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wattage output on strava

Old 08-01-18, 05:13 PM
  #1  
Baldy1953
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wattage output on strava

Not sure this is the place to ask this.
I have noticed on some segments my wattage is quite a bit less than others and yet I am doing the segment in a lesser amount of time. Today I did a segment and it is showing 61 watts less for me, yet I was 10 seconds faster than the person behind me. Perhaps, I do not understand the wattage stat in Strava. From what I have read on here, there are some that are much more in tune with the statistical info than I.

Would appreciate some clarification, but humor is always welcome.. Come on, enlighten me!
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Old 08-01-18, 05:44 PM
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SylvainG
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For the same segment, weight is probably the difference here.

https://support.strava.com/hc/en-us/...lculates-Power

"To ensure power estimates are as accurate as possible, make sure you have accurate weight data for your bike, and yourself"
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Old 08-01-18, 05:53 PM
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Baldy1953
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Thanks SylvainG. I looked at my strava account and the info is correct for my weight as well as the bikes. I am only a free strava user. would that make a difference?
I am just curious. Just wondering how conditioning plays a part in wattage, if any. Not really that important as I am still going to ride.
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Old 08-01-18, 06:00 PM
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SylvainG
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May be your data is correct but who's to say the other user's data IS correct? Conditioning will affect the power you can put out, but for the same speed, surface level, weight, wind, tire and gearing resistance, you should require the same amount of power.
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Old 08-01-18, 06:14 PM
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Baldy1953
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This could be a correct assumption. The disparity appears in several different segments. I am sure if i look hard enough for an explanation I will find one. LOL
Might take more effort than it is worth.
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Old 08-01-18, 06:37 PM
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The Strava Wattage Guesstimator 5000 cannot account for unknown variables. At it's best case, it will know your weight and height, and the weight of the bike. It doesn't (and cannot) know about rolling resistance, the prevailing wind, or whether or not you were solo, pacelining, or drafting a delivery van. So the power numbers it spits out might as well be from a random number generator.

Want to know your power output? Power meter. Everything else is guessing.
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Old 08-01-18, 09:58 PM
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Originally Posted by DrIsotope View Post
The Strava Wattage Guesstimator 5000 cannot account for unknown variables. At it's best case, it will know your weight and height, and the weight of the bike. It doesn't (and cannot) know about rolling resistance, the prevailing wind, or whether or not you were solo, pacelining, or drafting a delivery van. So the power numbers it spits out might as well be from a random number generator.

Want to know your power output? Power meter. Everything else is guessing.
Strava Watts (my term for them, they're not real Watts) DO take into account the type of bike that you put in. Swithing Road/CX/MTB will (or at least did for me at some point) change the Strava Watts reported for activities with that bike.

But... I agree, Strava does not know when I'm riding on dirt roads the day after a rain. Huge difference in watts there. I really only compare my Strava Watts to my own activities. Well, and the pros, but only when my numbers are close to theirs.
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Old 08-01-18, 11:02 PM
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Lots of variables, as other folks mentioned. I don't use a power meter but I've noticed my Strava guesstimates are awfully close to the folks I know who do use power meters and are about my size, weight, etc. The main difference is most of them are riding lighter bikes. But it's close enough within 10 watts, give or take. I'm mostly interested to see that I'm gradually holding a little more power over distance and on some difficult segments compared with last year, on the same bike and weighing about the same. Good enough for my purposes. I don't need a power meter to remind me that I'm still a slug compared with most guys my age.
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Old 08-02-18, 05:30 AM
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In addition to all the unknown variables mentioned, weight will have an impact. The lighter you and your bike are, the less power you need to ride a certain speed compared to a heavier rider and bike so unless you and the other guy weigh the same, they aren't exactly comparable. Although the difference isn't that much on flats (according to the online calculators that I've played with), but the difference gets more significant the steeper the climb.
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Old 08-02-18, 11:54 AM
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Unless the segment is pretty much windless and at least 5% grade, Strava power can prove pretty worthless. Instead, it's better to track your own personal times on segments over time. Do the segment 30x a year, click on segment, make sure the curve is going the right direction.

Otherwise, real power or HRM is where it's at.

Strava power succombs to issues of wind, wrong weight, and plethora of other variables to be reliable on anything but a serious hill. On the hill, wind isn't as much an issue and if your weight is correct.......your VAM is a good indicator of weight and power.

In other words, don't worry about it. Even with real power you run into people not counting zeros and inflating their power. Or, people setting autopause to 10mph to have stellar average speeds.
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Old 08-02-18, 12:55 PM
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What confuses me is the graphing. I'll put my cursor on a peak, and it'll read 140 watts. But halfway off the peak, it'll read 800 watts. 'Watts' with that???
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Old 08-02-18, 01:49 PM
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Originally Posted by BlazingPedals View Post
What confuses me is the graphing. I'll put my cursor on a peak, and it'll read 140 watts. But halfway off the peak, it'll read 800 watts. 'Watts' with that???
I suspect it due to a artifact (bug) of their graphing code, which is due to smoothing the calculated peaks. Each instant of time, Strava calculates an estimated "power" based on the velocity and grade at that instant, and on the velocity from the previous instant. Since they'd need to use change in velocity as well as the instantaneous velocity for the power during that time interval. As a result (and because the GPS isn't all that precise) that would be a pretty jagged graph with spurious peaks, so you "smooth" the data points - the simplest way is just an average or the last 2 or 3, but there are several smoothing algorithms. Somewhere in that process, Strava has the data shifted in the time interval, not binding it properly to the displayed data point in the graph.

It would also look like that if they showed the raw un-smoothed value but that would be more random so I don't think that's it.
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Old 08-02-18, 04:45 PM
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Originally Posted by BlazingPedals View Post
What confuses me is the graphing. I'll put my cursor on a peak, and it'll read 140 watts. But halfway off the peak, it'll read 800 watts. 'Watts' with that???
You might also try zooming in to better see the individual fluctuations in their calculation and better put the cursor on the actual peak.

The only place I see a really good looking graph is a sustained effort up a fairly steep hill. This might also be a good place to compare oneself to others since most of the wattage is involved in lugging your weight up the hill and many of the other variables are a lower percentage of the total.
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