Originally Posted by grubincan
And this one is a lot of fun too, if you have an hour to spare....
AWD sistems wars (testing) on rollers - YouTube
It's surprising how many vehicles have trouble on a just pair of front or rear rollers (is that a BMW xDrive that can't get off a single rear roller?) it would be nicer to see some other makes and newer models.
None of this is too surprising. Most people get caught up in marketing rhetoric, and it's no surprise that people love Subaru's “Legendary” AWD system. Most of the vehicles in the video have open diffs for the front and rear axles (some of the newer vehicles are also backed by e-diffs), thus the lack of moving when front and rear left or front and rear right wheels are on rollers. E-diffs can be defeated when traction is very low. The only Subarus as of 2011 that use mechanical lsds in the front or rear axles are the STI models. The rest all have open front and rear differentials.
The only AWD system that fits the profile of “Legendary” by Subaru is the STI's AWD system and the the VTD AWD systems found on 4EAT GD WRXs and 5EAT 05-09 LGTs and Outback XTs. They all have a planetary gear center diff with a rear lsd (clutch type lsd on the WRX, LGT, XT, and 04-06 STI; Torsen T2 on the 07+ STI). In the STI, the driver has the ability to manually lock its center diff and manually change its degree off lockup. All STIs have a front helical type lsd. These systems, paired with a VDC (essentially e-diffs) are extremely competent systems which direct the most torque to the wheels with the most traction.
Now take the rest of the automatic transmission AWD systems. There's a mutliplate clutch in the center and acts proactively (many here have argued that it's not called a differential—I really couldn't care less about semantics). I have no problem with this system. My fiance owns a 4EAT Impreza. The clutchpack provides ample torque transfer between the front and rear axles and works fine as a daily driver. For the price of the vehicle, it's great, even though it's not the most technologically advanced unit. If it ain't broke, don't fix it. The front and rear axles have open diffs backed by e-diffs. I've never been stuck with this car, but I never had the opportunity to test it in really icy conditions as I don't drive it often. Nonetheless, for the price of the car, I know that it does what it's supposed to do. Is this AWD system legendary? I think it's just rhetoric when comparing it to other systems that I've driven in the ball-park price range. It's basic, but it's put together well. This system will probably fail a roller test whereby the left front and rear wheels are on 0 friction rollers on an incline. The e-diffs will most probably be defeated. I'll even venture on to say that it will fail the same tests in the video, minus the ones where the fronts or rears are on rollers. We know the clutchpack works fine. E-diffs can only do so much.
Now take all the manual tranny AWD systems. Having owned a 5MT 07 Leggy, I can tell you that it's absolutely awful. What I mean by awful is that it's simply the worst
AWD system that I've ever driven short of a completely open diff setup. The real joke is that it's pretty much the same as an open diff setup. I remember a thread called “5MT AWD=All wheels disconnected?” by sajohnson and his experience was exactly like mine. The 4kg viscous coupling diff is so awful at regulating any speed differences between the two axles that Subaru may as well have given us open diffs to save weight, as the VCU is useless with the sole purpose of increasing the car's curb weight. I swear to god, you can take any center diff on the market and it will be better than that awful piece of garbage found on manual models. Even the newer models with VDC are terrible, because the braking done by the e-diffs simply is not enough to compensate for the lack of lockup in the center diff.
The only reason I still own a Subaru is because I own a 2010 STI, which has a fantastic, albeit pretty old AWD system. I mean it really stomps face. That's the only high end AWD system provided by Subaru though, and I paid almost as much as a base Audi S4 for it.