I was just playing Arcade Mode, in which i have the Viper Concept unlocked. I raced Trial Mountain, and i really have to say it has to be one of the best cars in GT3. Not once did i loose control of the car, not even a blink from the ASM indicator.
thats simple just win all golds in S-license or do what i did go to pro mode and enter the Gran Turismo All-Stars series race thats were you can unlock the Viper concept