Instructions
Place a fire Pokemon that has either the flame body or magma armor ability in your battle party, such as a Slugma, Litwick or Magmar. If you keep a Pokemon with this ability in your party, the amount of steps needed to hatch an egg will be cut in half.
Equip your bike by pausing the game and selecting "Bicycle" from your backpack.
Press the "B" button to turn on the fourth gear of your bike. This will make the bicycle go faster.
Ride the bike back and forth from east and west. After about 10 minutes, you will receive an event telling you that the egg is hatching.