Maybe next year you’ll want to run in the marathon instead of watching it on TV. You’ll need some snug performance sneakers like the ones at the newly opened Asics flagship across from Bryant Park. It’s the footwear company’s first freestanding store in the U.S., and it comes stocked with a fancy I.D. system that measures your foot’s length, width, arch, and “ball girth.” After you hop on a 3-D scanner and a treadmill rigged to assess your gait, out comes a very precise recommendation for shoe size and style (51 W. 42nd St., nr. Sixth Ave.; 212-354-1908).