Most people don’t consider riding a bicycle to be an extreme sport. But when the speeds exceed the national speed limit on a routine basis, you have to make an exception.  Great photos.

One segment of cycling has taken technology — and the performance it yields — to a whole new level. Fans of the World Human Powered Speed Challenge held annually in Battle Mountain, Nevada, find the top-of-the-line Tour De France mount positively archaic.

To propel a human-powered vehicle, or HPV, to 80-plus miles per hour, a rider needs more than a lightweight frame and some fancy wheels.

The fastest bike ever created won’t go anywhere without the right person to ride it. In addition to having great leg strength, the pilot must be small enough to fit inside these bullet bikes and have the proper mental stamina.

"At high speeds like we experience every year at Battle Mountain, a fight-or-flight reflex kicks in," said Sam Whittingham, a record-holding HPV pilot. "You have to have absolute faith in your equipment and be 100 percent confident that everything is going to hold together at Mach 3."

The designers, builders and riders who compete for top human-powered speed records rely on machines with features like wind-tunnel-designed bodies, a stiff carbon fiber monocoque chassis, video-camera guidance systems and computer-assisted steering.

In this era of HPV racing, high-powered fluid-dynamics software is almost more important than good training and a healthy diet for a pilot that is a gifted aerodynamicist.

"It will always hold true that more power to the wheels will yield greater speed," said Matt Weaver, a builder and designer of several winning HPVs and the current American 200-meter record holder.

"Currently, however, it is also true that gains in any one of multiple technical aspects can outweigh great differences in physical capability," he continued. "For a given rider, gains in training for an entire season will be readily exceeded by a few minor technical refinements."

Several HPV races are held across the country, but only two have major prizes for aspiring HPV racers.

The first is the $25,000 Dempsey-MacReady prize, which will be awarded to the first person to pedal at a steady 90 kilometers (56 mph) for a solid hour. That hasn’t been achieved yet, but the current mark is 52.57 mph, held by Sam Whittingham of Canada in the Varna Diablo speed bike.

The second is the $23,000 .deciMach Prize. This award will be given to the first HPV to exceed one-tenth the speed of sound for 200 meters. At sea level on a perfectly flat course, this is 75 mph. At Battle Mountain, the speed is adjusted to 82 mph to compensate for altitude and grade.

Whittingham is also the fastest man on Earth in this competition, having clocked a speed of 81 mph in 2003.

As recently as 2000, the top speed achieved was less than 70 mph. The huge jump in speeds in recent years comes partly from a better understanding of laminar flow aerodynamics. Laminar flow, or fluid dynamics, is when air flows in parallel layers with no disruption between them. And it’s nearly impossible to design a true laminar shape without the right computer software.

"With two similar-looking bodies, one laminar and one not, the laminar can have one-third the aerodynamic drag," explained Weaver. "That’s huge."

More here.