The average black penis is measured to be 6.1" erect, while an asian is only 5.5". Surprisingly, this survey puts caucasian men ahead with a whopping 6.5" erect cock*. Blacks fare better than whites in flacid measurements, however (3.7" vs 3.4")
Other surveys put Asian men into the distant third as well.**
Blacks 6.89" (175mm)
Whites 6.22" (158mm)
Asians 5.33" (135mm)
Also of interest:
...men were asked to rate members of their own ethnic group with respect to size. Of particular interest was the response of East Asian subjects. Among East Asians residing in the East, 31% felt that they were generally of modest size, compared to 56% of those living in the West. This is probably due to the fact that Western countries tend to be more racially diverse, allowing for greater interaction and hence comparison with men of different ethnic backgrounds. It is also interesting to note that the vast majority of Black subjects stated that they tended to be well endowed; an opinion which was not borne out by the results of this study.
* Source: Size Survey
. Due to the small sample size (I am not sure if the pun is intended) and large variation in lengths, this "difference" is not statistically significant.
** Source: The Penis