Roller

The Roller tires are a set of default tires in Mario Kart 7 and Mario Kart 8.

Mario Kart 7
The Roller tires are the smallest tires in the game, and they offer the best acceleration and handling boosts among all the kart parts. However, they also offer the lowest speed and weight boosts. Despite those flaws, however, the Roller tires strongly excel while underwater, and their air stats are given a positive boost too. They're also pretty stable when compared to most other tires.

Mario Kart 8
The Roller tires reappear in Mario Kart 8. Although they are still the smallest tires, they are red with a yellow center, instead of black with a silver center, like in Mario Kart 7. The Roller tires are still available to use right off the bat, but despite this, CPU players will never use them.

Much like in Mario Kart 7, the Roller tires offer the highest acceleration boost of all tires, but their handling boost is much less extreme than before. Fortunately, they don't hinder speed and weight as heavily as in Mario Kart 7, despite still being the slowest and lightest tires in the game. In terms of their hidden stats, the Roller tires have the highest stat total of all the tires in the game.

A variant of the Roller tires, called the Azure Roller tires, also appear in Mario Kart 8, where they share the same stats as the Roller tires. The Button tires also share the Roller tires' stats, despite having a different appearance.

Stat boosts
Stat values are out of 6.

Mario Kart 7

 * Speed: -0.75
 * Sea Speed: +1
 * Air Speed: +1
 * Acceleration: +0.75
 * Weight: -1
 * Handling: +2
 * Sea Handling: +1.25
 * Air Handling: +1
 * Off-Road: -1.25
 * Mini-Turbo: +1
 * Stability: +1
 * Drift: -1

Mario Kart 8

 * Ground Speed: -0.5
 * Water Speed: 0
 * Air Speed: +0.5
 * Anti-Gravity Speed: -0.5
 * Acceleration: +1
 * Weight: -0.5
 * Ground Handling: +0.25
 * Water Handling: +0.25
 * Air Handling: +0.25
 * Anti-Gravity Handling: +0.25
 * Traction: -0.25
 * Mini-Turbo: +1.5