Go to Free Play mode and rent the 2011 Bugatti Veyron Super Sport. In the "Race Setup", choose "Environments - Le Mans Circuit De La Sarthe" and select the "Old Mulsanne Circuit" track, which has the longest straightaway in the game. Set it to "1 Lap" and "1 Max Drivatars" on a nice day. Go to "Assists" and turn off the "Traction Control" and "Stability Control" options to allow you to reach a higher top speed. You can also use a manual transmission to reach an even higher top speed, but it is not required. Start the race, and get the car over 250 mph on the straightaway. Then, finish the race and do not use a rewind to get the "Two-Fifty" achievement.