This is a pretty easy achievement to get. You can do this easily anywhere, but I would recommend one of the super speedways, so Daytona or Talladega. Set the opponent to whatever difficulty you can use while still keeping up, and make sure you qualify for the race in the middle of the pack. Now just keep yourself behind someone. You'll know your drafting if you here a sound for the wind, or see the wind going around your car if you have that on. You should accumulate 1,000 yards before you do the first lap that way, so just finish the race, and you will have gained 15 easy gamerscore.