Draw a rectangle around the frontal area of the motorcycle (including rider). The dimensions of this rectangle (L X W) equals total frontal area, which is one of the variables required for accuracy (and a very important one!)
The red rectangle illustrated in the attached picture is an illustration of this...
This is the main obstacle in achieving higher speeds, as the speed increases it takes exponentially more HP to "punch a hole" through the air.
The point of that is to calculate the surface area encountering friction at the front end of the bike? Using the rectangle that measures the highest point to the lowest on the bike and the widest points of the bike seems almost arbitrary. There has to be an accurate way to calculate the actual surface area.
To clarify, that picture you posted has a lot of blank/white space. It seems like that area is being counted as surface area.