According to the search results, the roller coaster with the most g-force is the Tower of Terror at Gold Reef City in Johannesburg, Gauteng, South Africa, which can produce up to 6.3 g of force. The Shock Wave at Six Flags Over Texas in Arlington, Texas, USA, is the second-highest with 5.9 g of force. It is important to note that the g-forces experienced on a roller coaster can vary depending on factors such as the weight of the train, the speed of the ride, and the design of the track.