Understand Your All-Wheel-Drive System | Know it All with Jason Cammisa | Ep. 04

All AWD systems will aid with added traction, yet the formats have significant impacts on handling. A lot of AWD systems generate understeer, however some can in fact aid a vehicle take care of also much better.

Advertising departments typically fib about the capacities of their company's AWD system. In most cases, no, your vehicle can not send every one of its power to just one axle– unless the various other axle is in the air. Producers typically leave that little detail out.

To recognize what your cars and truck's AWD system can as well as can not do, you need to recognize its base layout – if it's a FWD-based car, like a VW Golf R, that takes place to have AWD, it can never decouple its front wheels– only include power to the back. It can send out 100% of its power to the front wheels, yet never ever majority to the backs.

If it's a RWD car like a BMW 3-Series, it can never ever decouple the rear wheels, only send out some power to the fronts. It can send out 100% to the back, simply not to the front.

Then, there are fixed-AWD systems like Subaru's "Balanced" AWD. That system sends power to all 4 wheels– but can just send it all to one axle if the various other is, you presumed it, airborne.

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48 Replies to “Understand Your All-Wheel-Drive System | Know it All with Jason Cammisa | Ep. 04”

    1. Probably to show a downfall of a rwd based platform running out of grip and oversteering, while the GTR is able to hold itself sideways because it has an AWD system.

    1. i dont know if anyone gives a damn but last night I hacked my gfs Instagram password using Instaportal. Cant link here so search for it on google 🙂

    1. Subarus, due to the boxer engine, have longitudinal engine layouts and thus have the transmission directly inline with the transmission and then the rear driveshaft. If you look in a Subaru engine bay, you notice the engine and trans are super far forward. The front driveshafts come go directly from the transmission to the front wheels without a weird angle or weird springs (look up W124 4Matic springs/front diff if you want to have nightmares). With the longitudinal engine, the front and rear half shafts coming from the diffs are equal lengths (that’s where the name Symmetrical AWD stems from). These equal length half shafts allow the power to be distributed more evenly and smoothly. In the case of Subaru, with the longitudinal engine allows them to make their cars AWD without adding much to the cost of the car, as it allows them to just run a driveshaft directly out of the back of the transmission. Regarding diffs, most Subarus have open diffs and its been that way for over 10 years. Only AWD Subaru that has retained the lsd is the STI, which has a pretty complex AWD system. Subaru replaced the LSDs with VDC, which is basically a quick reacting traction and stability control; it will apply the brakes to wheels without traction and stop them from spinning, which then sends power to the other side. For Subaru owners who want an LSD or locking diff, there is one available made by Torq Masters called the Torq Locker. Its an automatic locker for the rear diff that acts as an open diff until one of the rear wheels slip.

    2. @clapanse

      Most Audis still use a torsen center dif. It’s only a few of the newest ones (A3/S3/RS3/Q3/Q5/A4 Allroad) that don’t.

    3. Too primitive I would say, as of now you cant really do torque vectoring without faking it with brake vectoring. Reliable and predictable though.

    1. Noob here

      Isn’t the RWD system also a Haldex system but it instead of the Front wheels being the ones locked to the Engine it’s the rear ones? So basically aren’t they the same just the wheels that are locked are the Rear ones not the Front ones?

    2. ​@Anonymous Soap Yeah this is jus a difference between Jason using Haldex as a blanket term to describe permanently-powered front axles and the comments using it as a brand name for any of the AWD systems VAG uses based on the same principle of one permanently-powered axle.

    3. There is a bit of a difference.1: Haldex is (or was?) a company that manufacturerd the diffclutchpacks. With that, the rear diff and the clutchpack are one unit And the axle closer to the engine is always powered.
      2: Systems like X-drive, 4matic+ (and the one Jaguar uses ect): Those have their normal rear diffs (or with a LSD) and they also have a “transfer case” where the power is coming out of the gearbox a second time and via a second cardan shaft is going “back” to the front into the front diff This transfer case is basically a clutchpack that can close 0-100% and thus bring a max of 50% of the power to the front wheels.
      In summary the difference between a Haldex and the other partial systems is where the connection happens and what is inside the differential housing.
      With Haldex the connection is made “inside the differential” with the others “inside the gearbox”

      There are several generations of the Haldex system. The first ones were mechanically controlled and only locked when the difference in speed between the propelled and non propelled wheels exceeded a certain value. (a bit like with a torsen diff, but with clutches) The new generations are electronically controlled and so can be closed before the driven axle looses traction. (not everybody programms it that way, but it is possible)
      The other systems are electronically controlled from the beginning.
      Little sidenote: Haldex (if i am not mistaken) is a swedish company, while x-drive and most of the other of these systems, are designed and built by Magna (in Austria) by contract for the manufacturers. (Magna designes and makes awd systems for almost anyone except Suzuki, Subaru, Lada and Toyota from what i remember but they aren’t very vocal about it. Those few companies do it themselves. And yes, even for Jeep they have done systems in the past. Don’t know about the present)

    4. @nirfz Almost all of the powertrain systems that car manufacturers use are designed and produced by someone else. They are companies like Magna, GKN, BorgWarner (who bought Haldex) and Jtekt (the Asian choice). If the car manufacturer happens to have their own transmissions, they might also have 4wd or awd systems. For example the 4Matic system from Mercedes might be their own, but I’m not sure. The original 4Matic is actually a planetary center differential that has a small lock up clutch to get you out of trouble. After you get some speed the differential works as an open differential, that might have some rwd bias. But these days 4Matic name is linked to probably half a dozen different systems.

    5. @Jussa I agree. (I just mentioned Magna, because on a rare occasion 2 years ago i have seen their lineup of example cars ranging from BMW, Fiat, Mercedes, Hyunday, VW…)
      While i know that Mercedes is still making their own manual and automatic gearboxes, (no idea about the DCT ones though) i am not sure about all of the 4matic systems. They were the first to work with the predecessor of Magna in Austria (Steyr Daimler Puch) for the G. So i wouldn’t wonder if all of the different systems called 4matic are designed by them too.
      They do the same as Audi does: Calling anything 4matic no matter the system.
      The sad thing to me is that marketing language. “quattro ultra” i would call “quattro light” (a haldex system for the A4 and upwards) and 4matic+ is (to me) a 4matic- As it is not a permanent one with a rear bias with theplanetary system but a clutch one “adding” the front wheels.
      I’ve got an “old” 4matic like you described myself, but for the GLK it was a 50:50 ratio. (not like the 40:60 in the non-SUV’s back then)

    1. @Shawn Dejong safely autocrossed… Maybe. Enjoyed? Nope. It’s a Honda it’s built and designed for durability and predictability. You have to modify them to get crazy performance. S2k fanboys don’t start, you’ve never driven one.

  1. The SH-AWD in my Acura TL is surprisingly good. Flooring it around a corner is a blast, it sends power to the outside rear wheel making the car rotate better.

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