First, you’ll need to purchase the Speedcross Story Bundle from the store. It will cost $7.99 USD ($7.19 USD w/EA Access) plus applicable taxes. The purchase includes the option to purchase the speedcross versions of the Infinity Q60 and the Mini JCW Countryman, which you cannot buy until completing this story achievement.
Upon starting the game after purchasing the speedcross bundle, Rav will contact you (you’re playing Mac). Rav will provide you a Mini Countryman that he’ll upgrade for you as you progress through 16 speedcross races. After competing all 16 races, you’ll be crowned the Speedcross Champion and the achievement will pop. You’ll also have access to the speed cross story to purchase (and upgrade) any of the speed cross cars. Good luck!