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Thread: The AWD debate

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  1. #21 Default  
    If you have an awd system with 2 open diffs, and I have a limited slip for 2 wheel drive, the amount of power that can actually be put down is very similar. Except the 2 wheel system has less losses.

    And as for losses, it's not about dyno, it's the fact that you have more moving parts with more fluids and lubricant that will create more drag in the system. It's a less efficient way to put power down from an energy efficiency standpoint.

    I will maintain my point that AWD is shit. Because even going car by car, I can point out why factually each system is compromised to say the very least, if not outright useless. and I am being overly generous here.

    You can keep detracting it from being a technical discussion I guess. But when I discuss each individual system, you will just say I keep changing the argument. But in fact each bits and pieces I'm breaking down per your request adds up to the overall point I'm making anyhow.
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  2. #22 Default  
    Now shall we discuss another type of useless AWD system, otherwise known as Haldex?

    Being a reactive system, where unless you have wheel spin, it's 95% torque to only front wheels, making them essentially FWD unless you are already understeer at speed. Or if you are at a standstill, front wheels are have zero traction, power is then send to the back where rear wheels are typically open diff with electronic lock for Audi or VW. If you want me to describe further why this one is junk, let me know.
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  3. #23 Default  
    Quote Originally Posted by cheu_f50 View Post
    No I didn't acknowledge incremental traction gain. You can't have traction gain. It is physically not possible. You can put power down earlier, but that's not traction gain. Traction is limited by tires, not drivetrain. FWD/RWD/AWD all have the same traction. It's about how to utilize all available traction for 4 wheels. AWD attempts to spread torque over 4 wheels instead of 2, and in selected situation the power distribution could potentially be more even, but that is not always true, in many cases it isn't more beneficial. This is why torque split is key.

    Why am I talking about open diff? Because Subaru uses them. Chris' car should have limited slip rear, open front, and viscous coupling between front and rear. Non wrx or sti uses open both front and back with viscous coupling in the middle. But I could be wrong. Depending on the configuration, you don't get all or any of the benefits associated with AWD.

    Like I said before. Not changing the argument. You keep pulling bits and pieces out of context.

    When you have torque that would exceed the grip of 2 wheels, being able to put power down to 4 when you are able to split torque let's you put more of it to the ground. The amount of torque you need to break traction in situation that isn't starting from zero mph is tremendous.
    I am trying to say the same thing. You don't have more traction, maybe you are just maximizing the traction that you have by applying the power via four contact patches rather than two. RWD is a less efficient way of applying power to the road from a traction maximization standpoint (devils advocate).

    Don't care about subarus or comparing one system to another.

    Plenty of cars can break traction at > 0 mph

    You can point out ways in which every car ever was compromised.
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  4. #24 Default  
    You ready for torsen center locking AWD system, used on some of the sportier Audis? Like on the S4 you had?

    It's actually probably the best of the bunch. The mechanical center locking diff doesn't require slip to happen before torque is transferred, unlike a viscous coupling design.

    But the downside is a weight distribution of nearly 60/40. You said steering feel is subjective? I'll say it isn't. Because the way this system the S4 works is that you have open front and rear diff on the axle. The braking system applies brake to the spinning wheel to transfer torque to the other wheels.

    Is steering feel quantifiable? Maybe not, doesn't mean it is not a factor. If you are telling me the computer applying brakes to individual wheels doesn't have a factor in steering feel, well let's just agree to disagree.

    You know what else you should agree to disagree on? engine Efficiency losses. Because to me, if you have a braking system that would apply to wheels when you are under power, to me you will always have more losses than a system that does not apply brake to transfer torque.

    What other system shall I discuss?
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  5. #25 Default  
    You can discuss as many as you want, you have already conceded to me the only points I cared to make.
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  6. #26 Default  
    Quote Originally Posted by Big Pete View Post
    You can discuss as many as you want, you have already conceded to me the only points I cared to make.
    Which is?

    And I guess I have made mine. you had no actual argument. Everything I said about why AWD is useless isn't something you can refute.
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  7. #27 Default  
    You admitted already it had several uses. Therefore it is not useless. How do you not see how this works?
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  8. #28 Default  
    How are you so thick? It's a compromised system. When you lose more than you gain. You are better off without it. it's useless.
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  9. #29 Default  
    Quote Originally Posted by cheu_f50 View Post
    You are better off without it.
    Quote Originally Posted by cheu_f50 View Post
    it's useless.
    Two totally different statements.
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  10. #30 Default  
    Anyhow you don't have anything to actually contribute, or refute, or support or argue against over the subject matter. you just want to argue to argue. So yea. good job. You win. Whatever it is you think you won.

    Meanwhile I'll continue to discuss why AWD, and it's flaws, make it the biggest joke of the last couple of decades.
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  11. #31 Default  
    Quote Originally Posted by Big Pete View Post
    Two totally different statements.
    And both are accurate.
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  12. #32 Default  
    There sure are some fast AWD cars for how big of a joke it is.
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  13. #33 Default  
    Good counter point Pete. There are fast car in all shape and sizes. But you can absolutely attribute fast cars to AWD if you want to.
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  14. #34 Default  
    Are you capable of thinking outside of absolutes?
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  15. #35 Default  
    You bring up absolutes. Not me. You are unable to accept a general statement. When I make a statment, you have issues with a understanding the big picture. Don't turn this around on me.

    You keep picking on singular points and then when I address specifics you say I move the goal post.

    You are all over the place with no argument.
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  16. #36 Default  
    How do I have no argument. You say it has no use. I say it has at least some use. How can I possibly be more clear?
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  17. #37 Default  
    This is akin to me calling a losing team a team with an under .500 record. You are arguing with semantics that the team which has loss more games than win isn't a losing team because it has won some games.

    And guess what, you may come back with the statement to counter me by saying what I'm stating is more akin to calling a team winless. and we go back and forth about wording. Because useless to you means absolutely, literally no use at all. To me, useless is a word I'd use for when you give up more than you gain. This is not the subject of matter in any case.

    Don't you get it? You don't disagree with me. You just don't like my wording. You try your hardest to vary my specific wording to have me "contradict" myself, but at the end of the day I'm still making the same statement, to which you still don't like my wording.

    It's not an AWD discussion you are having with me.
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  18. #38 Default  
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    My outback on allseasons is almost infinitely better in the snow than my FR-S with snow tires. On days this past winter where the FR-S had a hard time making it up the driveway, the outback barely drive any differently than it did on dry pavement.

    I am a pretty good driver in the snow, to the point where I could take the scion out in just about any weather. Driving the scion requires either taking risks or getting stuck. I don't get stuck. At intersections where there may be snow deposited by plows, I need to maintain some momentum in the scion to get through. This may conflict with the wishes of stop signs.

    I don't need to take risks in the outback and also never get stuck.

    As to AWD's performance advantage, I think the main one is that it allows you to drive a sporty modified car year round.

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  19. #39 Default  
    Jesus why did I just read that pissing match.

    Cheu, you keep saying that you'll only see the advantages at 10/10ths, which is not true. I need to draw some force diagrams, but I can't while at work. But lets say this: very often in my car while driving at roughly 7/10ths you can "feel" the front getting pulled through. When I say this I mean you feel the car rotating differently than a RWD car. To throttle rotate a RWD you need the tires to start to exceed their grip level so that they walk sideways more. This rotates the car by shifting the rear. With AWD you can instead "pull" the nose. If you look at from a force standpoint, with RWD, the front wheels will be undertseering just slightly anytime you're turning. It's just how the forces work pushing the tires against the angle they're turned. The only two forces on the tire are the car pushing forward, and friction backward. Those split over the steering angle and some of the force goes into friction, some goes into the direction of steering. The wheel "understeers" because it's not completely rigid and it tends to walk slightly towards the outside of the turn, similar to light throttle steering in the rear. You don't really notice it because it's so minute, but it's happening as a reaction to the forces on the tire. AWD adds a force at the contact patch in the direction the tire is turning. This helps reduce that pushing.

    In my car you can feel the initial pull on the nose, and then as you add more throttle you can feel the back rotate like a RWD car. Or if you're just a bonehead and wrench the wheel while going WOT you'll find colossal understeer because you have no finesses.

    AWD is absolutely a benefit for acceleration. Tires have a limit to the amount of power they can transfer. Putting power through all 4 means you can put down more, even with "weight Transfer" (which is more of an exaggerated misnomer than anything). There's a reason the GTR can launch so violently.

    Snow again.
    You mentioned cars with open diffs and why would you want that over RWD. I would rather have a car that is driving a single front and rear wheel than driving both rear if I'm in a situation where I might get stuck. Simply because there is a greater chance that there is more grip at one end of the car than the other. Lets take Justin's example of the snow deposits across a road near an intersection. In a lot of situations the traction on the other side of the deposits is better because it was freshly plowed. With RWD, if you don't carry the momentum to get those rear wheels across, there is a risk you will stop and get stuck. However if you can get the front over and let the front now pull on the better surface, there's less chance of getting stuck.

    The advantages in snow are very similar to the advantages on dirt, sand, etc. The more varied wheel positions you can put power through, the better your chances of not getting stuck.

    But lets talk about the downsides. First drivetrain loss. If you really cared, you'd buy FWD, because that has the least loss of anything. Every car is different, every system is different. I am willing to bet there are some RWD cars with the same loss as some AWD. There is no hard and fast rule that all AWD is 20%. If it bothers you to lose that extra few %, then that's a personal preference on the cars you want to drive. For me, losing that extra is worth the winter advantages. (that's personal, not fact)

    Unsprung weight. This is all about moments of inertia, how much a shape resists chances in rotational speed. The more mass further away from the rotational axis you have to get spinning, the more it affects your acceleration. However it's not as simple as taking total mass of everything, that's not how moments of inertia work. If we approximate everything as a perfect cylinder (it's close enough with wheels and axles), the moment of inertia is equal to (m*r^2)/2. Do the math for a 7kg (15.4lb) wheel with a 21.59cm radius (17in diameter) and you get 1631.4kg*cm^2. Pretend for a minute that an axle weights the same (it does not, it's less), but it has a radius of 3.175cm (1.25in, trying to balance the thin center with wider flanges at the ends). that's a moment of inertia of 35.282kg*cm^2. That's two orders of magnitude less, for something with the same mass. That's why the more popular spec miata wheels (they have a mandated minimum weight) were designed in such a way that most of their mass is in closer to the center. The outer barrels are thin, the outer section of spokes is thin, and the center is very thick.

    So what is really added with AWD? Two axles? Some gears in the center/front diff? I bet you can counter that simply by putting on lighter wheels.

    Steering feel. This one comes down to the car. Some car makers just have terrible steering in general. A lot of people really didn't like the new electric steering in the 991 because it felt so much more muted. I hated the steering in the ISF, and honestly think the steering in the WRX is better. However here I could go down a different rabit hole and say that power steering is terrible because it ruins steering feel and nothing will ever live up to the steering feel in the Elise with it's manual rack. Every car is different here and you can't make a blanket statement that all cars with AWD have worse steering feel than all cars with RWD.

    I'm sure there are more points to make, but i need to do a little real work this morning.
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  20. #40 Default  
    dont have time to debate this today in full. maybe later this week ill pick it up again.

    the front cannot pull in anymore than the direction of the angle of the wheels. if you have the wheels turned 10 degrees as an example, regardless of drivetrain, if you have ample traction (aka no understeer) the car will turn the same amount. From an engineering stand point, lets discuss this specific point when we have time without getting distracted with everything else. Because what I am saying is the whole "pull in" thing is part mental, part feeling, and not engineering.

    The open diff thing is purely down to preference. To say open diff AWD is better isnt any more valid than saying RWD with limited slip is better. You say you'd rather have 1 front and 1 rear. I say you'll end up getting stuck if you have one side of the car on the shoulder of an icy road or many winter parallel parking situation. As such, it goes back to what I have been saying - AWD doesnt offer benefits. It offers trade offs. Having the ability to power either left side or right side, is literally no better than being able to drive both rear (or both fronts assuming the fronts are not open diff). you just end up with different scenarios where one works and the other doesnt.
    Last edited by cheu_f50; 09-22-2015 at 09:38 AM.
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