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

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. ...

Last time I proposed an algorithm for pedal smoothness. I can hardly take credit for it, it was basically the reciprical of Coggan's variability index without the 30-second smoothing. It's fairly obvious to apply it to the pedal stroke, as well. Here's some data left over from the old Metrigear Vector blog, showing measurements taken with the Metrigear-era Speedplay Vectors. These data are at a much higher sampling rate than would be recorded by an Edge computer: they show the detailed power and cadence during just a few seconds of a longer "ride" (on the trainer): I used Plot Digitizer to pull points off the plot (off-topic: I really like Plot Digitizer; it's replacing g3data , which I previously used). Here's a view of a subset of those data. Curiously, the left leg is going negative power, while the right leg does not. The plot also shows total power, the sum of the L and R legs. This shows a strong oscillatory character: it goes from a ma...

In anticipation of the release of the Garmin Vector, or perhaps the Rotor Flow, Garmin added a pedalstroke quality field to its Edge-series head units in the recent firmware update. But consistent with the Vector-team's approach to not release anything which they won't stand behind, on the first public release of the Vector power meter, that field remains unpopulated. It's an interesting question about how important pedal technique actually is. I think most cyclists think if they can pedal in a smoother, more uniform fashion, their cycling will improve. This has been difficult to demonstrate in the laboratory, however. For example, a recent work by Arkesteijn, et al, used force-feedback to encourage riders to pull up more on the upstroke. This worked, improving the uniformity of force application around the pedal stroke, but gross energy efficiency of their cycling failed to improve. On the other hand, it appeared the smoother pedaling increased the ability of the c...

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...

DC Rainmaker has posted another dataset to his blog ( Zip file here ). His early installation issues behind him, these data serve as a valuable comparison between the power meters he's using: the spanking new Garmin Vector, the Quarq Elsa, Powertap, and Stages. The point of this post is to quantitatively compare the powers. But first some discussion... Each of these power meters is measuring power at a different point in the transmission path. Vector gets first shot at it, picking up power transmitted through the pedal axle. Stages is next, measuring power in the left crank arm. Next, Quarq measures it in the crank spider. Finally Powertap picks up the power which manages to make it to the rear hub. The largest losses are expected between the Quarq and hub, as mechanical losses in the chain and in the rear derailleur pulleys converts mechanical power into heat before the Powertap sees it. Between the Vector and the Quarq, it takes more imagination. Brim Brothers, not yet...

Garmin Vector vs Quarq Elsa: L-R balance comparison The Garmin Vector is clearly the most anticipated power meter to come onto the market. There's a few reasons for this. One is the freedom of choice it affords in selecting components. With a Powertap, you need essentually a new Powertap for every wheel. With crank-based systems, restrictions are more limtited, but swapping pedals is generally considered easier than swapping cranks (this is debatable, however: my Lightning crank is super-easy to take off and on). But perhaps more than this is the ability to measure independently the left and right pedal. This is power measurement at essentially the point of contact. It's directly measuring the forces applied by the rider. That was the inspiration for the name: "Vector". It's measuring the force vector applied by the rider's feet. This is somewhat of an academic point in comparison to the crank spider, since it's generally considered to be the ...

It's a general principle in cycling that riders, or teams, shouldn't be punished for riding faster. Cycling's a fairly simple sport: faster = better. Or at least it has been until the 2013 Tour of Poland. Today's stage was the first one where it really rose to people's attention. Here's the CyclingNews results . The "attractivity" ranking is the sum of points for intermediate sprints and KOM points. Riders are ranked on these points, with first place getting a 30 second deduction, second place a 20 second deduction, and third a 10 second deduction from overall time. Ties are resolved optimistically: if two riders tie for first, they each get 30 seconds, they don't share the points for 1st and 2nd (which would be 25 seconds each), which would make more sense. But that aside, the use of the daily ranking to assign points makes for some non-obvious strategies. Consider the case where rider A ahead in GC. Rider B is 29 seconds down on GC. Ri...