I think it's important to note that there are predominantly black outlaw motorcycle gangs, just as there are predominantly white outlaw motorcycle gangs. There are also predominantly black motorcycle events (Black Bike Week on the East Coast, Half Way Run on the West Coast) just as there are predominantly white motorcycle events (Bike Week on the East Coast, Sturgis in the Midwest).

That said, white gangs vastly outnumber black ones, principally for the same economic and social factors that continue to divide white and black today. As a 2014 paper published in the Western Journal of Emergency Medicine stated:

"... [Outlaw Motorcycle Gangs] are almost entirely white in the U.S., with the exception of the largely Chicano Mongols MC. Many outlaw bikers are racists, and there are strong links between the respective cultures of outlaw bikers and white supremacists.

Black OMGs exist, but these groups operate within a different milieu and have their own symbols and values. OMGs composed of African American or mixed-race members are less extreme in their entrepreneurialism and organization compared to OMGs composed of white members, and do not use the Internet as much as white OMGs do. Most black OMGs are local or regional rather than national or global in their reach, and are usually encountered on the East and West Coasts of the U.S. ... Sports bikes are often used among members of black OMGs, but sports bikes are anathema to most white OMGs. While members of white OMGs in the U.S. are required to have a Harley-Davidson motorcycle, the use of Harley-Davidson motorcycles varies among black OMGs. Although black OMGs are repressed by most white OMGs, affiliations between these two groups do exist. For example, the Baltimore-based Thunderbirds MC answers to the Pagans MC."

Most motorcyclists aren't members of a motorcycle club. Fewer still are members of what is known as outlaws. In the late 1960s, the American Motorcycle Association declared that 99 percent of motorcyclists were law-abiding. The remaining 1 percent were outlaws, and in the years since, they've embraced that status. You'll see patches that say "1 percenter" if you head out to a rally like Sturgis (though that event has moderated to a large extent).

Motorcycle gangs remain uncommon. In 2013, the FBI's national Gang report estimated that 88 percent of gang members in the United States are members of street gangs, 9.5 percent are in prison gangs, and just 2.5 percent are in motorcycle gangs.

In 2005, William Dulaney wrote a well-cited paper giving a concise history of OMGs/OMCs in the United States. I'm going to refer you to it, because it references the most widely cited works on the topic.

To summarize Dulaney's summary, he traces motorcycle development back to the cycling clubs of the early 20th century. While cycling clubs were popular among black Americans, and motorcycles were initially a cheap alternative to the automobile, they rose in price rapidly. By the mid-1920s, a full-sized Indian or Harley Davidson sold for about $375 at a time when a new Model T Ford was $545. This put motorcycles out of reach for most Americans, let alone black Americans, who tended to be poorer than their white counterparts because of endemic employment discrimination.

During World War II, large numbers of powerful, reliable motorcycles were produced for the war effort. Thousands of Americans were trained to ride and drive them, and many more discovered them on their own. In the years after the war, motorcycles were relatively cheap, thanks to war surplus, and Dulaney hypothesizes that Americans interested in returning to fond memories of the wartime era were likely to turn to motorcycles as an affordable way of outdoor recreation. Common interests allowed for connections and growth.

In 1947, outlaw culture was born when an American Motorcycle Association event in Hollister California turned raucous over the July 4 weekend. While Dulaney argues that media coverage of the event (newspapers and Life Magazine used terms like "terrorism") was overblown compared to the facts, the surge of attention gave motorcycling a counterculture flair.

Motorcycling remained relatively cheap and available to Americans who otherwise couldn't afford transportation. In a widely cited 1980 paper, J. Mark Watson asserted that outlaw motorcycle gangs came about as an outgrowth of lower-class cultural concerns. Those concerns included displacement by the "other," whether that "other" included black Americans or (at the time) Japanese imports (represented by a distaste for foreign-built motorcycles).

The opposite is the case in New Zealand--here most gang members are Māori (indigenous Polynesians) not Pākehā (white, ethnic European). See Māori gangs and Pacific youth gangs.

Ethnic gangs began to form in the 1960s as Māori became urbanised and lost touch with tribal communities. Various explanations exist for the formation of indigenous and ethnic-minority gangs, including: intergenerational impacts of colonisation; social exclusion; cultural alienation; economic deprivation; institutional discrimination and racism; and bonding through a sense of common identity. Unlike some overseas ethnic gangs, which limit membership to a certain ethnicity or nationality, Māori gangs may recruit from other ethnicities.

To be clear, are you referring to one percenters (i.e. outlaw biker gangs engaging in organized crime), or the legal motorcycle clubs?

Not directly answering OP's question, so I will remove this post if requested, but a great read for the layman about OMCs is Hunter Thompson's Hell's Angels. While it touches peripherally on African American clubs, it has many flaws. It's dated, written at the moment in history when the Angels were just entering the public consciousness, and is as skewed as any piece of "Gonzo Journalism" is. Nonetheless, it's a great read and explains lots of the basics about the culture (1%, patches, etc).

Also amusingly, it's actually categorized as an anthropology text by the Library of Congress instead of as journalism, at Thompson's insistence I'd wager.