Alternate Color
At the vehicle select screen, press R.
(Thanks to LWargalla@t-online.de)

China Town Jam Track
In the Grand Prix mode on Expert, finish first in each course.
(Thanks to LWargalla@t-online.de)

Dominator
Finish the game in first on Expert with the Black Lightning.
(Thanks to LWargalla@t-online.de)

Extra Tracks/Vehicles
Go to the title screen with controller 2. Then, press and hold Up on the D-Pad and press and hold R+DownC+L+Z, then release. Then, press Start on controller 1.
(Thanks to Myau84@aol.com, LWargalla@t-online.de)

Neo Speedway Track
Beat each course of the intermediate Grand Prix mode in first.
(Thanks to LWargalla@t-online.de)

Play As N64 Controller
In Time Attack mode, get a time that ends with .064.
(Thanks to LWargalla@t-online.de)

Prowler
Finish the Expert difficulty level in first with the Hornet car.
(Thanks to LWargalla@t-online.de)

Reaper
Finish the Expert difficulty level in first with the Shredder car.
(Thanks to LWargalla@t-online.de)

Secret Cars
Finish a race with a time of 64:00.
(Thanks to Myau84@aol.com)

Turbo
During the race, press and hold A and make a hard left while holding Z and release both buttons. Then, tap A or repeatedly.
(Thanks to Myau84@aol.com, LWargalla@t-online.de)

Turbo Start
At the starting line, press and hold A+B and release B after the announcer says Ready.
(Thanks to Myau84@aol.com, LWargalla@t-online.de)

Vengeance
Finish the Expert difficulty level in first with the Avenger.
(Thanks to LWargalla@t-online.de)