Regular users of CPL will be familiar with our efforts to evaluate pro rider's time trial performances in quantitative terms, especially estimated average power output and realised Watts/m^2 CdA (the power to aerodynamic drag ratio). We’ve been doing this for a while, since 2011 in fact, and in many ways this is the time trial equivalent of the climbing Performance Analysis made popular by others such as our friend on Twitter @ammattipyöräily. You can access this analysis in the World Tour category of our Popular Event Models (see the Results Analysis tab).
How does it work? Well, the first requirement is a GPS profile of the course. Then we factor in riders finishing times, height and weight estimates, atmospheric conditions, and our computer model is almost there. Almost…because we don’t know the rolling resistance of riders machines or their aerodynamic drag metric, CdA. The approach we take is to estimate a Crr of .003, about as good as it gets for high quality race tyres or tubulars on tarmac, and then we use “anthropometric estimators” established by empirical research to estimate CdA from rider's height and weight.
Now some people point out that this CdA estimate will introduce error, and it does. But the reality is we don’t really care. Why?.. Because our goal isn’t to calculate rider's power output, rather to “solve" the Watts/m^2 CdA achieved on the course. Within the range of error we get very similar results, whether or not we over/underestimate CdA and consequently over/underestimate power. More importantly these estimates have proven to be an excellent predictor of future time trial performances, within a few seconds from one event to the next.
So what do we make of the Bergerac Time Trial? Well, the first thing to note is that this event was run off under very light winds, a nice environment for Performance Analysis. Estimating Tony Martin’s CdA at 0.222 metres squared we compute an average power output of 477 watts and a “Watts per CdA” of 2147 Watts/metre^2. Martin is almost certainly more aero than that and his power in the final, long time trial of a grand tour was almost certainly lower...but the benchmark Watts/CdA stands. Only the top 3 riders seem to have broken the significant and indeed World Class 2000 Watts/CdA mark. Meanwhile 1700 Watts/CdA was good enough for 50th place.
How fast would you or an athlete you know have gone on this course? Use the Power & Pace tab on the same page to find out!