chaadster

I'm curious why Strava underestimates my power so much? I've been training on a Cycleops 300PT Pro for a couple of years now, and I have a PowerTap wheel on my spring/trainer bike, so I know my power numbers pretty well, and am sure Strava is way low when I ride my meter-less bike.

It's not a big deal or anything, but I do wonder if there's a setting somewhere in Strava that I can adjust to bring the numbers closer to reality? I mean, I'm looking at Strava anyway, so why not if it's possible?

Obviously a power meter for the bike in question would straighten things out, but other than that, anything I can do? My weight is correct in Strava (ok, maybe 5lbs light right now!).

Zuzus pedals

Provide Strava with a different value for your weight. Even then, things won't always be accurate. Strava can't tell when you rode with or against the wind and doesn't know the weight of your bike (at least I don't have those features as a non-premium member). And it's a problem with GPS, not Strava, when a climb's elevation is measured from the water level under a bridge you've started on. That'll throw off the VAM and the power numbers. There are plenty of factors that can create false readings if a restrictive formula is used to estimate power, so an actual power meter is the best way to go.

cydewaze

I think Strava is best used when used to measure improvement over previous efforts rather than to calculate actual measurements. For me, it's constantly arguing with my Garmin over things like calories and feet climbed, even though the Garmin should be more accurate on those since it knows my bike weight and heart rate.

bt

why does it matter to you?

jmX

So for every ride you want to tell strava how many minutes you spent on the hoods, in the drops, and on the tops? How much did you draft? What about how loose your jacket was, how inflated your tires were, what the roughness of the road was, and what your weight was of both you and the bike that day? Maybe you need to measure your hip girth too to figure out how much frontal area they take, as well as what kind of road bike you have and how deep your wheels are. Would you really do this? Probably not.

The only time strava's numbers will be anywhere near consistently accurate are on a steep climb at least a minute or two long where aerodynamics are almost unimportant, and even then you need to make absolutely sure you've got your weight and your bikes weight entered properly.

Elvo

Get an anometer, thermometer, and barometer and subtract/add watts as needed to account for wind resistance.

chaadster

I guess what I was getting at was more a question of how Strava estimates moreso than why estimates are problematic, and specifically whether Strava plugs heartrate info into the power estimation algorithm, and if so, if that can be calibrated differently. My thought here being that, if as Cycleops contends and DCRainmaker confirms, using HR to calculate power produces a more workable number, then why not try to dial that in to get a more accurate picture of what the rides are like one to another since I'm looking at Strava regardless?

I suppose this is one for Strava's help desk. They probably don't use HR, and if they do, probably don't have a calibration protocol like Cycleops does for Powercal; probably would have heard about it. Oh well, can't hurt to ask.

Thanks for the replies, folks.

chaadster

Right, exactly my interest. However, it seems like my power numbers never fluctuate meaningfully based on effort, or at least the 10-15 watt variance is below my sensibility threshold! Part of the issue is certainly that I don't look at Strava power estimates closely enough to use as a metric because they seem so far off. If it's there to be a tool, it doesn't work for me now and I'd like it to. If it's just window dressing, that's fine too, but I just want to make sure one way or the other.

dave1442397

Try this Chrome plug-in and see if it gives you more useful data (text below copied from developer's post) -

Here is a chrome extension you should try => https://bitly.com/stravaplus

As a rider and computer science engineer, i developed the "StravaPlus chrome extension" to improve my strava web experience. Decided to share this with you and not keep that only for me !

# The features in version 0.1.13 are:

- Standard deviation speed data
- Lower quartile, Median, Upper quartile speed
-Pedaling data (pedaling %, pedaling Time and crank revolutions)
- Motivation Score
- Stress Score
- Activity Ratio
- Estimated Normalized Power
- Estimated Variability Index
- Estimated Intensity Factor
- Normalized Watts / Kg
- Display Bike odo in activities
- Default Google Map type in activity page
- Segment Rank %
- Default Leaderboard Filter in segments
- Hide challenges in Dashboard
- Hide created routes in Dashboard
- Kom Map integration
- VeloViewer Trophy case link integration
- Integration of RaceShape / VeloViewer / FlyBy
- Hide premium if your are free account
- Ergonomics and infos improved

cydewaze

Wow, that's a really awesome extension. Lots of additional info! Thanks for the link.

rangerdavid

get a power meter

Caliper

In your profile, under gear, you can add your bike(s) and their weight even as a free member (as I am). It's not the most intuitive thing to get into, but it also lets you track mileage on a given bike and more importantly on components. You can add your tires, chain, cassette and see how many miles you have on them since putting them on.

For the OP, if you haven't set up the bike in the gear page, another thing it asks is MTB/CX/Road bike, which has got to play in to the power estimate due to tires. I've also thought that weights should probably be ready-to-ride weights, so with your helmet, shoes, spare tire/tube/pump and any food you take with you.

Zuzus pedals

Ah! Finally found that option. Missed it when first setting up a profile. Thought about entering the weight of the bike at some ridiculous number that would suggest that it had an abandoned boat anchor as the front fork, which would make my power estimate go way up ... but I still wouldn't actually have any more power and it wouldn't make me go any faster, and faster is the goal.

floridamtb

I don't think Strava takes bridge elevation into account, at least not in pan flat South Florida. I can cross the tallest drawbridge (about 65 foot climb) several times on a ride and Strava says I climbed 0 feet

wphamilton

Maybe use the android app Bicycle Power Meter and upload the .tcx file (with power) to Strava. It is more configurable than Strava, although the developers don't claim better than 85% agreement with actual power meters.

chaadster

Thanks, looks interesting, and I would like to try it, but I don't use Chrome at this time. I may install it to check it out. Thanks again.

mtalinm

look for the setting named "Do a Less Sucky Job Of Imputing Power Without a Power Meter."

seriously, if it were easy to do without a power meter, we wouldn't need power meters. the PowerCal is not bad for estimating overall ride power, but second-to-second it will be way off.

my guess is that Strava put this in to reduce support requests from n00Bs asking "can you compute power?" the CEO has a PhD in economics and is no dummy.

chaadster

Don't understand why it's hard to grasp that Strava isn't doing for me even what Powercal does, or why it's so hard to imagine Strava doing a better job. If you're pumping HR info into Strava, it has the same-- no, more!-- resources to calculate power than a Powercal does, and more computing power.

kv501

Is it an option for you to sell your existing PM, put the funds towards a PowerTap, and then have real power for both rides just by swapping wheels?

Not trying to be facetious; honest question.

RChung

It may be possible but Strava doesn't seem very interested in implementing it.

Many riders have made comparisons of power measured by a PM and Strava. Here's one that I saw relatively recently:
How accurate is calculated power / calories? ? Dave McCraw

GatsbyGlen

Wow, I was browsing for info related to Strava's Power estimations and came across this extension. Excellent! Thanks!!

Homebrew01

Buy a used Powertap for $200 or so and get real numbers.

Jeremy_S

I can't see strava ever being genuinely close with power. I guess it's a good guess but when you look at segment by segment and a 2 miles climb that had my heart exploding as I tried to beat my last time got an average of 84w and the following 4 mile flat/decent that I averaged 27 mph on although I wasn't putting in squat for effort comparatively averaged 300w....

theres only so so much you can do I would think.

Next at time I feel like blowing a chunk of cash on something bike related I'll get a stages ultegra crank arm or Garmin pedals. Probably the pedals so I can go bike to bike.

Dan333SP

He has one. Did you guys read the op?

Homebrew01

Uhhh .... ummm. hmmmm ....errrrr, wellll .....ooops