On Bicycles, and.... what else is there?

When you think about power meters what professional team comes to mind? Only one... Indeed, there's a web site devoted to photos of Chris Froome looking at stems . Staring at his SRM display, many have claimed. Sucking the humanity of out racing by reducing it to pre-programmed efforts determined by power analysis? Hardly, obviously, but traditionalists always oppose change. He even does it in Pro Cycling Manager , a video game: So it's a major change in the world as we know it when it's leaked that for 2014, Sky is discarding their trusty SRMs for Stages power meters: Stages measures power on only the left leg, assuming the right leg is the same. This, not surprisingly, results in errors. I looked at Stages power data in this blog post . For example, comparing Stages power / 2 to Vector left-leg power is a good match, according to DC Rainmaker's data: But compare it to the Vector right leg data, and things get uglier: It typically takes two legs...

The cleverest way I've seen to check cadence data is due to Robert Chung. He uses cadence and speed in conjunction with an assumed wheel rolling circumference to calculate the for a bike for each data point. If cadence and speed were measured perfectly, I'd be able to see exactly what gear the rider was in at every point where he was pedaling (no coasting). On the other hand, if the cadence or speed are measured sloppily, then the gear calculation would also be sloppy. The key insight is that gears are discrete: there's a countable number of choices. So if I can extract the gear, I should see only a discrete set of results: plotting gear over time should show steps, with transitions between the steps corresponding to shifting, with deviations from the steps only when the rider is coasting with the cranks stationary, or, hopefully not often, spinning the cranks while coasting. The issue with this approach is it depends on both speed and cadence being of equal quality. ...

In the previous post I compared power from the Stages power meter to power from the Vector power meter (or meters, since L and R are separate) measured by DC Rainmaker on a ride he did in DC after the Vector release in Boulder, Colorado. Since Stages is measuring power only on one side of the bike, it is natural to compare the results with Vector, which measures power on each side of the bike separately. Before that, I showed that the Vector total power agreed well with Powertap and Quarq. If I assume that validates total power for the Vector, then it validates L and R power separately, since total power is derived from L and R power (the validation would be invalid if there were errors which naturally canceled between the L and R side, but I can't identify any). But Stages does one thing I really like: it measures cadence multiple times per second, instead of relying on an average cadence associated with the time for a full pedal rotation. The constant cadence approximation l...

The last time I compared DC Rainmaker's total power numbers from Vector, Powertap, and Quarq on a typical ride near DC ( Zip file here ). The result was excellent agreement by my standards, considering the meters are measuring different points in the power transmission path. That leaves the Stages , which he also used. The Stages is not a total power meter; it's a left-leg power meter. It produces a derived number for total power by doubling left-leg power, but if you even glance at any Vector data, you realize that left leg and right leg power differ. Vector is also not a total power meter: it's two power meters. It's a left-leg meter and it's a right leg meter. These are distinct and are calibrated separately. You can derive total power by adding the two together, and the assumption here is total power is the sum of the left leg power and the right leg power. This is an excellent assumption as long as I'm not pushing with my hand on the crank arm. So...