We only see that the power goes up and down and that the Stages graph is usually quite low, but I want you to have it available before removing all the small peaks which in the end are the most important ones when determining the accuracy of the power meter.
But more of the same, there's not much clarity to be able to see data clearly and show you what I want, so I'm going to go much further, and smooth out the graph to 5 minutes. Much better now, right?
Well, what you'll see here is that there are two graphics that line up almost perfectly, the PowerTap one and the bePRO pedal one. At the beginning there's a difference of about 7W between them, but the one that stands out is the Stages one, well below the other two.
This is where you begin to see the need to test with three or more power meters. Because imagine you were facing the PowerTap hub with the Stages crank. How do you know which one is measuring power correctly? And even more, why the difference in power? This is where the third unit comes into play, which is the one that allows you to give the whole perspective to the tests. As I said before, in this workout I was quite fatigued, with tired legs a trail of 2,m of accumulated unevenness was to blame.
Why this huge difference between the Stages meter and the other two? Easy, because of the way the three measure. The PowerTap measures the total power of both legs, the bePRO measures each leg separately and the Stages measures only the left leg and multiplies by two to give the total power.
Generally my power distribution is quite even, around , with the right leg predominating a little more, so after seeing the data I quickly went to see what the distribution was that day. Let's move on to a different day. First of all I want to show you the graphics without smoothing, so you can see why I like to upload the smooth images which is actually the same thing you do with your cycling computer when you select power at 30s, for example.
Impossible to appreciate anything, but that's how you'll see it when you sync your device with the platform you're using. However, I use it to see the peaks of each of the meters and to be able to judge their accuracy.
But let's go with smoothed graphics. At the beginning of the activity everything appears quite correct and aligned, at least until the stop that can be seen in the graph. Yes, the punctual power peaks are separated in some points, but it is totally normal because of what has been explained before. The trend followed by the three graphs is the same, with the reference and inflection points coinciding.
There are minimal deviations at any given time by any of them, but it does not present any problem in its use. It is from the stop when the deviations by the three potentiometers begin. And you can clearly see how they are deviations that increase over time.
None of the three measures in a totally wrong way to rule it out directly, because the trends are coincidental as well as the turning points. The graphs are parallel and when one goes up, the others do too. How do you know which of the three is giving the most accurate data? Impossible to know. But the variation and difference in power is increasing, in my opinion due to temperature changes and how they have affected each unit and its speed of adjustment to these changes. So in the next training the goal was to see how they react to the expansion of the materials produced by the temperature, because it's an output with a constant rise in which there is a permanent variation in temperature, dropping as I go up the port.
The rise in core temperature is not real, because at that time I was standing making different checks, but being in the sun the Edge is simply warming up for that reason.
As soon as I start walking again you'll see that the temperature drops again. The temperature variation is up to 10 degrees. In the initial part of the climb I had to do 2 minute intense intervals and 1 minute calm. Here things are pretty even or at least the same way we have been seeing in all previous tests, with bePRO and PowerTap correctly aligned and Stages slightly below in terms of power because of my personal power distribution, with predominance in the right leg.
After stopping in the village at the top of the harbour and waiting for the temperature change we can see more acute differences. I could have done a manual calibration of the potentiometers, but I remember that the idea is to test them under real conditions of use. Besides, I am sure that the most normal thing is not to stop to do manual calibrations, but that you as a user of a power meter will simply calibrate at the beginning of the route at most.
The PowerTap G3, as indicated above, performs constant calibration when you are not pedaling, so it should continuously adjust as the temperature changes. But if during the ascent everything matched quite correctly, it's on the way down that there are discrepancies. In this second part I want to forget about the Stages reading, because those higher peaks when the power goes down are not caused by the power meter, but by the unit that is recording data.
But I want you to look at some other details, not just the obvious one. If you look at the clip of the climb, bePRO and PowerTap are aligned almost perfectly, with Stages slightly below for measuring left leg power and multiplying the two.
After the stop we can see that now the curves that coincide are the Stages and PowerTap ones, being the bePRO graphic above, although little by little they are aligned again perfectly as I approach the end of the training.
There is no other explanation for this behavior than the speed each unit has in adjusting to temperature changes.
Or, how the temperature affects each unit. Again, I highlight one of the best aspects of the PowerTap G3: its constant self-calibration. So while the other two power meters need a few minutes to adjust both have automatic adjustment for temperature change , the PowerTap G3 is much faster to do so, because every time we stop pedaling, it recalibrates fully automatically.
If I had stopped at the end of the descent to make a manual calibration from the device, the power adjustment would have been faster in the other two units. And what about the cadence? Well, there's nothing to report. At no time have I been able to see any strange behaviour.
In the graphs you can see peaks above and below, but they are simply moments when I stopped pedalling and are the data received by the unit. For some reason PowerTap sends a peak to zero and bePRO a very high peak, but that doesn't affect the final average or, mainly, the cadence reading we have during training.
As you can see, all three devices detect the same cadence data, even though the PowerTap G3 can only estimate the number of pedals per minute.
The PowerTap G3 has become one of the reference power meters in recent years. It is easy to understand why: very simple to use, no incompatibilities in its installation and the data obtained is totally reliable. What you have to decide is if you are interested in having the power meter on one wheel. It will depend on whether you use one wheel for everything racing, training, climbing, etc , or on the contrary you have your training wheel set and on competition days you use something special depending on the type of event you participate in.
It also depends a lot on the type of competitions you attend, since short races where you ride a wheel and respond to attacks the power data will not have much weight when deciding whether to respond to that attack, but for longer events it can become a must.
If you only use one set of wheels you won't find any simpler, more reliable and cheaper option. Put a PowerTap hub in your life and forget about everything else. But if you use several sets of wheels then you must decide whether to buy several units for the different games or decide which one you want to have the power information on. It is one of the most economical options when it comes to measuring power, and it does so in a precise way. Post 6 of 15 views. I would agree with "poorly".
Post 7 of 15 views. R10C wrote:. Post 8 of 15 views. Put the magnet kit on and get accurate cadence and speed. Team Zoot So Cal. Post 9 of 15 views. Karl wrote:. Post 10 of 15 views. I hope speed is accurate Post 11 of 15 views. Post 12 of 15 views.
It's an estimate, but it really doesn't matter. Long story short, don't worry about cadence. Post 13 of 15 views. Within our walls we also build PowerTap power meters. Since the early s, PowerTap has been part of the Saris tribe , helping push athletes towards peak performance. The special sauce of riding with power comes from the fact that unlike speed or cadence, power is not affected by hills, wind, terrain or other environmental factors.
The legendary PowerTap hub-based system was one of the few to open the doors of power training to everyday riders. The popularity of virtual training apps, like Zwift and Rouvy , have a lot to do with this. Power output is part of the experience, enough so that even without a power meter or smart trainer , their algorithms are able to calculate power based on the bike trainer being used or the speed of the rider. This interest in power training has been on the incline since PowerTap first came on the scene in , with more manufacturers and types of power meters available now than ever.
Yet, one constant remains — the fact that power is the most accurate and reliable way to measure cycling intensity. My point was that training cadence should match racing cadence or vice versa when possible. I'm not counting noodling along at low power, etc. There are exceptions. I also think terrain should only be taken into account when your gearing no longer lets you spin at your desired cadence. The only difference is the gear you are in and how quickly the ground is moving underneath you.
Well, the reason why we train with power rather than by speed only, or by cadence only, is exactly because the latter depend on terrain and power. And the moral of QA isn't that you need to exactly mimic average race cadence in training -- do you also mimic average race pedal force in training?
Race Reports! Updated posts. My threads. My favorite threads. General Discussion Triathlon Talk » Powertap virtual cadence and speed? Rss Feed. Moderators: k9car , alicefoeller Reply. Subject: Powertap virtual cadence and speed? I just read that the G3 powertap provides virtual cadence and speed as well. Did you Powertap users take of the speed cadence sensor once you put the Powertap on? My Race Log. Jason N. Subject: RE: Powertap virtual cadence and speed?
The speed is pretty much spot on I don't really pay that much attention to cadence anyway though. I'm sure that it can probably infer the data, but if you can have the actual numbers, may as well use them. Here are the cadence traces from the same ride: Notice that when the cadence on the SRM or Polar is steady then the PT's cadence is mostly steady but with occasional blips, and when the SRM or Polar's cadence is variable, the PT's cadence is also variable but with occasional blips.
All that said, cadence doesn't much matter anyway.
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