They were given out at Spooky Street during the 2015, 2016, 2017 and 2018 Halloween Events to go along with the Witch's Broom Kart and the Bat Kart. They were also given out during the 2017 Ready, Jet, Go! Back to Bortron 7 event by Gus.
Many users want these wheels and are asking how to get them, and many new users are happy that they have gotten more opportunities to get the wheels.
These wheels are transparent, so they do not seem to appear on the user's avatar.