Tire

A tire is a customizable vehicle part that appears in all the Mario Kart installments, but are only customizable in Mario Kart 7 and Mario Kart 8. It alters the speed, acceleration, and weight stats. The tires have changed constantly throughout the two games, varying in size and features.

Mario Kart 7
The tire customization first appears in Mario Kart 7. It, as usual, affects the speed and weight of the vehicle.

Mario Kart 8
Tire customization returns in Mario Kart 8. The stats didn't change much from the last game, but in anti-gravity the speed and handling are affected. In addition, all tires in Mario Kart 7 except Mushroom and Red Monster return, plus more customizations.

Trivia
The Standard, Roller, Slim, Slick, Wood, Monster, and Gold Tires are the only tires that appear in both games.