I think you need to punch up the biker: she's the focal point. The scroll is just the explanation, for the spectacle. Nobody can see your mind blowing lines like that. All the visceral grit and feel good dynamism can't give the eye proper visual nourishment in that scale. Certainly not at a distance. A lot of the imagery is pretty standard iconic fare for a racing premise: what's going to define it is the racer.
Also, I'd lose the pocket. It fractures the image more than any wrinkle could.
This is a mock up so I'm guessing it's nothing's carved in stone? No t-shirt bought yet? It's not a bad design. It's good; but I really gottuh say it could be greater if you blew up the biker. I'd buy the fuck out of that comic and that shirt.