The grenade launcher feels useless because spaces are so large and empty, meaning you have to
hit enemies directly with the grenades in order for it be marginally effective, assuming the wonky physics choose to play ball with you.
However, in order to turbo boost or be in the zone; players must fill turbo meter units singularly or all four units respectively by drifting, driving on two wheels, driving backwards, aerial tricks, drafting cars
directly ahead,
hitting enemies with weaponry or side bashing cars, although drifting, driving on two wheels and driving backwards accurately through a blue speed strip offers a bonus towards filling a turbo meter unit, alongside collecting turbo boost cans.