Prior to the GTO reintroduction in 2004, Pontiac showcased a more extreme-looking concept in 1999, with blocky styling far removed from the Holden Monaro body used in the current GTO model.
While the concept car sported 19-inch wheels in the front and 20-inch wheels in the rear, the car had no engine or drivetrain to power them, and was strictly a design-concept piece.
Source: www.seriouswheels.com