I would imagine that power to weight ratio is more important than just the power. Also the smaller the cyclist, the smaller they can build the aerodynamic shell, thus reducing drag.
Air drag is proportional to the front facing area of the vehicle, that is 2nd power of cyclists dimension (for example, height, we are assuming that humans have approximately similar shape, regardless of size). Max power grows to 3rd power of cyclists dimension, because it's dependent on the cyclists muscle mass. Maximum aerobic power grows somewhere between 2nd and 3rd power, because of the fractal shape of lungs and veins (for example, think about lung surface area, the smallest folds in lung have same dimension in bigger and smaller guys, so the area grows faster than 2nd power of cyclist's dimension).
It then follows that bigger guys do well pushing against air (since frontal area grows slower than maximum aerodynamic capability), and smaller guys do better dragging themselves uphill (since mass grows faster aerodynamic capability).
You can easily find practical examples of this: say Fabian Cancellara, who has won time trial world championships 3 times + almost anything else riding in fairly flat ground, including several tour prologues and stages before getting into mountains... but when you get to the mountains, it's the featherweights that rule, so likes of Cancellara can't ever win the tour.
So... to propel something as fast as possible against air, you need big and strong cyclist (with huge lungs to match), just like the guy in the video looks like.
Power/weight has little to do with it, since air drag is most of the resistance, and they can accelerate for 5 miles before measuring speed (you would need power/weight if you needed to accelerate fast, which is not the case).
Actually, on a flat surface with a constant speed or acceleration, weight matters much, much less than frontal area. Weight comes into play much more when many quick accelerations or elevation gains come into play.
Because frontal area doesn't increase proportionally with weight, I would argue that power output should be the primary concern and that typically increases substantially with weight. For evidence of this, look at world class time trialists versus world class hill specialists.
Fabian Cancellara [1] is considered one of the top time trialists in the world at 181 lbs as he can put out much more absolute consistent power than someone like Nairo Quintana who is considered one of the world class climbers and weighs 128 lbs, [2] even though Nairo Quintana may have a better power:weight ratio.
Was wondering the same since, this is about top speed and not about acceleration the weight shouldn't matter much at all, since it has no direct influence on the air resistance.
Would be interested in knowing, if a human powered vehicle on steel rails with steel wheels with the same air resistance could be faster than this just due to the lower rolling resistance.
Weight shouldn't have as much of an impact on acceleration because as muscle mass & power goes up, weight goes up as well.
But more weight inside the shell doesn't increase air resistance, while it does increase power. So a heavier rider with greater sustained power output will, in an environment where wheel friction is trivial, go to a considerably faster top speed on flat ground.
Did anything happen to F = m × a in the last 20 years?
Acceleration a is heavily dependent on the mass m.
Since a = F / m having half the mass would result in double the acceleration with same amount of force F available.
If they're putting athletes into this thing, the bigger the athlete, the more force (okay, the more power) is available for propulsion. They have bigger muscles which store more glycogen and have greater total mitochondrial activity, because there are simply more of these cells available to do the work.
Unlike in high school physics, we have to account for drag, which is a lot more important than mass at these speeds. F=ma is true, of course, but you have to think more about what F really is.
