To drive the awesome NVR 150 RR SP, push the change view button while selecting a circuit. (Continue holding the button until the race begins.) Meanwhile, at the vehicle selection screen highlight these motorcycles in order, pressing the brake pedal after each:

Wild Hog
NVR 150 RR
Anthais
Wild Hog
Now highlight NVR 150 RR, mashing the brake pedal twice. The NVR 150 RR will be upgraded to the NVR 150 RR SP!