I use the number 83 because I have always liked the number, and also because it has my 2 favorite numbers 8 and 3. The #8 for Dale Jr. and the #3 for the intimidator Dale Earnhardt.
Number 18 is my number, it stems back to Codemasters' V8 Supercar (or Toca/DTM/Pro depending on your location) Race Driver where the number was used by the protagonist, Ryan McKane. There's a piece of nostalgia for ya.
8 for me as well. It's not lucky or has any real importance to me. It's the number worn by my favourite football (soccer) player. Paul Gascoigne. Hence why it features in my GTP name