(Image: John Hart, Centre for Sports Engineering Research Sheffield Hallam University)

IF YOU’RE a keen cyclist, chances are your helmet and bike have been designed to reduce drag. If you’re a professional racer, you – or your team – will want to know the aerodynamic impact of everything, from the frame to the quick-release nuts on the front wheel. Computational fluid dynamics (CFD) is the hideously complex mass of equations that can do all this.

Unlike traditional wind tunnels, CFD allows engineers to identify the contribution to drag for each component. “We solve a series of equations that calculate, for any point in space around the cyclist, the velocity, pressure or whatever fluid quantity we desire,” says John Hart at the Centre for Sports Engineering Research at Sheffield Hallam University in the UK. Previously only available to affluent sports such as Formula 1 and sailing, as computing costs have come down other sports have become interested. Hart’s team helped British Cycling prepare for the Olympic Games in Athens and Beijing.

This image of a cyclist on a triathlon bike is a visualisation of the CFD calculations. Yellow and white areas on the cyclist and bike show regions that have the highest drag. The cyclist himself accounts for 72 per cent of the drag force, with his legs generating most of that. The frame and forks account for 5.7 per cent, and the gearing 5.2 per cent. Water bottles are lumpy and generate 4.5 per cent of the drag. External cabling makes up 3.8 per cent, which makes a strong argument for tucking it inside the frame. As for the ribbons streaming behind, the white lines indicate high-velocity airflow and the pink-blue lines indicate slow-moving regions.


As well as all this, the method also makes for a pretty picture. “CFD is perhaps the most colourful technique used in engineering,” says Hart.

This article appeared in print under the headline “Go with the flow”