SLK wheels are categorized as very rare with painted variants. They are items that you can collect and use to modify the battle car that you own. However, you will not receive any specific advantage during the match because it is only cosmetic. There is a chance for you and other players to get those items at random from the Overdrive Crate. Or, you can trade 5 rare objects from the same place. Not only that, you are able to exchange it with other people.