Bart perked up when the Batmobile started to gain on him and he looked back at Batman with a fierce, bright grin before lowering his head and flattening out his hands, leaning so far forward that if he had stopped suddenly, he would have fallen flat on his face. Bart made himself as aerodynamic as possible as his left foot fell. He began to push off of the ball of his foot with all of his might, ketchup and mustard colored stains rippling off his costume like the wake of a boat-- and then Grampa pulled up along side.
Bart frowned up at his Grampa and let the Speed Force slip away for now (it was never far) as he slowed back to a jog to let the Batmobile over take them, giving a forlorn look towards the car as it sped in front of them.