The all-wheel-drive system is also significantly different than in the WRX and offers extensive driver adjustability. Even left to its own devices, the STI system is more sophisticated, with a default rear bias (41:59) and two different types of limited-slip differentials at the front and rear to apportion torque from side to side. The center differential's automatic mode can be finessed in two directions: Auto (-) makes for less center differential lock, aiding steering feel and making for more rear bias. Auto (+) creates additional center diff lock for better AWD performance in slippery conditions. As if that weren't enough, there's also manual mode, with six levels of differential locking. The rally driver's favorite is manually selected full lock, which works best for loose surfaces and improves braking, although it makes for heavier steering. That's the one we went with, as the track was rapidly becoming more like a rally stage with the sun melting the ice and the mud and rocks taking over. The looser surface and the higher speeds (thanks to the more powerful engine) just about negated the efforts of the more sophisticated AWD system, however, as we powered around the circuit. Still, it was interesting to swap back and forth between varying levels of differential lock, giving the car a more or less lively rear end.
The event really pointed up the differences between the versions of the Impreza. The STI is a very sophisticated machine, with probably more driver adjustability than most owners will fully appreciate. The WRX is still sporty but easier to use - and may be a more compelling choice for the coming model year, as Subaru is giving it the STI's wide-body styling. The base Impreza, which we also briefly spent time in, is the plucky, growling, little Subaru that best embodies the spirit of the first Subarus, which earned their reputation in the mud and snow.