Mario Kart Wii Cheats

When the countdown starts wait till the 2 starts to disappear and then press and hold the 2 button. So the 2 must still be visible but disappearing.
This will give you a boost at the start of the race.

When you see the POW block on your screen and its about to hit you, just do the function you would normally use for a trick to create a shockwave for youself to become immune to the spin out the POW block creates (Control panel on GCN controller, Shaking Wii wheel, etc.). This can be done on both bikes and carts. Even though you don't loose speed or spin out, you still will loose the items you were carrying.

Go into the Mii Channel and change your Mii drivers weight, which will have an in game impact causing you to change weight class and have different cars.

When you fall into something, such as water or falling from rainbow road, when you land, if you hit 2 at the moment you hit the ground, you get a temporary boost.