There are just as many Tri's with small to average dicks. The myth of the bigger black dicks is just a result of repeating a lie until people accept it as truth. Combine that with the fact that black guys with anything less than huge dicks are not hired in porn and you perpetuate the stereotype. Truth is, the size range within blacks is just as varied as real humans. It's just that every black guy with a huge cock tries to make money off it.
As a gay black man Tri, I'm sure you've seen as many average black dicks as you have big ones.