Explained: Superman position on bicycle

An explanation of how the seemingly impossible superman position on the bike without pedalling can beat the rest of the competitors pedalling hard.

Deepak Karkala
October 2019

Watch this video below and see if you can make sense of it.

What we see in the video ?

A cyclist adopts a crazy plank like position - hands on the bars, stomach on the saddle, legs extended behind. He begins to accelerate despite not pedalling. The rest of the cyclists are unable to match his speed even when pedalling furiously hard. So how does a cyclist in such a strange position without putting any effort outperform the rest who are all expending huge amounts of energy ?

This article aims to uncover this seemingly mysterious phenomenon by explaining the underlying physics involved in bicycling.

The physics of bicycling

Like all automobiles, a number of forces act against a bicycle and the cyclist must overcome all these forces in order to accelerate and pedal the bicycle forward. However unlike other automobiles where the engine provides the power, the power provided to the bicycle wheels comes from the cyclist's legs. The motion of the bike is caused by the rider pressing down upon the pedals when the power provided by the cyclist is higher than the forces acting against the bicycle.

So in order to understand the physics of bicycling, we must first understand all the major forces acting on a bicycle. Scroll down to know more about these forces acting on a bicycle.

Let us learn the major forces involved in bicycling.

Three major forces are involved while pedalling on a bicycle.

  • Rolling resistance
  • Gravity
  • Aerodynamic drag

Rolling Resistance

This refers to the friction between the tyres and the road surface. It includes the resistance created by the rolling elements of the bike such as gears, tyres, bearings. Bumpier road, lower quality tubes, tyres and heavy bike all leads to higher friction and therefore more resistance while biking.

One of the important factors determining the rolling resistance is the weight of the biker and the bike itself. Heavier the bike and the biker, higher is the friction. Alter the weight to see how you fare against a reference cyclist whose total weight with the bike is 80kg. Observe the realtive difference in the time taken to cover a distance assuming equal power is provided by both the cyclists.

Gravity

This refers to the force exterted by the earth towards the ground. If you are cycling uphill, you are fighting against gravity, but if you are cycling downhill, gravity works for you. Also heavier the bike and the rider, higher is the gravitational pull.

The slope of the path largely determines the extent to which the force of gravity works on a bike. Larger the slope, higher is the force to be overcome by the cyclist. Alter the slope to see how it affects gravitational force. Observe the realtive difference in the time taken to cover a distance assuming equal power is provided by both the cyclists.

Aerodynamic drag

This refers to the force exerted by the air against the cyclist while riding as both the bike and the rider need to push the air aside in order to move forward. At high speeds, this accounts for the majority of the force acting against the cyclist. The faster you ride, denser the air larger is the drag against the rider.

Both the cyclist and the bike present a certain frontal area to the air. The larger this frontal area, more air needs to be displaced, and larger the force air pushes against cyclist. At high speeds, reducing this frontal area has a significant impact in reducing the overall force acting against the bicycle. Observe how the time taken to cover a given distance varies with different seating positions of the cyclists assuming they all provide equal powers to the wheels.

The total force resisting the cyclist is the sum of these three forces.

  • Frolling: Rolling resistance
  • Fgravity: Gravitational force
  • Fdrag: Aerodynamic drag

Ftotal = Frolling + Fgravity + Fdrag

In order to overcome all these forces and move forward, the cyclist must spend energy. To move forward at velocity V (meters per second), energy must be supplied at a rate that is sufficient to do the work. This rate of energy expenditure is called power (Pwheel) measured in watts and is given by

Pwheel = Ftotal . V

We have now learned the forces invloved in bicycling. Let us use this to unravel how the superman position helped the cyclist to gain advantage over his competitors who were all pedallig hard in conventional seating positions.

Unravelling the superman position

To recap the video, the cyclist begins accelerating despite taking his feet off the pedals and lying flat on his bike. To further astonishment, he passes the rest of his close competitors who are all pedalling hard. Let us demystify this by inspecting closely the cycling aerodynamics.

Significance of reducing aerodynamic drag

Of the three forces we looked at, except at low speeds and on steep ascents, the aerodynamic drag is the major force acting against the bicycle. In fact at race speeds, aerodynamic drag can constitute up to more than 95% of the total resistance faced by cyclist. This is further illustrated by the graphic below where we can see that at high speeds, the power required by the cyclist is proportional to the cube of velocity.

So as we observe, higher the speed, higher is the drag and thereby higher the work needed to overcome this drag. At racing speeds, the drag is enormous and clearly reducing this drag is critical to save energy or go faster. Professional bike riders adopt a number of measures such as optimising shape and material of helmets, bikes, fabrics to minimise aerodynamic drag. Reducing drag is also the reason why racers stay in groups whereby the drag faced by someone in the middle of the group can be considerably lower than the ones at the front. But by far the most common technique used to reduce drag is to simply alter the riding position by dropping really low close to the bike. As we saw earlier, this reduces the frontal area presented to the air and has a huge impact on reducing the force exerted by air.

The superman position takes this very principle to its extreme. Despite the massive risk, the drag faced by this position is significantly lower compared to the other seating positions. In addition to the weird position, there are a couple of other factors that needs to be discussed. The first, while in this flat position, the cyclist has no access to pedals and therefore cannot impart power through pedals while in this position implying the superman position can only be effective while going downhill. Although not apparent, this is indeed the case in the video. The second, related to the first aspect, is the fact that the cyclist in superman position is riding a what is called as "fixed gear" bike where the pedals are rotationally locked to the rear wheel. This meant that when he took his feet off the pedals, it allowed the back wheel and thereby the pedals to spin free. In contrast, his competitors descending at high speeds in conventional racing positions faced much higher aerodynamic drag preventing them from going any faster despite pedalling furiously hard.

Why don't we see this position more often in racing ?

The risk-reward theory is prevalent in all sports. Higher the risk, higher the reward but the risk almost always comes at a price. Sportpersons are often faced by the dilemma of what price are they willing to pay for the risk. In this case, the cyclist adopting the superman position successfully outclasses his competitors albeit at significant risk. While in the position, the cyclist has no access to pedals and at such high speed even a slight imbalance may well result in horrifying and career ending crash. Considering this enormous risk, most riders would not dare to try this position. Nevertheless, the stunt did provide a lot of value in terms of entertainment and the lessons it offered. It certainly showcased the remarkable human spirit of trying to push the boundaries in order to gain a competitive edge in defaince of all the risks involved.

In case you missed the other notable moments in the video,

In addition to all the physics we examined in this post, there are a number of notable moments in the video including what appears to be a prayer before the cyclist adopts the superman position, one of his competitors pointing to him with an astounded look on his face, the person on the scooter taking both hands off the vehicle to take a photo of the superman. Perhaps the most intriguing moment is the cliffanger ending, does the cyclist successfully manage to get his feet back on the rotating pedals because since it is a fixed gear bike, if he didn't the bike might well have come to a stop further illustrating the complexities involved in adopting such a position. No wonder it is called the Superman position and yes "Do not try this at home".