With the Tour de France going through some dramatic mountain routes, we've seen some some unconventional descending positions, as riders aim to gain every second of free speed they can muster. Here's what aerodynamic experts have to say about the pros' super tucks, and some tips on refining your own.

“Cylinders. That’s what slows you down,” says Ingmar Jungnickel, aerodynamics R&D engineer for Specialized Bicycles. “Bike fitting is often focused on the rider’s back, but what we learned in the wind tunnel is that legs are 50 percent of your total drag.”

The quest to minimize drag from the body’s “cylinders” - legs, arms and head - has caused pro and elite racers to assume awkward aero positions on big descents, like Chris Froome’s famous top tube-sitting Stage 8 tuck at last year’s Tour de France.

“Everyone has two giant tree trunks going down to the frame,” explains Chris Yu, Specialized’s director of integrated technology. The idea is that “by sitting on the top tube, you’re bending your legs and reducing the height and surface area exposed to the wind, which cuts resistance and saves time.”

And looks alone would say that the super tuck is the fastest position. But it turns out one position isn’t the fastest for everyone. “How efficient you are is really a combination of shape and size,” says Yu. “And what’s best for an elite racer is really hard to generalise. We can’t just say the smaller you make yourself the better; your shape is equally important, and how your shape interplays with your size and your frontal area - how big a parachute you are - is hard to predict. There are general rules of thumb when it comes to aero, but there are always exceptions,” said Yu.