shovelhd

If you have two identical power meters and both are calibrated then of course you can compare data and expect tight accuracy.

island rider

SRM always seemed to me to be a Cadillac solution to a Chrysler problem, especially since I already use Garmin as a head unit. But I guess we should talk as I start thinking about buying and replacing bikes.

So... you would test the meter by say hanging weight from the crank and then what? Or do I need to reach out to Quarq and ask them about the reading?

EDIT - BTW, I was reading up on Quarq's site about calibration on Garmin's. I like your explanation.

gsteinb

I can only speak for the SRM process

You take the zero offset both weighted and unweighted four times on each side and punch the numbers into a spreadsheet with a formula. It spits out a slope.

shovelhd

Ok, so now you have the measured slope, is there a facility in the PC6/7 to adjust it? I can't remember if it shows up on the Garmin.

gsteinb

yes, you can manually change the slope in the head. You can physically change it in the powermeter itself using a garmin.

Alaska Mike

The Quarq calibration process involves a known weight hung from a crankarm, the Qalvin application installed on a smartphone or computer, and an ANT+ dongle. The Qalvin application also provides a few diagnostic functions as well. I looked into it, but haven't gone that route just yet. I might be sending in my S975 this winter, just to see how it's holding up. It's been perfectly fine and stable so far, but I figure it can't hurt to check. I haven't been exactly gentle with it, and it's been submerged before, in addition to a lot of washing and wet rides.

island rider

That seems unlikely for me. I wonder if that's something a dealer would do for me locally.

tetonrider

they need not be identical meters. (by identical i assume you mean same make & model.) that's why an accurate meter matters. doesn't matter what brand or model it is--if it is an accurate device and someone can calibrate it (and check it periodically), then the data will be good.

not everyone cares equally about data quality, though.

glad you found it helpful.

as for "chrysler problems"... in my experience and from what i observe in others, there are some people who place a great deal of trust in the numbers. they train hard for years. if they have a test where their meter reads low, it can hurt them psychologically...much less months and years of data that is slightly off, only to be discovered when they switch to a different device.

this isn't everyone, but there are LOTS of people who invest a great deal of time and mental energy into their training (with power).

some don't worry much about it. i do know people who have purchased $3000 power meters which are essentially just bike computers. they don't care. but others do care more deeply. there's no absolute right answer.

my issue is that some of the people who will care in the future don't realize that choices they make now will cause them problems in the future.

it can be even simpler. when you're dead-on with your method you really only need two measurements per side (just to see if there is any difference between big ring & small ring for each side). the more measurements the more one can verify how good their process is. if one is doing 4 measurements per side and sees a wide distribution, something's wrong with the technique.

in any event, when one has done it a few times and owns a suitable mass for the calibration, it takes about 5 minutes. i like to check calibration every 6-12 months. it basically never changes for my devices, but i think of it as an early warning indicator.


i am hopeful the pc8 might include it, but so far only the 800 seems to update my units. it *should* work with the 500 for me but never does. maybe the 510/810/1000 can do it; i haven't tried.

possibly. i service quarqs for friends and customers. i happen to have the wahoo key. all that application does is walk someone through the manual steps gsteinb described above.

again, takes about 5 minutes if someone has the tools.

one can do it with just a garmin.

island rider

I train pretty heavily with the numbers. I'm not as invoked as others, but my real concern is that the numbers are repeatable and consistent. It don't care that my FTP is actually 600 rather than 625 or whatever, just that I have zones I can use on a consistent basis. If they are different between different meters that's a problem.

I'm straight up confused and concerned now.

Ygduf

quality can mean different things to different people. Some chefs go by taste, some measure by the gram.

I'm not building a spaceship, I don't need power measurements to be air-tight.

gsteinb

That's true, but let's say you're a guy who has a strength at shorter efforts. And let's say that a specific meter, while generally good, has a weakness at accuracy between higher numbers. If you're doing a lot of short hard efforts and the data isn't consistent that could be a pretty big issue. It could make it pretty difficult to track what you're actually doing. That might not mean a heck of a lot on a 5 hour group ride…who cares if your 1 minute was 700 instead of 725. But if you're doing multiples of those and tracking them over time if there isn't accuracy or consistency you might as well save the cash and go back to PE and a stop watch.

tetonrider

no, but pretty much by definition none of us need power.

athletes have different needs and desires. gsteinb's post illustrates this quite nicely. what's right for someone is not wrong for another.

my own bias is that if i'm going to bother to record it (or if a trainee is), i'd like for it to be as accurate as possible. a key reason for me is that if data resolution or accuracy is not there at the start, one will never get it back if later one realizes s/he needs it. sometimes it is not always possible to predict future needs, so i take a conservative approach. i've been burned when i haven't.

reminds me a little of a debate when mp3s were first coming into popular use. 128kbps was "good enough" for most; "but higher rez takes up too much space" was often heard. i argued for (and opted for) lossless compression or no compression at all. similar thing with digital imagery, saving only JPEGs, etc.

each to his own, of course. i hope people make informed decisions before sacrificing accuracy. hard for one starting out with power to know what they don't know.

globecanvas

Yeah, I think my FTP is around 725w, but if it's as low as 700 I don't really care.

tetonrider

heheh. iff he's 600 or 625w @ threshold, then, yeah, he doesn't need to worry about it -- someone else will handle the details.

Alaska Mike

Island Rider-
What everyone is saying is this: If you have one power meter, it really doesn't matter as long as it's consistent. It could be measuring output in squirrel eyeballs or whatever. If you're comparing your numbers to anyone else's, you're missing the point. Stable, repeatable training data is what is important.

My Quarqs are very consistent with each other. My Stages seems very consistent with itself, although there are some differences with the Quarqs. I understand there are differences with Power Taps/SRMs/whatevers as well, to varying degrees. You pick your standard and go with it.

I've been fairly impressed with how Stages has tried to improve and mature their product since it's been introduced. It's easy to move between bikes, and has so far been pretty reliable for me. I'm fairly imbalanced left/right, with my right leg producing a fair amount of power more than my left. Your difference might be less pronounced, but if it's your only power meter, does it really matter? You'll have a baseline, based on a standard, to build your training plan off of. If you're smart, you'll use the power meter in a structured manner, and not as an eWang to impress your friends. It's as pointless as comparing maximum heart rates. It's a means to an end, not the end itself.

***Note: This is coming from a guy who has started to top out on what power he will likely ever be able to make, and it isn't all that impressive. The best thing I can do now is lose a quarter of my body weight to get my W/kg to anything approaching competitive. I should have spent the money on Liposuction...

island rider

Sorry, it said FTP, I meant top sprint speed. Damn autocorrect.

island rider

No, the point for me is that if Quarq A registers 150 at a given effort level and Quarq B registers 180, that meaningful when it comes to training and switching between those two bikes. I don't care that my 5000 watt sprint is actually a 4900 watt sprint and not exactly the same "real power" as your 5000 watt sprint.

(I like to to low ball everything so Globe doesn't think I'm a threat.)

Alaska Mike

Then add 30 (or 1000). If it's consistent and repeatable in that power range, it's a matter of math.

In a sprint (or a 15sec-2min effort), if I'm able to comprehend any numbers I'm obviously doing it wrong. Any analysis happens later next to my computer in my pink bunny slippers. Then I have no problem doing the math, and while that 30W might make difference in the overall IF, those sorts of efforts are about putting it all in there, not meeting a certain wattage range. Even on the Quarqs, they can vary significantly. Some days I have it, so days I don't. I burn what I have for that particular duration.

That said, for longer intervals and steady state type stuff, the Stages is fairly close to the Quarq. From my unscientific observations, the differences are mostly academic.

Now, my intended use of the Stages is for rainy rides (we have a fair number of them), early spring rides when the roads are covered in sand and other debris, and cyclocross. Essentially, I use it when conditions are hard on drivetrains. When conditions are like that, in the interest of self preservation my out-of-the-saddle sprints are few and far between (with the exception of 'cross). Since all of my cranksets are SRAM Rival/Force/Red with the same length crank arms, I can swap from the 'cross bike to the commuter to the TT bike with a single allen wrench (2 if I have to swap a pedal). When the roads and conditions improve, I go back to the Quarqs.

If you are one of those that rides primarily when the sun shines, you might not see the need. If I don't ride when it's wet or otherwise imperfect, my season is down to a handful of months a year. For me, it's worth it.

tetonrider

FWIW, i'm not saying this.

how many quarq "1-meter owners" have only had just one unit?

seriously...regardless of brand there are warranty replacements, upgrades or model changes (with the manufacturer), or switches to another brand down the road. doesn't matter if it is PT, SRM, quarq, iBike or whatever else one chooses. today's data will inevitably be compared to data in the future--tomorrow could be the day one gets that new unit from warranty, and if either the new or old one (or both) is (are) not accurate, then there are problems.

if we add in another meter on a 2nd bike, it simply makes it more likely for one to notice a discrepancy faster.

again, everyone decides what is important to them, but the notion that a meter only needs to be consistent to itself because a person will only have one meter is -- in my opinion -- a bit short-sighted.

Ygduf

You're right, and let me tell you, it's absolutely not worth arguing any further.

tetonrider

since power varies with force and cadence, it's never really that simple. all else equal, wouldn't you rather have a device that could be calibrated by the end-user so you didn't have to do this stuff during an interval or at the computer?

your point is a good one: all you can do is all you can do.

i've lived with inaccurate meters before and have seen it for trainees. (i also find that when a meter is inaccurate it is often inconsistent, too--but sometimes this is only evident when doing very controlled testing, which is annoying/time-consuming.) i have observed that often times "not having it" can be influenced by what the numbers tell us. in other words, we see low numbers and assume we didn't have it (or high numbers and that tells us we did have it that day). as a result, if the numbers are inaccurate, a bunch of a cyclist's self-worth can be influenced by these numbers.

a personal example: years ago i was playing around with a head unit that required me to set slope manually. i switched to a different bike/different meter but had the old slope stored in it. went out for a 2 or 3' interval session. i was going all out, but my power was 30-50W lower than i expected. i'd been training super hard. i was a few intervals in -- just like always, i was completely spent after each one, but a few intervals in and noticing the low #s , i felt like $hit. i thought i should sell my bike. i questioned all the time i'd put in to training.

i decided to plug away anyway--if it feels hard it is still good work, i reasoned. got home and a few hours later realized what was wrong. the software i was using allows me to change slope after the fact and....i had been exceeding my targets.

30-50W for a 2' interval could be a season's worth of improvement. the story sounds crazy (who would feel this way about some intervals?), but i actually know many people who do use the #s to evaluate their progress....people who spend lots of hours on the bike and necessarily have some of their identity wrapped up in it. some may have given up on the session. we can argue whether that is ridiculous, but it is not that unusual for a racer to have a bad training session/interval/race/group ride/whatever and question things.

in this instance, my meter wasn't inaccurate, but i have had meters that were inconsistent. power meter data can and does affect training and moods. maybe not for you or for some other posters here, but for others it does.

but that's where the "good enough" thing comes into play. what's good enough for me might not meet the threshold for someone else.

good thing we have meters with various pros and cons at different price points.

agree. stages (IME) is worst at shorter efforts, particularly where power and/or cadence varies. MTB is a good example. as intervals get longer, there is less difference. the interesting thing i observe is many people i know (just personal, n=1 type of stuff) that are looking to stages are the ones who want it for scenarios that are sub-optimal.

seems a shame that you can't rely on your pricier (retail) meter to be MORE reliable in tough conditions. i agree that quarqs tend to be vulnerable in tough conditions (ask someone who has had their MTB meter!), but to me a higher priced meter should have a higher bar here.

i use an SRM on my cross bike, partly because i just move it over from my TT bike (with a ring change) but also because it is specifically designed to take a beating.

i think the discussion is a good one. like we said in earlier posts, there is no "right" answer. knowledge of the trade-offs prior to a purchase is important. maybe the discussion will help someone.

Alaska Mike

And yet, here I go...
If they don't re-test and adjust their ranges based on the new data when they switch standards, they're wrong. I'm sure the Team Sky kids did exactly that when they started their relationship with Stages. I'm sure Omega Pharma did the same with Quarq. When you're talking about measuring something as variable as human performance, periodic re-testing (even without switching standards) is a good idea.

If it's stable and repeatable, it can be compared across platforms.

tetonrider

of course...but it doesn't mean it is right.

try having a conversation with a friend or trainee who is used to doing an FTP test at, say, 300W and now sees 285 when they switch to a new meter. i've seen this before (and the new meter was indeed more accurate--their old one had issues). sure it's minor in the grand scheme of things, but psychologically it is very difficult for someone to let go of old numbers and zones, particularly when they are around a breakpoint.

if we were all robots and completely detached from the meaning of the #s , i agree with you 100%. since we're humans and have emotional connection with the numbers (natural when people spend 10, 15, 20h/week riding and staring at them), in practice it's not just a matter of saying "oh well, my XYZ meter just reads low. that FTP test that is 15W lower than i saw 6 weeks ago is totally cool."

human performance does vary. it's unlikely for anyone to argue -- all else equal -- that they'd rather NOT have an accurate AND consistent meter. an inaccurate meter just compounds a problem.

i suspect we agree more than disagree. i just can't ignore the human element.

Alaska Mike

Actually, I've abused my S975 Quarq quite a bit. At this point, having the ability to change cranksets with the Stages, to include chainring sizes, without a recalibration is quite nice. I may lose a bit of accuracy for the convenience, but the trade-off is less wear and tear on my primary power meters and the bikes they are used on.

I'd love an SRM, but have never run across one for what I'd consider a decent price. Some of that has been timing, and a limited local market for such devices.

Ygduf

ITT: someone is a dealer and will offer to sell you one