Black penis is the biggest. However, urbandictionary is a great example of how many people will vote up or down to represent their own race.
Black - biggest penis
White - next biggest
Indian - almost the smallest (whether Northern Indian caucasoid, or Southern Indian australoid).
Chinese - Smallest
While at an adult party Jenny says "Hey Tom, you cuckold, look how many guys with big black penis aka BBC"
Jeshmina "Oh why do Indian guys have such small penises. I wish I could get a BBC, but my small dicked husband won't let me."
Shaniqua "I'd love to go interracial, but only Black guys, and a few white guys have big enough dicks to satisfy me"
Me "Don't take my word. Just go to a few adult parties, and you'll get a good idea of the average size of guy's dicks"