NRG-500 is the fastest bike in Grand Theft Auto: San Andreas. The bike is based on the Yamaha YZR-M1 as used by Valentino Rossi in the 2004 Moto GP Season, hence the distinctive number 46 on the front. Since it's a racing bike, it also handles the best. Great for both on- and off-road, although it can't use its full potential off road. When using this bike in races, it is so powerful that it will automatically do a wheelie. It is also the best choice for evading police and doing unique stunts. When using this bike, you have a better chance of getting an insane stunt bonus than if you were using a different vehicle.(?)
It appears only in 3 places: In front of the bike school if you have all golds and in the warehouse in San Fierro docks, where it's associated with one of the vehicle challenges. Lastly there are two in a carpark on East Beach in Los Santos, the carpark has a spiraling ramp so its easy to spot.
The NRG-500 spawns at the Easter Bay Airport, in between the two southern most hangars near the Maverick. Jumping from the tunnel in the mountain, you can almost land exactly where it spawns. This is actually how many players find the spawning point.
Grand Theft Auto IV
The NRG-500 does not exist in GTA IV but there is another bike with a similar name, the NRG-900. The NRG-900 has proven to be the fastest bike in GTA IV.