Dr Mark Jermy and his team are using the Canterbury University wind tunnel to analyse airflow and drag as high-speed wind moves over cyclists. For cyclists to reach their potential, each one needs wind tunnel time to find what works for them in terms of body position, equipment and bike set-up.
Measuring and observing
Analysis of cyclists involves measurement of drag values as well as observing airflow using a small length of cotton thread.
The first thing to do for a cyclist in the wind tunnel is to measure the drag and analyse the airflow of their baseline position (the position and bike set-up they normally use).
- Drag measurements – once the wind tunnel is turned on, the air flows over the cyclist at up to 45 kilometres per hour. A graph of drag can be analysed by the scientists and coach. It is also projected onto a screen in front of a cyclist. Any changes in drag can be observed immediately. This helps the cyclist get a feel for what is affecting their drag.
- Body position – a light is projected on to the side of the cyclist and a shadow is seen on a whiteboard. This image is traced around so that any changes to body or head position or bike set-up can be visualised and recorded.
- Tuft wand – a small thread attached to a narrow rod is held over different parts of the cyclist to see whether the air is a laminar flow (flowing in smooth layers) or turbulent flow (swirling). If a point is found where the airflow changes from laminar to turbulent, this shows where the airflow has become separated. A change in body position, clothing, helmet or set-up may help to keep the airflow more laminar to minimise drag.
Less aerodynamic drag for faster race times
To give an idea of how much difference can be made by recommended changes to position and equipment, here are some examples of changes that have been trialled for some cyclists. This shows how much the change will affect the aerodynamic drag and finishing times of some cyclists:
- Wearing shoe covers – 0.11 seconds faster for each lap of a 250 m cycle track (at 420 watts power).
- Lower hand position – 0.40 seconds faster for each lap (at 420W).
- Taping loose hair – 0.18 seconds faster for each lap (at 300W).
- A simple change of helmet may reduce drag enough to make a difference of 4 seconds for each minute during a race.
One competitive cyclist changed to a lower body position, used a disk rear wheel and wore a body suit (as well as a few other minor changes), and this resulted in a reduction from 3.15kg effective drag down to nearly 2.7kg. These changes will result in significantly faster speeds during a 25km time trial and shave minutes off the finishing time.
This is some of the research that has been done by Dr Mark Jermy, PhD student Lindsey Underwood and others at the University of Canterbury wind tunnel to find what produces the least drag for different cyclists:
- Different types of helmets and the angle the helmet makes with the back.
- Effect of different body positions.
- Changing hand and thumb positions on handlebars.
- Wearing skinsuits.
Cycling races are often won or lost by milliseconds, so every slight difference in drag is important. Any reduction in drag by using a different position means that the cyclist will be able to bike faster, as long as the new position is still comfortable and allows them to produce the same pedalling power.
The current platform in the wind tunnel does not rotate, so drag measurements are only useful for cyclists riding directly into the wind. This is relevant for track cyclists or for road cycling on a relatively calm day. It is hoped that a rotating platform will be installed to allow realistic side wind measurements. This will be very useful for road cycling.
Nature of Science
Scientists often work in cooperation with others to find optimal conditions. Cyclists want a cycling position that minimises drag and still allows them to maximise their pedalling power.
In the Individual pursuit graphs activity, students cut out and tape different shapes, attach tiny pieces of cotton thread and use hairdryers to find which shape has the least drag. The shape that keeps airflow attached for longer reduces the low-pressure zone at the back, so it will have least drag.
Investigating airflow over shapes activity requires students to investigate their own drag and rolling resistance on bikes.