US Choppers Boardtrack Racer Frame, A single cradle design and low slung weight distribution allow for incredible lean angles and an insanely fun ride on this frame. The boardtrack racer accommodates most ’39-later engines up to 124" including Evolutions®, Flatheads, Knuckles and Pans. Shovelheads do not fit. Provisioned for internal fork stops, rear aXLe and rear aXLe eccentrics. Two lower “boomerang” pieces sold separately.