At first blush, bicycling to the bottom of the Grand Canyon sounds like the ultimate gonzo bike trip, so, this is my recommendation: GONZO STAY HOME! This Excursion falls in the category of "touring bike" (with fat knobby tires). It is a challenging ride, but anyone comfortable and confident on two wheels can do it.
The point is to be surrounded by the grandeur; to take the time to look around and smell (don't pet) the cactus. Several stops are made to talk about the geology right in front of you, the changes in environment with the change in elevation, and the human history that stretches back thousands of years.
With very minor exceptions this is an all down hill bike ride ending at the Colorado River. People and bicycles will be driven back to the top. The elevation change in this part of the Grand Canyon is roughly 4000 ft. For any given time of year temperatures at the top are more or less those of Prescott, Az. and temperatures at the bottom are more or less those of Phoenix.