You need a dyno where the rollers front and rear are mechanically linked to fool the car it is on normal road otherwise there is a difference of resistance which the cars computers try to compensate for and basically wont run.
Copied from a dyno description
"The key to designing an AWD dynamometer properly is to understand the methods currently being used by manufacturers in the field of AWD drivetrain technology. A dynamometer that can accommodate various types of AWD vehicle transmissions and wheelbases without excessive complication and, more importantly, without risking damage to a clientâs AWD system is paramount.Full time AWD vehicles are designed to provide maximum performance regardless of road conditions. In cases where traction is less than ideal, a vehicle may be designed to improve stability and traction at the expense of power. This means adding torque to a spinning wheel or retarding of timing. In order to properly test an AWD vehicle for peak performance, an AWD chassis dynamometer must be able to simulate ideal road-load conditions to the vehicle. This approach allows the vehicle to be evaluated under âoptimumâ operational conditions; whereby torque is distributed to the vehicleâs tires in the same manner that would normally occur when a vehicle has equal traction at all four drive wheels, and is therefore operating at peak efficiency.
To achieve this, Mustangâs AWD-500 Series incorporates an internal drive system that synchronizes the front and back rollers to simulate a flat, dry road condition. Synchronization, or linkage, insures that the front and rear rollers are always spinning at precisely the same road speed. This process eliminates the possibility of activating a vehicleâs traction control system and also insures that a vehicleâs torque management system is operating under the assumption that the vehicle is not skidding, turning or slipping."
