Bonus tracks:
 
Successfully complete each tier of tracks in 
arcade mode on any difficulty setting to unlock
the next tier of tracks: 


Tier 1: 
Super Speedway, Midfield Raceway, Smokey Mountain,
Swiss Alps, Trial Mountain, Midfield Raceway 2.
 

Tier 2:
 
Smokey Mountain 2, Tokyo R246, Grand Valley Speedway,
Laguna Seca Raceway, Rome Circuit, Tahiti Circuit. 


Tier 3:

Swiss Alps 2, Trial Mountain 2, Deep Forest Raceway 2,
Special Stage Route 5, Seattle Circuit, Test Course.


by unknown