe me if you wish or don't.

    Well, "believing" in this is appropriate for someone who is into Subaru religion. So, yes, some would believe.
  • chelentanochelentano Posts: 634
    >> More than marketing; Mike McHale, being the Corporate Communications Director, is ultimately responsible for anything that SOA sends out to the public in terms of product and corporate information. I'm sure anyone in that position will make sure they have their facts straight before making pronouncements.

    Great point
  • kdshapirokdshapiro Posts: 5,751
    Why would I ask questions someone form a message board who is "not clear yet" and who is "guessing"? I would rather get some credible sources.

    No need to rely on my knowledge, just check out the video. I'm guessing the 2009 Forester will be able to accomplish the same thing. Have you looked at the video.

    BTW, I feel the same regarding one who uses a 2003 NYT article as the gold standard. Doesn't really matter, the 2009 Forester seems to be racking up a number of awards, and for good reason.
  • paisanpaisan Posts: 21,181
    An aside, my guess is that wiki, NYT, and the other "credible" sources, all are feeding off each other to get their facts.

    -mike
Sign In or Register to comment.