Successfully complete the indicated task to unlock the corresponding car:

Carbon Hydros Custom: Beat all Showtime Road Rules. 
Carbon Ikusa GT: Beat all Time Road Rules. 
Carson Carbon GT Concept: Find all 400 Smashes. 
Carson Fastback: Get a B license. 
Hunter Mesquite: Get a D license. 
Jansen Carbon X12: Land all 50 Superjumps. 
Krieger Carbon Krieger Uberschall 8: Successfully complete two sets of Online 
Challenges. 
Montgomery Carbon Hawker: Hit all 120 Billboards. 
Nakamura SI-7: Get a C license. 
Rossolini Tempesta: Get an A license. 
Watson 25 V16 Revenge Racer: Successfully complete all Road Rage Events.