Every June, racers gather at the bottom of the course in central Colorado and see who can get to the top the fastest. A simple concept, yeah. But a punishing one. The road to the top is 12.42 miles and counts 156 turns. It's a climb of 4,725 feet, some 500 feet shy of a vertical mile. The average grade is 7 percent. Internal combustion engines can lose up to 30 percent of their power between the start and the finish, simply because the air thins out.

Racers too, lose strength and reaction time on the brutal climb, sometimes with deadly consequences. Motorcyclist Carl Sorensen was killed during a practice run this week after crashing off the course near the summit, the sixth death in the history of the hill climb and the second in two years.

The course includes huge elevation changes and hairpin curves as narrow as 20 feet. In more than a few spots, going off-road means plunging off near-sheer drops.