The Stern (ger."Star") wheel is a collectable item in the game that is used to customize the player's vehicle further. It provides no advantages while used and is simply cosmetic. It is categorized as a common wheel but painted variants are categorized as exotic (uncommon before August 4, 2017) and can only be obtained by trade-up.
It cannot be traded to other players since every account will have one. However, painted variants can be traded.