terrymorse 

They arrived last night:




My years of avoiding the power meter bandwagon has come to an end.

Not sure if this is going to be a good thing, or a bad thing.

It's just numbers, right? No need to become obsessive about some silly numbers.

Oh boy.

TMonk

Enjoy! I am considering joining the pedal squad, however I am looking at the Duo's. I have been (exclusively) a powertap hub user for the last 10 or so years.

On my (road) race bike I race on feel, so the advantages would be diminishing there. On my daily driver/training road bike I don't mind the heavy and unaero box rear wheel. What I really want is the ability to pace myself better in the Time Trial, which I've been getting more and more into the last few years (ITT and TTT).

ericcox

I have the duos. At current prices, I'd probably just get the uno. You trade a little accuracy for the price, but the reality is that while I do use the power data, both for training and pacing, I rarely look at the pedal dynamics other than to say, "huh - interesting." My left leg seems to be a little stronger than my right, but from all I've read, it's not enough to worry about. The uno will still provide consistent numbers, and as long as it is all you are using consistency is probably the most important thing.

I will also say I love the ability to switch easily between bikes. Just don't be like me and remember mid-ride that when you moved them from the gravel bike with 170mm cranks to the road bike with 172.5, you failed to reset the crank length on the head unit....

TMonk

ericcox good point about the Uno's, seems like better value, especially if the accuracy error in the Uno is a simple offset and not just a higher error bar on all readings. My anxiety is mostly around comparison to my Ptap hub, but if the Uno is consistent, then I should be able to re-calibrate my training based on the magnitude of the offset.

Still, I think of the Duo's as a "future proof" solution as well. As I get more into TT I realize how technical things can get. I will be working with a local coach on this soon, not sure if the dual read could ever become of value. Right now it's not really, nor has it ever been for me.

The Duo's price increase definitely reflects some diminishing returns IMO.

terrymorse 

So you're an old hand with power.

This is my first "toe into the water" at using a power meter, it's kind of intimidating. Not the setup, that was easy. It's what to do with the numbers.

RChung

If you're getting into TT, you'll probably eventually get into thinking about drag estimation. People used to ask me to help them with that. It didn't really take that long for me to ask, "what power meter are you using, and do you have a dedicated speed sensor?" because it became clear pretty quickly that if they had a single-sided power meter and were using GPS for speed that the data fidelity wasn't high enough to get usefully small variance in the estimates. Drag estimation, much more than training or pacing, requires high data quality.

I did almost all my protocol development with a Power Tap hub. It gives high data quality and has a built-in speed sensor. (And I could swap it between my road bike and my TT bike in 30 seconds).

RChung

Here's my advice to riders new to using power.

Snotrub

I'm dipping my toe in as well, after 25+ years of racing and riding. I fought it as long as I could, just like I did the 29" wheel.

ericcox

I mean, I did spring for the duo's myself (albeit before prices went up sometime last fall / winter) and am easily persuaded I'm wrong :-). One benefit of all these systems is you can add the second pedal later as well.

I am also not doing anything overly sophisticated such as drag estimations. Just an increasingly older dude who likes the numbers because they help me pace myself on long rides and have some sort of an idea of the kinds of efforts I can maintain in group rides and, it would seem based on my recent behavior, races.

RChung

Not everyone needs (or wants) to do the things I do, so not everyone needs the same degree of data fidelity. However, the key is to match your needs and expectations to what the device is capable of supplying. Many of us buy power meters in part because we hope to answer questions that can't be answered with speedometers, or wristwatches, or heart rate monitors. If our questions are simple, then simple devices will suffice. However, sometimes we wonder about harder, more subtle, more puzzling questions. In those cases you don't want to be asking the additional question, "I wonder whether my power meter is giving me reliable data?" If you don't ask those kinds of hard questions, you don't need nearly as much data fidelity.

terrymorse 

First impressions after my first ride with the power pedals:

1. It's a lot easier for me to maintain decent power on a climb than on the flat (or a slight downhill).
2. when I thought I was hammering in the flat, I wasn't.
3. Strava's power estimates are under-estimates.
4. Garmin 830 popped up a "performance good" screen during my ride. Thanks for that, but huh?
5. And "normalized power"? Come on. They're just making up terms.

RChung

Makes sense to me. The algorithm is based (mostly) on the Lp vector norm (where p=4).

ericcox

I've certainly started using the data in more sophisticated ways the longer I've had it. For those who are way more serious than I, the additional data is certainly helpful. I've done 2 races in the last 3 weeks and have enjoyed it (and not embarrassed myself). I could see getting more serious depending on how the summer goes and diving deeper into the data. I should add that I've only returned to serious riding for about a year, and am stronger now than I was 13 or so years ago when I was balancing small kids and limited riding time.

terrymorse 

Well when you put it that way, it's obvious!

guachi

From reverse engineering normalized power that I see in Strava, TrainingPeaks and other places it looks like the number derived is what constant power you'd need to output to equal the same training stress score.

Example: Ride at a constant 100% of FTP for one hour and 50% of FTP for one hour. Your training stress is 125. 100 from the 100% effort (1.00x1.00x100) and 25 from the 50% effort (0.50x0.50x100). Your average power for this ride is 75% of FTP. If you maintained a constant power and wanted to achieve a training stress of 125 you can reverse the formula. 125/2 hrs = 62.5 stress/hour. Divide by 100 = 0.625. Take the square root = 0.625^0.5 = 79.1% of FTP.

popeye

Well that sounds like fun.

RChung

That's the right idea, but not quite the right calculation. The "equivalent" steady state power in your example would be 85% of FTP and the training stress would be 146.

Also, Strava doesn't quite use NP; it uses a closely-related variant that's used in Golden Cheetah called xP.

Seattle Forrest

After a couple weeks of riding around with your new power meter and getting a feel for what the numbers mean and what 200 and 300 and ... watts feels like. You'll want to start looking at the "power curve" in Garmin Connect. If you use the web version it's down under the map, in a "tab" like laps, their segments, etc. I don't think you can see it per ride in the app? Strava probably has something like that too. How much power can you put out over different time periods. Just pay attention for a while. Eventually that info will help inform your training.

RChung

I think that's pretty important. I use power to calibrate RPE, and RPE to modulate power.

Yes. That's often quite helpful. I've been saying that some uses of power data are more dependent on accuracy (as opposed to merely "consistency") than others. Drag estimation is one of them. Estimating the "power curve" is another, because we're often interested not just in the average level of that curve but also the first derivative of that curve and its integral. (But, as I try to remember to point out, not everyone is interested in those things or what to do with them, so not everyone has the same data fidelity needs).

terrymorse 

Thanks. After my quickie test ride yesterday, a "Best Efforts Power Curve" did show up in Strava (Training > Power Curve).



Strava "Best Efforts Power Curve"

So I guess the basic idea there is to try to move the curve upwards over time?

I also see that Garmin Connect web page now shows VO2 Max and Functional Threshold Power values. Since I was just fooling around on the ride, I suppose those are just very rough estimates.

Much to learn.

Doomrider74

Sorry about the slight thread hijack but is there much difference between a single sided crank arm power meter and a single sided pedal-based system, in terms of accuracy of the data?

RChung

Not much, which is kind of interesting--pedals are a "noisier" platform, which is why pedal-based power meters took much longer to come to the market. The crank can also be noisy (especially the right crank) but pedal orientation matters, plus you have less room to work with.

That said, the added noise in a pedal system means that the "instantaneous" power readings from them can require more averaging even if they're close over a full revolution. You can sometimes see this in max 1 second readings. (This is why I don't pay much attention to max power unless I know what power meter it was measured on--and even then I don't pay a huge amount of attention).

[Edited to add:] There's a special case with some dual-sided instrumented cranks based on the Shimano with the spider made up from four asymmetric arms: they're known to be inaccurate, and inconsistently so.

Doomrider74

Thanks. I'll probably go for a single sided 4iiii 105 crank arm at some point.

Seattle Forrest

I want to bring the right side up on mine. Spend my time and deliberate effort improving my weaknesses.

I'm assuming Strava must have this: in Garmin, when you look at that (power curve) chart for a specific ride, they can draw it over another one summarizing your last month, year, or everything. That's a good way to see how today's effort fits into your historical strengths and weaknesses.

terrymorse 

Yes, here's a sample Strava power curve for today's ride and the best power curve (solid gray) for all of 2021.





If the "today" curve is along the top of the "best" (solid gray) curve, I guess that means today was equal or better than the best of 2021.