Quick shifts:
Hold A while pressing the D-pad repeatedly to shift quicker.

Hint: Racing on ice:
On levels with ice, shift to gear 4. It will make a slipping sound. To avoid death, let off the acceleration. The noise should stop after about one second. After the noise is gone, shift down to gear 2 then advance to gear 4. Note: In solo course 5, the track has ice on every part. Sometimes there is a straight-a-way after the corner. If there is, you will not hear the slipping noise when you move left or right.