Time Trial Mode can be found under the mode selection screen below Grand Prix. It allows racers of all skill levels to test themselves by racing on a track of their choice and seeing how fast they can finish 3 laps. This is also the racing mode where World Records are set.
There are no item boxes on Time Trials, but you are given 3 One-Up Mushrooms at the beginning of the race. If you fall off of the track, they will disappear and you will not be able to use them. This also happens when you have used all 3 of them.
Unlike Mario Kart 64, obstacles do appear on the courses during Time Trials.
- Shy Guy (skier and snowboarder) appears on DK Summit
- Goomba appears on the Mario courses
Because of the 3 One-Up Mushrooms that you are given at the start of a race, shortcuts are easier to execute than in a VS. Race. The mushrooms allow you to 'shred' or drive over grass without slowing down. This ability allows you to cut through corners a lot faster than usual, and even go through the game's premade shortcuts (ex. Coconut Mall Mii Shop Shortcut). Many people have also created their own shortcuts, much like the one on GBA Bowser's Castle 3.
 World Records
Mario Kart Wii includes a worldwide or continental Time Trial ranking system through Nintendo Wi-Fi Connection or Wireless LAN Connection. It allows you to upload your times to the Mario Kart Channel and see where you stand in the rankings. You can check your ranking using the format in the Mario Kart Channel, which looks like this:
Your ghost time stands as the highlighted gold one, with all related other ghosts (alternate profiles, friends, and rivals) highlighted in blue. The world record holder's ghosts is at the front of the crowd, also highlight in blue. The top ten for whichever ranking you are viewing (regional, worldwide) is shown in the circle with a picture of the number 10 and a crown. You can download these ghosts and race your rivals via Wi-fi connection. If you don't have Wi-Fi connection, then you will not be able to access this channel.
Ghosts are a way of recording your times and replaying them over and over again. If you choose to race one, a faint character will appear on the track and it replays exactly how whoever created the ghost raced. You cannot hit this ghost, or come in contact with it at all, but it is a very good guideline of which line you should take while driving if you want to beat your time.
 Expert Staff Ghosts and Staff Ghosts
Staff ghosts are ghosts created by the staff of Mario kart Wii. The default staff ghosts are created using the Wii Wheel, so their times are not very fast to begin with. If you beat the staff ghost time by a certain amount of time (ex. 5 seconds), you will unlock something called an expert staff ghost. You can tell if you unlocked it at the end of a race if in the bottom left hand corner it says 'A fast staff ghost has appeared!'. These ghosts are a lot faster than the original staff ghosts, they use shortcuts and were created using either the Nunchuck-Wiimote combo or Gamecube controller.
These ghosts are a good example for you if you are first starting out on a track and want to know how to race it properly, or when to use your mushrooms.
Related ThreadsTime Trials Strategies - last post by @ Aug 29, 2009
Hacker's Time Trials - last post by @ Apr 5, 2009
wut cc is wifi and time trial? - last post by @ May 16, 2006
Fingers of Fury - Time Trial Leaderboards - last post by @ Nov 12, 2008
Pit of 100 Trials - last post by @ Aug 13, 2012