Many racing games feature a large roster of different cars for the player to choose from, but often at the outset a player is limited to only several cars to choose from. Some games allow players to upgrade their cars with parts purchased with in-game currency. These parts can include new tires, engines, turbos, transmissions, or even whole new cars. Other games allow for the player to earn new cars or other upgrades by completing assorted in-game challenges. Gamers that consider themselves to be completionists often will not rest until they have every car upgraded to its fullest potential.