The design theme skateboarders often strive for is distinct from “rat bikes,” a breed that fetishizes matte finishes over glossy paint and rust over chrome. There is a “Road Warrior” quality to many skaters’ bikes. Mr. Eusey’s Harley, for example, has a hatchet bolted to the frame (handy when camping out) and foot pegs made from railroad spikes. But elegant flourishes often emerge: he recently repainted his gas tank in a psychedelic wild cherry sparkle finish accented by tiny flakes of silver and stripes of gold.

The crossover of skateboarding’s design culture to motorcycles has been embraced by Harley-Davidson. A promotional video for a new model in the Sportster line, the Forty-Eight, features skateboard heroes like Leo Romero, Heath Kirchart, Brian Hansen and Matt Ball. And the Forty-Eight  named for the year Harley introduced its first small “peanut” gas tank, according to Mr. James, the Harley public relations official  comes tailored with some of the styling elements favored by skaters and other young riders, including a solo seat, forward-mounted controls, a 2.1-gallon peanut tank  and it’s available in a matte black finish.

“The trend is certainly broader than skateboarding, but I feel like it started there  maybe it’s purest there,” Mr. James said, noting that the enthusiasm seems to have spread to groups like snowboarders as well. “Skateboarding could very well be the epicenter. There’s no question that there are huge parallels there between bikers and skateboarders.”

Max Schaaf, a longtime professional skateboarder and owner of 4Q Conditioning, a customizing shop in Oakland, Calif., is widely regarded as one of the most influential figures in skateboarding and custom bike building.

Mr. Schaaf hand-builds and paints his customer’s bikes, which can cost tens of thousands of dollars. Their elegance lies not in ostentation  this is not an overhyped chopper shop from cable TV  but in their minimalism. Every visible part seems to have an equally visible function; the pieces are as gorgeous and meditative as they are spare and athletic.

“The perfect bike is one where every part is exactly where it belongs,” Mr. Schaaf said.

It’s also an aesthetic that, like a Rodin sculpture, does not disguise its handicraft. “You do see the welds, you see where the pieces are put together, the weld just looks right,” he said. “Someone building a concours vehicle, they would never have a weld being shown.”

Such easy grace can be rebellious in the steroidal motorcycle culture. Mr. Schaaf’s spare designs make him something of an outsider in the biking world, while, ironically, drawing inspiration from 1960s biker gangs.