bonsai171

Has anybody compared Strava's average power numbers to an actual power meter? I dont really expect Strava's numbers to be accurate, but am curious if they are high or low compared to a power meter.

Dave

WhyFi

I think that it really depends on your riding style. In general, I think their estimates are in the ballpark over the entirety of a ride (shorter durations are a joke, except for maybe a very steady climb), if you've got your weight and bike info entered correctly/honestly, but it still can vary based on other factors. For me, it tended to be a little low, but not absurdly so.

bonsai171

I have my bike info dialed in. Maybe just need to train more to get the power up. Sometimes it says 600 or 700 watts on a climb though. Was in decent shape a few months ago but stopped riding after a surgery. Think the power meter is worth having?

Dave

mr_pedro

If weight is set up correctly, the biggest factor that makes strava power inaccurate is wind. On climbs it can be better provided it has accurate data for the incline. The power peaks are not accurate at all, which is what you refer to when you say 600W or 700W., I assume?

If you should get one? What are your goals, what do you intend to do with it?
The data it provides is fun in itself. But the way a power meter makes you faster is by allowing you to follow a structured training program, measuring your fitness level and then ride hard on hard days and ride slow on slow days. You can use heart rate for that, but that does not work for measuring intensity of short intervals.

bonsai171

I'm assuming the 600 and 700 watt numbers are peaks. Some of those numbers showed up as my power numbers for segments.

I would like to get faster next year than this year. Did a heartrate threshold test (I think that's what it's called) and went up a little from the prior year. Know of any good training programs?

Dave

mr_pedro

The segment power numbers in Strava are average power figures over the entire segment. Pro level cyclists can do 600-700 W for about 4 minutes. For many people that is their 3s sprint power.

The links below give you an idea of how a plan looks like and provide examples of plans you can follow.
https://www.cyclist.co.uk/tutorials/...-training-plan
https://www.cyclingweekly.com/fitnes...g-plans-153049

Seattle Forrest

Power meters are great for lots of reasons, but they're expensive and most add weight to the bike. So it's only worth having if you use / benefit from the data. You can call me captain obvious.

They can be useful for training of you're willing to put the work in, and also some computer time. Not much. The numbers the thing spits out need context. That context is how much power you can do over different time frames.

canklecat

Strava's power guesstimate works like other online power calculators, minus any way to factor in headwind resistance or tailwind assist, or drafting effect in a group. There are two or three online calculators that all use the same basic formulas, and you can enter wind factors to get a closer power guesstimate.

rubiksoval

Totally useless.

Consider this: Strava has no idea if you're riding with a 10 mph headwind or a 10 mph tailwind. Strava doesn't know if you're riding 28cm gatorskins with butyl, or 25mm corsa speed tubeless. Strava doesn't know if you're solo or in a 100 person peloton. Doesn't know if the road is horrific chip and seal or new pristine asphalt. Doesn't know if you're sitting bolt upright riding with no hands or are in the supertuck position, if you're wearing a puffy jacket or a skinsuit.

All of those things matter significantly in power output needed for a given speed.

To show an extreme example: I've done the same power going 20 miles in an hour as I have going 31.5 miles in an hour. Strava's estimate differs by about 200 watts...

rubiksoval

Those numbers don't mean anything.

You would definitely know if you were doing 600-700 watts. My strong suspicion is that you were not doing anywhere close to those numbers, and 100% without a doubt you were not doing those numbers for entire segments.

spelger

i've seen this question come up from time to time and the same two answers generally are given:

• estimated power is not all that bad but...
• estimated power is crap because...

regardless of the answer my question is how do you know? i have my own doubts about their estimated power which, ironically, is mostly due to the reasons that both camps give. the only way i can see to get an honest answer is to upload a ride without power data and compare with the same ride containing power data. has anyone done that? it falls on someone with a power meter to do this. if i had one i'd give it a whirl just to see.

bonsai171

Thanks. You are in my head lol.

Dave

mr_pedro

https://www.strava.com/activities/4502120904 -> Strava Power 195W avg
https://www.strava.com/activities/4401705368 -> Power meter 236W avg

Also if you look at the power over individual segments the numbers are even more off.
If you are not used power numbers the averages might seem not too far off, but it is a huge difference.
With an FTP of 250-ish W, for me to ride 1.5 hours in traffic with an avg of 236W is right at the limit, which it was.
A ride with 40W less sits one zone below, it is like going fast but without pushing it.

spelger

Thanks, glad someone took the time to do this. as i mentioned, i don't have a PM but do have a trainer with power built in. i was thinking i would take one of my rides and strip out the power and shove it back up to see what the estimates were. thanks.

i noticed too that the speed is not exactly the same (different max speeds) and the elevation is 90 ft different but cadence and heart rate were the same. were these created from different devices?

speaking of elevation, bummer, flat land. looks like an ant hill is the biggest you encounter over there. i was stationed across the water in england years ago and it was flat like a pan too. now i am surrounded by mountains everywhere i look.

-scott

ericcox

While I haven't done exactly this, I did use Strava prior to getting a power meter in October. While I have gotten stronger over the past few months, I saw an immediate difference in my actual vs. estimated power on the same routes. My estimated was 30-50 lower than measured in the weeks after I got the pm. Not scientific by any means, it makes sense given how much wind I ride in and the relatively short hills in my area. I can't give an exact number or percentage, but estimated for me is lower.

mr_pedro

Strava uses gps position over time to calculate power, data from trainer won’t work.
Same device was used, I used https://gotoes.org/strava/index.php to process the file. I took the original file from Garmin and stripped out power and randomized date tags so Strava does not reject as duplicate ride.
Speed and time, also for the segments look similar. Strava does a lot of processing to the files to show all the stats, maybe the randomization had an impact.

Yes, it is flat over here. People sometimes use bridges and overpasses to train climbing.

rubiksoval

We know because we have actual power meters.

Yes, many times.

Can also get an idea from comparing group rides from similar riders with and without power meters, or even comparing strava segments.

Suffice to say, it isn't an argument. Estimated power is absolutely nothing to pay attention, to. Anyone claiming it's "not that bad" simply doesn't understand what affects power, and why even small deviations can impact training and performance if power is being used for that.

WhyFi

It's a matter of perspective and expectations, I think.

You're right that it doesn't have any value when it comes to actively training. But when it comes to tracking progress of someone new or newly-invested in cycling? I think that the window of error is too wide to put any stock in "analysis" of shorter efforts or even single rides, but, in aggregate and paired with RPE, it may be all that they want or need - some kind of affirmation that they're trending in the right direction.

Should someone strut around at the café stop because Strava estimated that their last ride averaged ### watts? God, no. Would I recommend a power meter to anyone more with than idle curiosity and the means to scrape together a few hundred bucks? Yeah, for sure.

Sy Reene

How much closer to accurate would Strava be if riding in Watopia?

WhyFi

Wut.

Sy Reene

A place with no wind, no chipseal, etc. ie. a number of the factors supposedly that make Strava estimates inaccurate.

WhyFi

To move along in Watopia, you first need power or an estimation thereof (zPower).

Sy Reene

I know. It was a just a theoretical question. You could have a power meter (eg. in the trainer) but still have Strava do an estimate if you don't upload the ride from Zwift.

EDIT: Actually I take that back. I'm not sure if there's a way to take a Zwift environment ride and send it to Strava without power numbers attached?

mr_pedro

It is possible, you can just download the zwift ride from Strava, strip the power out, e.g. using the online tool I linked above, and reupload to strava.

Accuracy will totally depend on Zwift and Strava using the same power calculation engine and better not draft in Zwift.

WhyFi

Ah. So a question with no practical application and little academic value ("does math work/how much is lost in translation?").

Got it. Carry on.