A prime example of the benefits of a near perfect aerodynamic position comes in the form of Bradley Wiggins - one of the most accomplished and decorated time triallists of all time.
Let's consider the position used by Bradley in the 2012 Olympic Time Trial:
We can ascertain that Wiggins has a frontal area of 0.372m². A figure which may be difficult to interpret in itself, especially if we consider that inevitably a taller rider will naturally represent a larger frontal area than a smaller rider.
However, if we normalise the frontal area as a ratio to the rider's height we can allocate an aero score of 19.6. This will give us a benchmark by which Wiggins' frontal area can be compared to other riders of different heights, or himself in different positions.
Given that we don't have access to any of Wiggins' previous ride data to calculate his coefficient of drag (Cd), we can use some standard estimates to make an assessment of the Bradley's CdA - in this example it equates to 0.223.
Frontal area: 0.372m²
Estimated CdA: 0.223
Aero score: 19.6
Estimated power : CdA (@470W): 2108
Estimated power : aero score (@470W): 24.0
Of course, it is interesting to try and verify our calculations by comparing these numbers with other values derived in different ways. We know that Wiggins rode the 44km course in a time of 50:39.54 on the day in question. It was widely reported that his average power output was in the region of 470W - we know, that Wiggins was in the form of his life in securing the Olympic gold medal only a few weeks after becoming the first British winner of the Tour de France. By plugging these numbers into a suitable online calculator the same CdA estimate of 0.223 is also returned.
Now, both methods of calculation include estimates and therefore some degree of error is expected in the absolute numbers. That said, it should be recognised that even a wind tunnel measurement of Cd is only applicable to the precise conditions of the tunnel, not the real world.
For any aerodynamic analysis it is more important that we can produce comparable results, such that these can be used to consider the impact of a different position. As an example let us consider the situation if Wiggins' frontal area were to increase by 3% - this alone would have led to a 30 sec increase in the time taken to complete the Olympic TT course (in the same conditions).
Note that a 3% increase could itself be achieved if Wiggins were to raise his shoulders by as little as 2.5cm. Such a change would result in a new aero score of 20.2, itself an extremely low value. In fact most riders would struggle even to match this more relaxed position, let alone Bradley's aggressively compact aerodynamic setup (and that's without even contemplating his phenomenal power output!).
We are also able to use our new virtual wind tunnel to examine the same position. Using another photograph (taken from the same ride) we can look at the impact of the body position on the air flow. The following video shows the effects of air whilst travelling at 30 mph:
We must consider not only the effect on the rider cutting through the air but also the air passing over the rider and any disturbances seen in the wake flow. We can see from the video that Wiggins has a very clean (as we'd expect) profile. One small area of interest is Bradley's seating position - it is not unusual for a time triallist to shift forward a little when applying effort, however, in this case it exposes the rear of the saddle which may cause minor disruptions in the airflow. Of course, this is somewhat subjective analysis but can be a useful part of the position review process.
So, in conclusion, we can measure and quantify Bradley Wiggins' aerodynamic position from just one photograph. We can verify the the data collected and then use it to examine the impact that small changes to his position would have on his likely times. We can also use a side profile view to examine the same position in our virtual wind tunnel, in order to check for obvious visual disturbances to the air flow.
You too can harness the power of bike aero data to evaluate your position and ultimately ride faster.