From the Super Mario Wiki
The Mushroom tires are a set of unlockable wheels in Mario Kart 7. As their name suggests, they are wheels that are shaped and colored like mushrooms. Their best strengths are their speed and handling, while their acceleration, weight, and off-road are hindered. These are one of two tires in Mario Kart 7 that do not return in Mario Kart 8, the other being the Red Monster tires.
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