You may remember, before smartphones, one very popular game called Gravity Defied. If you have played this game then Bike Race is the right choice for you.
The goal of the game is riding over many crazy maps and paths in the best time possible. Touch the display for acceleration and keep the bike on the wheels. The game contains many levels but the best part is the multiplayer through the Game Center. As you progress you get new bikes. The only negative is the advertisements.