Pocketbike Racer

This Achievement is more time-consuming than challenging. There are 12 tournaments to complete, four in each of the three classes (50cc, 100cc, 150cc). The classes get progressively faster as you go upward.

Standard Race - Points are awarded based on your position at the end of your final lap. Weapon power-ups are available, and the AI use them to, so this can actually be the most difficult to win based on the wildcard factor.

Cone Trial - Be the first to pass through 20 gates in order to earn the maximum points. The rest of the pack earns points based on how many gates they passed relative to the other competitors once somebody hits 20. You don't have to finish ahead of the pack here, just get the gates first. At the start of the race, turn around and go backwards. You won't be competing for gates until you hit the midway mark, and soon the early gates will start to re-activate.

Battle Royal - Points are earned for hitting your opponents with attacks. Use the shield, and let opponents run into you. It's easier than hitting them with straight-fire rockets or waiting to earn enough charge to fire a homing rocket.

Hardcore Racing - It's basically the same as a standard race, but without weapons. Pick a bike with good acceleration and handling, and you should be able to out maneuver your opponents and win most of the races quite easily. Without the threat of getting picked off by rockets on the final lap, you'll find this tournament easier to win than the Standard Race.

Adding to Vermin's guide, I want to add that you must get 3rd, 2nd, or 1st in all tournaments.