indyfabz

And ad for Cheetos would have been downright eerie.

smarkinson

Don't say I never do anything for you suckers:

Ride with power meter (4iiii):
https://www.strava.com/activities/855256396

Same ride with power meter data stripped so power is Strava calculated:
https://www.strava.com/activities/858782646

Around 15-20% down in the Strava power for most segments although the one high speed downhill segment (Bexhill Blast) it is only down 4%.

RPK79

Now ride into a headwind and with a tailwind and tell us the variances.

chaadster

I've done the same, recorded a ride with Strava on my phone app with only HR input, and simultaneously recorded the same ride on my Garmin E500 with HR, power meter, and speed/cad inputs. Strava estimates were always significantly lower than actual.

I have no idea how one could reasonably compare a Strava estimate for a real road ride to a trainer session power. Doing do makes no sense; even based on segments or intervals using RPE, there is no reason to expect the power results to be the same.

Sy Reene

So, the big question is.. if it seems true that Strava universally underestimates power outputs, how the heck doesn't Strava know this already and would have already addressed this?

On an aside.. how does everyone know that power meters aren't vanity-built to please its purchasers?

caloso

If that were the case, mine would be broken, as it usually fails to please me.

PepeM

If they all gave inflated numbers then that would render the whole thing useless, because then no one's numbers would be inflated with respect to everyone else's.

Sy Reene

So what's your point? I now fit in a size 00 miniskirt; 5 years ago I used to be size 4.. but my weight has stayed the same.

Sy Reene

So I took a look at a ride in Strava. FWIW I recommend that if you don't already have it, get the Stravistix plug-in for extended statistics for Strava. Anyway, so there are 2 separate Avg Power readings. The original one that basic Strava tells you and the Stravistix reading which is labelled as "Estimated Weighted Avg Power (a Dr Coggan formula)"

The DrCoggan version is often about 50% higher than the generic Estimated Avg Power (eg. 210 vs 140). I much prefer believing the Dr Coggan version. ymmv

gregf83 

That's also called normalized power and it gives more weight to higher power efforts. If you ride steadily the numbers will be identical. The difference is larger on Strava with power estimates as their estimates tend to be 'spiky' which raises NP.

gregf83 

Because power meters use a very simple formula to calculate power: torque x angular velocity (Cadence). You can check the torque measurement on many powermeters by carefully hanging a known weight from the pedal.

Strava can correct their measurements when everyone agrees to ride the same bike with the same tires in exactly the same position and identical clothes.

lsberrios1 

Watts could also be measured in horsepower. Most of us basically average about 0.3 hp per ride

WhyFi

Doubtful.

PepeM

Good point.

I will conclude that if Strava is estimating your power too low, you need to slam that stem.

PepeM

I wish.

EDIT: Also, you mean power can be measured in horsepower. #pedantalert

Dan333SP

Please tell me you're a lady...

Dan333SP

We saw enough ads for Cheetos during the campaign season.

redfooj

Specialized riders are strong.

hsuehhwa

The wind direction is the main factor that determines if Strava's estimate is under or over.

SpeshulEd 

As an analyst, I'd like to point out that junk data is junk.

If you care that much about your power reading, buy a power meter.

redfooj

flat road, with typical values for system weight, drive train loss, rolling resistance, and air density



and a modest 5% grade, with same values as above




on the flat, speed is all about aero drag and strava has only 3 models (based on your bike type road, cx, or mtb)... maybe it also scales your frontal area based on weight but point is, theres potential for huge error between your actual setup and strava estimated. your bike's actual condition / "efficiency" and rolling resistance means very little.

on the hill, its all about gravity. unless you ride on the moon, the strava model has got this variable pegged. so its power estimate is very good since the rest of the variable means very little.

lsberrios1 

And having a power meter does not mean that it is an accurate reading. You must have at least 3 power meters to then average the readings and come to a meaningfull conclusion.

Dan333SP

Correct.

PepeM

Don't forget to calibrate them before every ride. Also mid-ride if the temperature changes more than a few degrees while you're riding. I always bring a 20lb certified weight with me for that purpose.

Dan333SP

Are we talking about your STEELSTEED here?