What do you mean by "using Strava?" Are you referring to the power estimates that Strava generates based on its known data (speed, grade and weight)? Or are you referring to actual power nums that get uploaded to Strava from your device? (I.e. is there a little lightning bolt icon next to your posted watts?) If the former, I'd encourage you not to place any stock in those estimates. If the latter, obviously that's an issue with either your meter or your legs.

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"Simplify, simplify, simplify!" -H.D. Thoreau

Actually, using a Quarq Power Meter with a 310xt Head Unit, I get different power numbers all the time in Strava. Strava will always have my power numbers lower than what the Garmin unit reads or what Garmin Connect says. My advice to the OP is disregard any power data you see in Strava.

TT for 48mi on a road bike at 25-26mph?
Was it all down hill?

Seriously. Humblebrag much? How is that relevant to your question?

I think Strava uses Avg P, not Norm P.
Which for a straight hillclimb KOM shouldn't matter, but for anything rolling, flat, etc it makes a fairly large difference.

The estimated "power" in Strava is for entertainment purposes only.

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float , hammer , and jog

Did you enter your weight in the profile area?

Exactly, per my friends who work there.

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clm
Nashville, TN
https://twitter.com/ironclm | http://ironclm.typepad.com

First to the OP, as everyone else has said, ignore the estimated power in Strava. I'm sure it can be occasionally close under the right conditions, but it is more often than not wildly inaccurate.



I'd also take the power metrics reported by GC with a healthy degree of skepticism. Obviously, the AP can vary a lot depending on whether you've included 0s or not, but for newer devices with the power metrics, the NP (and corresponding IF/TSS) have always been way higher for me than those that are calculated by any other source.

My metrics as calculated by WKO+ and GoldenCheetah always correspond closely, however the same ride data as reported on GC will show tangibly higher power and therefore I definitely don't recommend using it as a the sole source of your data.

Perhaps you should weigh yourself, and your bike. You may be putting in your aspirational weight, rather than your actual weight ;)

My strava climbs with my powertap are like 20w higher than the climbs that strava just estimates. Although, strava power comes out much higher on the downhills than I get on the PT. I guess I'm more aerodynamic than their algorithm thinks.

Damn, so I'm not as strong as I always thought! Crappy! I need to get on this WKO+...

Well actually, based off of what you said, you should be fine. You said you use a 310xt for your head unit, which did not receive the firmware update to calculate NP/IF/TSS. Garmin Connect only displays these metrics if your device calculates them, so if you have a 310xt, you shouldn't see NP/TSS/IF reported on GC.

So I would expect that the only number you have reported on GC is your AP (average power), which again can be skewed high if you are dropping zeros from the calculation, but I think other than that should be consistent.

Or at least, all this is based off of my experiences. I have a Edge 800 which calculates / shows NP/TSS/IF all that stuff in GC, and my 310xt does not.

Threadjack but that's ok.

Sorry, to be clearer, I don't have a power meter. I put the TT info in there to show my max power output sustained. Basically Flat course, out and back, little to no wind. (HR at 176bpm the whole way, suffer fest)

Weight, 135lbs

I was just wondering how wildly inaccurate Strava Estimated power was?

It's probably calculating your power assuming your cda is that of a standard road bike with standard rider. Since you are on a TT bike, that is going to make it wildly inaccurate.

that has been my experience with the TT. the slower I go, the lower the strava estimate is compared to my actual. the faster I go (like, downhill), the crazy high it gets relative to my actual.

Sorry - to be clearer

not on a TT bike, doing a TT with regular road bike, no aero equipment

How far off has Strava been for people? Estimated vs instrumented power output?

To be honest, I'm not sure because I don't know of a really easy way to compare a strava estimated power versus an actual power. Once you upload a ride with actual power, it overrides the strava estimate and I think it pretty much just goes away.

My basis for saying it's wildly inaccurate was based off of accidently uploading some old rides from a few years ago from when I didn't have a power meter. Strava listed these rides all as my PRs for best 5/10/etc min power and came up with these ridiculous numbers, like 300W+ AP for rides.

While 300W may not be a lot for some of you, I started riding in 2009 (when these rides were from) and am exponentially stronger now than I was then, so I can say with a pretty high degree of confidence that I have a pretty low degree of confidence in Strava's power estimations.

I can understand the appeal of wanting to be able to use Strava to estimate power, but even under very specific conditions that’s just a foolish pursuit. Sorry, if you want power, you’re going to need to buy a power meter. Plain and simple.

I started using Strava when I still had a wired SRM. So I had real power data to compare with the Strava guestimates. I found that for climbing that the averages that Strava gave were 5-12% lower than what my SRM recorded. I did this comparison using a three or four ~1 hour climbs that I climbed at the tempo/sweet spot to threshold range. For anything else it is all over the map. The guy who won the 40-44 district TT in Sattley this year (fastest on the day) had a strava estimated power of 474W average. He weighs something like 135-140 pounds. I'm pretty sure he wasn't doing 7.7 W/kg!

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Kevin

http://kevinmetcalfe.dreamhosters.com
My Strava

Without meaning to hijack the thread...

Does anyone know of a similar comparison of TrainingPeaks estimated power data vs. measured power?
My understanding is that TrainingPeaks uses the rate of vertical ascent, combined with rider weight data and a boatload of assumptions (about rolling resistance, etc.)
Presumably, like the Strava estimates, these could be quite wildly off on a lot of terrain but should be relatively good (giving a lower bound for the power output) on a steeper grade of hill. (Or am I deluding myself thinking that it's even semi-useful there?)

Any thoughts/opinions/comments?

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http://ironvision.blogspot.com ; @drSteve1663

yes, Johan Bruyneel just called and says he wants your phone number. They're looking to fill out the start list for the Vuelta.

My thought was that it's a flat out lie.
Let's see a link to the Strava account

Strava power numbers are complete BS. They report mine far too high, in general. Occasionally far too low. Sometimes they get it right. Even a blind squirrel sometimes finds a nut.

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Michael

really? That's not really fast enough I thought? Maybe my cyclocomputer needs calibratin'
anyway, I'll save up for a power meter...

It's probably calculating your power assuming your cda is that of a standard road bike with standard rider. Since you are on a TT bike, that is going to make it wildly inaccurate.

This. Strava numbers are close for me on my road bike, normal position, no wind. On the TT bike they are way high.

Would be nice if they let you define your CdA and Crr... maybe even wind for sections.

My thoughts, *cough BULLSHIT cough*

MAYBE if you're sitting in on a paceline and not doing any work, but solo? Me thinks not.