Originally Posted by Retro Grouch

The obvious answer is that it depends on the direction you are headed relative to the sun.

White reflects light all across the spectrum. Since every force produces an equal opposite force, the light bouncing off of a white bike will give it a slight propelling factor. Whether that makes it faster or slower depends on whether you are faceing into or away from the sun.

Black, on the other hand, absorbs all light rays and so has no such propelling (or ******ing) factor.

To maximize your speed if you have a white bike you should ride westward in the morning and turn around at noon to ride home. If you have a black bike you should ride eastward until noon.