Subaru Tribeca - Drivetrain

Drivetrain

Subaru chose to use an aluminum alloy boxer engine in order to reduce powertrain weight. The Subaru boxer engines have a lower center of gravity than typical inline and V type engines, this helps reduce body roll. The weight of the engine and automatic transmission are balanced instead of being offset. The power delivery is also direct from the transmission to the front wheels, and to the rear wheels through a rear differential, which is limited slip on some models. The front differential is integrated into the Subaru transmission. Other AWD vehicles were first engineered as either front or rear wheel drive, but were modified with an additional, external transfer case and asymmetrical drive shafts to power the additional wheels.

The boxer design also provides near-perfect vibration mitigation because the movement of each piston is exactly countered by the corresponding piston in the opposing cylinder bank, eliminating the need for a counterbalance shaft, and that the movement of the pistons is on a horizontal plane. The only vibration caused by the boxer engine is secondary caused by the cylinders being slightly offset on opposing banks. This vibration, however, is minimal and is largely absorbed by rubber engine mounts. Torque steer is also reduced with this type of power train layout. This is achieved by having the front driveshafts being of equal weight and length, and extend from the transmission to the front wheels at almost perpendicular from the transmission.