Instructions
Get in a speed car. The game's vehicles are divided into six categories, including stunt cars and aggressive cars. Speed cars are the only ones that can get boost chains.
Drive through a gas station to fill your boost bar and immediately execute a boost.
Launch your car off a ramp or other uneven terrain to perform a stunt. This will refill your boost bar again. Continually do this until you reach another gas station. Your goal is to use a boost at least once every 10 seconds to keep the chain going.