A vehicle (8) includes steerable front wheels (18), an interaxle differential (14) for transmitting torque from an engine (10) to the front wheels (18) and to rear wheels (22). The differential (14) includes a controllable clutch (24) operable to control a ratio of front wheel speed to rear wheel speed. A control unit (30) controls the clutch (24) as a function of sensed steering angles and stored information including steering angles and corresponding front to rear wheel speed ratio values. The control unit (30) is automatically calibrated. The control unit (30) periodically obtains steering angle values, periodically obtains front and rear wheel speed values, periodically generates new front to rear wheel speed ratio values, and replaces one of the stored front to rear wheel speed ratio values with one of the new ratio values if the steering angle values indicate that the vehicle (8) has been in a straight ahead travel mode for at least a certain time period.