On... The Cycling Null Point

When cycling one constant is the movement of air.

You are moving through the air as you move over the ground and the air that surrounds you is probably moving too, as a breeze or wind (which if strong almost always seems to be a head-wind rather than a tail-wind for some reason). The relative movements of you and the air mass you are cycling through can sometimes make progress hard work but most of the time the movements are more subtle. You can hear a fairly light breeze as it moves past your ears, your eyes and nose can feel small air movements and your lips more sensitive still (especially if you wet them).

However, just occasionally, it is possible to experience a 'null point' where your movement through the air exactly matches the movement of the air surrounding you relative to the ground. At the null point you are moving but are in (it seems to you) completely still air, and not a trace of breeze can be felt. The sensation is strange and, despite cycling most days, is one that I have very rarely experienced and never for more than for a few seconds.

For a null point to occur, the movement of the wind must exactly match your speed and direction on the cycle, at least within your ability to detect any air movement caused by the difference. Experiments carried out in a closed room show that the face is capable of detecting air movements of less than 10cm per second but as the distractions of the road are likely to reduce sensitivity I will use this figure.

Next I will assume a fairly sedate average cycling speed of 20 kph (about 12.5 miles per hour). 20kph is about 5.5 metres per second. As a wind of 0.1 metres per second is detectable the moving air must be within the range 5.4 to 5.6 metres per second. It must also be blowing directly from behind otherwise there will be some movement across the face which will be detected – I would estimate that a wind within say 10 degrees of directly behind is undetectable.

Lastly, the wind (if there is one, remember absolutely still air will seem like a 20kph breeze on the bicycle) will have to be moving in a uniform direction and not swirling. When air is moving there is, however, usually some swirling or gusting but it is difficult to put a figure on how common this is. Suffice it to say a mass of air moving in a uniform direction and speed without any swirling or gusting for more than a few seconds is unusual. Of those winds that do, only a small percentage of will be in the 'right' direction and only a small fraction of those will be blowing at the 'right' speed. Which explains why the null point is unusual. So if you should happen to experience one then enjoy it while it lasts.