A digital tachometer is used to determine the surface speed of a rotating work piece in surface ft/min. Tachometers are designed to read rotational speed in rev/min, but in this case the shaft of the tachometer is directly coupled to a wheel whose outside rim is made of rubber. When the wheel rim is pressed against the surface of the rotating work piece, the tachometer provides a reading of surface speed. The desired units for surface speed are ft/min. What is the diameter of the wheel rim that will provide a direct reading of surface speed in ft/min?