You may find the explanation of Chase Mode in the link above. Here is a copy from the link.
"“Chase mode” functions to limit power output to 70% of full throttle. When the moment comes to attack, a push of the 3rd channel button on the transmitter increases power output to 100% for 3-second burst of speed. This enables greater driving control and also adds the excitement of overtaking duels so drivers can enjoy nose to tail racing battles. Also, the number of power boosts can be set to apply a handicapping system to level the playing field for drivers of different experience levels."