To get to the speedway, Maxwell needs a vehicle capable of withstanding the heat form the fire vents.

Round 1: Fireproof Motorcycle
Round 2: Cold Bike
Round 3: Fireproof Balloon (vehicle)

Scribblenauts Remix 12-9 Cheats Hints gallery:
12-9-1-a: Use Adjectives to provide Maxwell with a vehicle capable of withstanding the heat from the fire vents!
12-9-1-b: What’s the opposite of a hot car!
12-9-1-c: Create a cold vehicle.