Presumably you bought a single-sided power meter believing that consistency is the only thing that matters, not accuracy. How do you like them apples now?

Hahaha. Quoted for the next 10 years of people saying, “as long as the number is same all the time who cares if it’s correct”.

Uh, i bought the single leg because I didnt have much $ at the time, still dont, I traded liquor for the quarq... but i do like consistency and stuff

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Professional Triathlete and Professional Orchestral Musician. Bikes, Bass, Beer.

Do you do a zero offset before every ride on both pm’s?

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Yep. Make sure to do it multiple times

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Professional Triathlete and Professional Orchestral Musician. Bikes, Bass, Beer.

^^This is great

I still have the single leg Stages that I bought in the summer of 2014 - First Gen. I was running a 2nd Gen Dura Ace Stages the past two years on my race bike and noticed the power to be between 10-20 watts lower than my old Stages. I calibrated both before every ride. Basically it just comes down to them being different systems. One might read a bit high or a bit low but what's important is that they are consistent.

Kind of a pain in the ass, but I would do testing on both bikes. My old Stages is on my trainer bike, so I would have indoor power numbers on that and outdoor on my DA Stages. I will have one of the new Quarq dZeros on my race bike this year so we will see how much of a difference there is.

Thats what I kinda figured. Just test and get a sense between the two

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Professional Triathlete and Professional Orchestral Musician. Bikes, Bass, Beer.

Can these be calibrated like the PowerTaps? You get a chain and weight for which you have an accurate total weight, and hang them from the pedal. My PTs give really consistent result across my fleet.

It’s one sided so I don’t necessarily think that is the best option.

If it’s off because he uses more power on his left leg. It’ll be even more jacked up trying to compare power to a 2 sided.

Well think about it this way. I don't know how left/right balances ranges tend to be, but at 300 watts of true power output, if your legs are 45/55 then you'll get a reading of 270 on the pioneer. Doesn't seem too unrealistic of a scenario to me.

Well shit, didnt think about it like that. Seems to make sense. I just count to 4 usually think about percentages is tough

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Professional Triathlete and Professional Orchestral Musician. Bikes, Bass, Beer.

No need to quote. The joke is years-old now.

Do a "stomp test" on the Quarq using the Qalvin app and an ANT+ dongle. Search the web for info on how to do this. That way you'll know if the Quarq has the proper torque slope calibration.

I don't know if it's possible to check/modify that on the Pioneer.

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Thanks for the tip. Will do

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Professional Triathlete and Professional Orchestral Musician. Bikes, Bass, Beer.

Why does this:
always seem to be come right before this:

The "exactly to this very day 1 year" means that there were still PT GS hubs available at that time for $299.

Because both are true?

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Professional Triathlete and Professional Orchestral Musician. Bikes, Bass, Beer.

So, if I understand your post properly, the Quarq said you did the same ride on 2 different days with a perceived effort control. On ride 1, your Pioneer showed your left leg averaged 136 watts (272 = 136x2) and on ride 2, your Quarq showed a 300 watt average.

Without an independent and known control, there is no way to know which, if either is "right". And it's possible they both are.

Pretty much. Now I'm realizing this folly of my ways

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Professional Triathlete and Professional Orchestral Musician. Bikes, Bass, Beer.

If you have a friend with a powertap wheel or a two sided pedal power meter that you can borrow you can compare against a third number. Still not a guarantee it'll confirm one or the other but my money is on it matching the Quarq.

You can check the calibration of a Powertap's "slope" but you cannot recalibrate it.

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You mean like checking the torque slope of the Quarq, as mentioned above, right?

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Tom A. wrote:

I don't know if it's possible to check/modify that on the Pioneer.

There is no mention of being able to check let alone set slope in the Pioneer manual.
http://pioneer-cyclesports.com/us-en/support/products/manual/SGY-PM910v_usersmanual.pdf


It does have a function that will display radial and tangential forces in Newtons when doing a zero offset, so that option could be used for validation purposes, or at least tested to see if the tangential forces make sense when compared with a known load.

Pioneer's own head unit allows you to apply a factor to power data. But that's not available if you choose to use another head unit, e.g. a Garmin.

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Truman: "I don't give them Hell. I just tell the truth and they think it's Hell."

I was away from my computer for a bit before I hit the <post> button, si I missed that reply. Yep, that would tell you if the Quarq was accurate.

To play devils advocate with my N=1, I replaced my stages with P1 pedals. Until recently I have been riding with both to compare them. They have been remarkably consistent with each-other when comparing interval averages. I was hoping upgrading to dual power would add 10 watts to my FTP, but looks like I need to find that 10 watts the old fashioned way :)

I do believe having dual or total power is preferable, and it was a part of the reason I upgraded. I do not believe it is a game changer though. I have a hard time seeing what the OP missed out on his or her training by having the Pioneer read 30 watts lower at effort.

The answer is...wait for it... it depends. I currently have a 4iii (left side), 2 Powertap G3s, 1 Powertap GS, and a Power2Max that will be installed next week. I have had 3 Stages units in the past. What I learned from comparing my first Stages with my first G3 was that while average power tracked closely over varied 60-90 minute workouts, the total power from the Stages varied by 40 watts or more from the Powertap depending on the effort. For low cadence (<60) cadence (, high power efforts, the Stages would read higher than the G3. For high cadence (>110) low power efforts, the G3 would read higher. This tells me that my left/right leg balance changes depending on the effort.

If I were to use a 1 sided power meter for my workouts, what I would lose is there ability to accurately match the total power specified at both low and high cadence efforts. If one believes that this is important, then one loses the ability to get maximal results from one's training. But, in my case, I don't lose the ability to pace a TT or hillclimb with a one-sided pwoermeter. But these result apply only to me. Others may or may not get different results. Testing is required.

Hopefully this made some sense.

The P1s will give you your left/right balance. So if that is close to 50/50, and the numbers from the P1s and the Stages line up, there's a pretty good chance they're both mostly accurate. If your balance is off on the other hand, and the numbers still line up, you know something's off.

And to those of you that say, "Meh, my balance is good. I don't want to spend the extra money", I say that my balance is 48/52 on most rides. That sounds pretty good, right? Until you realize that if I push 100W total, a left-only PM is going to register 48W and report a total of 96W. Which is 4% off the real value. Which is more than the advertized accuracy of most PMs.

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Citizen of the world, former drunkard. Resident Traumatic Brain Injury advocate.

Besides that, I don't think it's a matter of you trying...

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http://bikeblather.blogspot.com/

Good point.

While it is a very good start and I certainly recommend people do the slope check if they can, knowing a power meter's slope is valid is a necessary but insufficient condition for ascertaining power meter accuracy.

There are a range of other factors to consider, and much also depends on what one means by "accuracy".

Accuracy under what scenarios or conditions of use? e.g. accuracy for quasi steady state over longer duration vs short duration when sprinting maximally, accuracy when starting or stopping pedalling, accuracy of crank velocity measurement, and so on.

Whether these various factors matter comes down to what applications you intend to use the data for.

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Thanks for the reply Jan, I am quoting you and your example, but also responding to the discussion in general. I understand how the balance effects the power calculation. Your example of 4 watts is not much (I cannot feel the difference between 96 watts and 100 watts), but up that to a 300 watt example and all of a sudden it is a meaningful difference. I understand that.

What I don't fully understand is what actionable information it provides. You can make a strong argument based on someone's LR balance changing at different intensities, different cadences, different levels of fatigue, etc. If an individual's LR balance is not consistent, then a single sided power meter will loose consistency across different conditions. Again I understand that limitation.

With those points understood, how big of a difference does this make? With reasonable LR balance, and understanding that balance changes, we are not talking huge variances in balance changes and huge variances in single sided measurement error contributing to large swings in consistency. I do not think many people are pedaling with 45/55 one day, and 55/45 the next. Perhaps I am wrong there. My point is not that it does not matter at all, my point is that is does not matter a ton. When we are talking about buying a $300 stages vs. $1,000 pedals there is a value judgement to be made there.

WRT to the the original comment I responded to objecting to the notion that consistency is all that matters, I still do not see why accuracy is treated at such a premium. Yes, if you are comparing one power meter to another, sure accuracy is important. Outside of that, if the meter is consistent, what are you loosing? Unless your meter is wildly inaccurate, I think the training effect is going to be the same.

As AlexS said in the post above yours, it depends on the application. If all you want is essentially a TSS meter for a single bike, then sure a single sided meter might fit your needs. If your needs are more demanding then you start having to look elsewhere.

In point of fact, they very well may be, if not due to fatigue, then due to differences in absolute intensity or cadence, and if not on average, then at a minimum moment to moment.

The bottom line is that the only way to know your total power is to measure your total power. Measuring the power of only your left leg and then doubling it is a guess that under most conditions is essentially no more accurate than, e.g., measuring your heart rate (in which case, you might as well just buy a heart rate monitor, as they are cheaper).

That is a very interesting point of view. Please don’t get wrong in questiong your expertise, because I don’t. But I ride 4 to 6 times a week on Trainerroad with dual sided PM. 2 to 3 times at serious efforts, but I never have more the 2% difference between left and right. And most of the time it hoovers around 49-51 to 51-49 %. Are you saying I’m an outlier and larger differences are more common or to be expected?

Thanks,

Jeroen

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Owner at TRIPRO, The Netherlands

I can vary L/R from 55/45 to 48/52, but mostly from 55/45 to 50/50. Depends almost entirely on power output. just cruising along at 70-75% or less will be 55/45. the closer i get to race effort, 90-95% contribution balances out to almost 50/50. over 100% is when I start seeing power skew to the right leg 49/51 type numbers.

That is very interesting. I am pretty similar. Zone 3 I am ~46/54, Zone 4 ~49/51, Zone 5 ~46/54. My right leg is dominant in general and is a bit stronger, but the balance seems to go with focus. Below Zone 3 and I just don't focus on technique because I am cruising. Zone 4 requires my attention and I tend to concentrate on my technique and stroke. Zone 5+ I am just hanging on and focusing on technique and stroke becomes impossible.

Which power meter do you have?

I have some data files from one guy who had both a Stages and a PT on his bike. If you use the difference between the Stages and the PT as an estimator of his L/R balance, you can see that for him, the difference depended on whether he was climbing or riding steady or doing intervals, or at low or high power, or (especially) at low vs. high cadence. I don't think I have any indoor trainer files for him so I don't know what his putative L/R balance would have looked like in that situation but since indoor rides *tend* to be a little steadier than outdoor rides, I could be convinced to expect less variability in his L/R balance.

I have P1, but I loaned these to a friend but also have a Pioneer and the Garmin Vector 3. I will set all of them on the bike and what happens under load differences again. Unfortunate over here we can only ride indoors for now since the wether isn’t really attractive to ride outdoors and mountains we don’t have at all. I live in about the flattest country in the world so no real climbing ;-)

Thanks anyway,

Jeroen

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Owner at TRIPRO, The Netherlands

You could always upgrade your Pioneer to a dual-sided version. Then your power numbers would probably be pretty close to your Quarq. As others have mentioned, your left/right leg imbalance is probably causing the power number differential between the two powermeters.