bike leg
n.— «Casati, like many other bike riding University of Montana students and faculty members, has gotten into the habit of rolling up a pant leg—or two—in order to keep it from catching in the bike chain. […] This fashion statement, known to some as “bike leg,” has made it easier to spot bikers on campus, sometimes even when they’re not riding.» —“Save your pants, use a ’geek strap’ while biking” by Steve Miller in University of Montana, Missoula Montana Kaimin (Missoula, Montana) Mar. 26, 2009. (source: Double-Tongued Dictionary)