|You can operate the features along the surface of the course by Boosting on top of them. There are many different features on all of the courses!|
— Kirby Air Ride North American instruction booklet, page 11
Boost refers to the act of releasing an Air Ride Machine's charge in a sudden burst of speed in Kirby Air Ride. All machines are capable of charging and boosting except the Wagon Star, and among the machines which can boost, each has different power to their boost.
To perform a Boost, the player must first press and hold the A button to cause Kirby's machine to brake, building up charge. Once the charge meter is full, the player can then release the A button to boost at full power. Charge can also occur while Gliding, which will lead to a boost upon a smooth landing.
The machine with by far the most powerful Boost is the Rocket Star which - once released - causes the machine to move faster than any other standard machine unaided (barring some situations with the Bulk Star).
In City Trial, the Boost Patch increases the power of a machine's boost, which in turn leads to greater post-boost speed and acceleration. Additionally, the Charge Patch will decrease the time needed to charge for a boost.