LEGO part 88517c01 - Dark Bluish Gray Wheel 75mm D. x 17mm Motorcycle with Black Tire 94.2mm D. x 22mm Motorcycle Racing Tread (88517 / 88516) at BrickScout
Amazon.com: Eske Kouri Gobricks GDS-1340 Wheel 75mm D. x 17mm Motorcycle Compatible with Lego 88517 All Major Brick Brands,Technical,Building Blocks, Parts and Pieces (26 Black(080),40 PCS) : Toys & Games