Hi Allen,

I really enjoy your reports. Your know your stuff and know how to write.
Sorry, if my questions have already been asked, then, please refer me to the right places.

1. Why superb time trialists like Dave Z and C. Boardman who weigh no more than some accomplished climbers and who can produce very respectable w/kg don’t seem able to apply it in high mountains?

2. Ignore this question if it’s inappropriate. But I think being involved with the cleanest team in the sport, you are uniquely qualified to answer. Besides…curious fans want to know. Can careful analysis and comparison of wattage profiles and VAMs from different races point to oxygen-vector doping or at least suspect one?

3. Is it fare to compare the wattages you report with SRM derived wattage by adding 10-15 watts? IOW, is the difference in measuring principle still applicable and not compensated?

Thank you much.

David from NYC.

Hi David -

I think can answer your first question with an excerpt from a 2007 Q & A session with Allen...

Allen explains:

Beyond power-to-weight or drag, there are other important physiological determinants of being a GC contender. These factors include a rider's economy (i.e., efficiency — energy burned for a given power output), his ability to repeatedly sustain high power outputs in the 30 min to 60 min time frame (something that is very different than a single all-out time trial effort), and his day-to-day recovery ability. That all said, it’s also important to realize that most riders I know have no desire whatsoever to be GC riders. Fortunately or unfortunately, there are only a handful of riders in the world with the genetics and desire to win Grand Tours. I think in our culture we make too much of those very few riders and sometimes neglect the heart of the cake for that icing. In the end, it’s the wide variety of talent and skill that make up the peloton — the climbers, time trial specialists, sprinters, super domestiques, and GC contenders — that make the Tour so amazing.
(http://www.saris.com/t-PowerTourQA.aspx#cancellara)

In regards to your questions about the SRM...

It is fair to compare the power readings of a PowerTap and SRM as first principle measurements of RPM and Torque. However they are measuring slightly different things. The PowerTap measures power to the road, and the SRM measures power to the crank. The difference between the two readings should be based on drive train efficiency which ranges from 98.5% to around 88% depending on the drivetrain and bicycle. (Single speed bikes have the highest efficiencies, internally geared hubs have the lowest.) Assuming an average drivetrain efficiency of around 95% and a ride between 200 and 300 watts the difference should range between 10 and 15 watts. There can be pretty large discrepancies in this due to a whole number of variables, but 95% is reasonable average. For more information on this, the book Bicycling Science by David Gordon Wilson has several lists of experimental data based on gear ratios and power, but not based on chain alignment.

The difference in measuring principle is not compensated because in a racing situation, power to the road compared to heart rate and perceived exertion are as important as the power number we use as our max sustainable output. For example, one of your gears likely gives you 98% efficiency and another one gives 91% efficiency based on chain angle. During a tough climb where riders are exerting themselves to the utmost, a rider producing 380 watts by the SRM could have a 30 watt difference in power to the road with the same power measured, just by changing gears. This translates to an extra 1.2mph for most sustained climbs. The PowerTap is able to show that there is more useful power being produced in the more efficient gear. Watching the power numbers you're putting to the crank is not perfectly indicative of how fast you are going. In the same vein, watching power numbers to the road is not perfectly indicative of how hard you're working. Each method has advantages and drawbacks. The PowerTap numbers are not compensated because they are accurate enough for fitness measurement (due to variability in your body from day to day) and they give more accurate numbers for people training to be fitter and faster.

Thanks, Rachel and BJ!

BJ essentially confirmed my recollection about the differences between SRM and PowerTap. It serves to caution any one attempting to compare wattage values from different riders using different systems.

I’d be thrilled if Allen finds few minutes to address my second question.

Thanks again,

David.

David,

Theoretically, this is a real possibility and quite similar to the biological passport program, where we look for unusual or statistically unviable changes in one?s blood profile or performance. In my mind, this is the ultimate bottom line in detecting doping. The problem is for this to be statistically viable, we would need all the power data from a given athlete. I mean all. Every day of training and every race. This may be possible as the technology improves and something we hope to begin experimenting with next season.

Allen