Obtain a bike and head for the airport. Go to one end of the runway, and start to accelerate. While doing this, pull back on the to start you wheelie. Keep going as far as you can, and then let your bike down. If you made it far enough, the achievement will unlock, if not, return to the end and try again. The runway works best because you have a very long distance where you can drive perfectly straight without worrying about cars pulling in front of you. It is also important to note that performing a wheelie is easier on a slower bike, such as a moped style bike, so if you're having trouble maintaining a wheelie, seek out one of these and you may have better luck.
**Can be done after completing story mode**