Explain to me how the Audi AWD system is the "best" when there are the SH AWD from Honda/Acura and Subarus (which has a higher % of their AWD cars still on the road than Audi).
I will be referring to the Quattro system here as the traditional one found in the most Audi models, not the Haldex-TT and VC R8 models.
The original Quattro system was superior to its contemporary rivals because it used 3 LSD Torsen differentials along with locking center and rear diffs. This allowed pro-active instead of re-active transfer of power, as well as a greater transfer of power between each axle/shaft. This setup proved to be very reliable.
There were some notable drawbacks, it was heavy, it was expensive, and it forced the engine to be mounted way ahead of the front axle, placing much weight on the front axle and adversely affecting handling.
Speaking in recent years terms:
Subaru and SH AWD use a method that sends the majority of power to the FW, and then, once a wheel begins to slip and the center diff detects it, can send a portion to the rears, usually up to 40 or 50%. The system is effective no doubt, and is cheap, reliable, and compact making it easy to package and sell. However, it maintains the mannerisms of a FWD car at the limit.
Most regular Quattro models feature a 50/50 f/r split with some of the sport models in recent years coming with 40/60 split (to help provide less understeer.) This provides a neutral feel and allows for up to 85% of power to be switched to either axle(may vary slightly by year/make). It also transfers the power before slip is detected.
On the other end of the spectrum is X-drive and 4matic which are RWD-based and then provide FWD assist when slip is detected. These observe the driving dynamics of a RWD car for the most part.
Now, under normal ideal driving conditions, there is not much difference between competing systems. In fact, most people driving regularly probably couldn't tell.
(The following is my opinion)
However, when driven in slippery conditions like ice/snow (which is the reason most people will be buying AWD sedans) it is very easy to tell them apart. The viscous coupling and FWD-based system's power transfer is jerky and non-linear, hard to hold at the limit, and unpredictable, which is an inherent trait of the system. When cornering, the vehicle will understeer slightly, and then as the center diff reacts will abruptly oversteer.
The Quattro system, being entirely mechanical, provides a very linear, very predictable power transfer to the wheel with the most grip. The result is an easy to control car once conditions are slippery (and its the most fun as well).
Of course, for straight line traction in deep snow, all other things being equal, the system with the best ability to transfer power will be superior (Quattro). This is really only in theory, though, as its very hard to replicate.
(Note - I have not driven every single car with AWD, and every year they seem to get better)
