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-   -   Power estimate from Strava (https://www.bikeforums.net/showthread.php?t=1199771)

venturi95 04-29-20 06:59 PM

Power estimate from Strava
 
I am wonder those of you - bigger riders - who use power meters and Strava if you find a large discrepancy between Strava and what your power meter says. Iím about 190 pounds, 195 kitted up. 39.1 mile ride at 14.9 mph, 2,223 feet of climbing. Average power 135 watts, seems kind of low but I have never trained with a power meter. Iím not complaining, I am a barnacle along for a free ride and have only used Strava for free.

sdmc530 04-29-20 08:59 PM

I find that power on Strava is sometimes close but usually not. I am not sure how the numbers are guessed on Strava.

If you want power data you have to have it on the bike, the rest of the programs is just SWAG. Even Zwift PM numbers are elevated. Shocking right!

Power numbers are awesome data.....

topflightpro 04-30-20 07:40 AM

OP, honestly 135 AP doesn't sound too far off for that ride.

caloso 04-30-20 07:53 AM

Strava doesn’t know which way the wind is blowing, whether you’re drafting someone, or whether you’re in the drops or sitting up. So it could be way off or not.

That said, I agree with TFP: that number doesn’t seem wildly off.

rm -rf 04-30-20 08:10 AM

"real life" power numbers are pretty low for many riders. A lot less than the 200+ watts that often are mentioned in online posts.

My usual riding partner usually shows a little higher estimated watts on strava. I have a power meter, so my numbers are more accurate. Even so, there's different methods of smoothing the raw data, so I might be off by 10% or so. I'm around 170 pounds, he's 175 or so. We are both retired, and ride 4000 to 6000 miles a year.

Recently, on the same ride:
Me: 33.1 miles, 2103 feet, 14.1 mph. "avg power: 119w" "weighted avg power: 138w". (I started the recording a couple tenths of a mile into the ride. My Garmin should be fairly accurate on elevation gain.)
His estimates: 33.4 miles, 1920 feet, 13.6 mph. "average watts: 121w"

"Weighted average power" is comparable to "normalized power" It does require a power meter to include the short, hard efforts into the calculation, instead of just estimating based on speed and slope.

Strava could be fairly accurate on a long, steady climb, where most of the effort is against gravity instead of wind resistance. On the flats, it won't know about wind direction, or drafting, or even rough or smooth road surfaces. And I see my watts drop significantly when I get in the drops.

sdmc530 04-30-20 08:51 AM

So here was my last longer ride. You can see the difference between Strava and Garmin. Same ride, but different recording methods. The Garmin connect numbers are off the power meter. the Strava uses my uploaded data but get different numbers. Very interesting. They are close actually. I will see what todays ride shows.

https://i.imgur.com/azlUQQrl.png
https://i.imgur.com/KkAKXUEl.png

procrit 04-30-20 09:28 AM

Strava's estimated numbers are always lower than my power meter, sometimes by a lot. At lower speed they seem to be pretty close, but when you start averaging 20+ mph solo, they really start to diverge.

LAJ 04-30-20 09:45 AM

Estimated power from Strava is just that. If you're basing any type of training off of it, just stop.

Hermes 04-30-20 09:47 AM

Since I train to race, most of my training is structured and I choose a route or the trainer such that I can execute the workout. I upload to Strava to get segment times on the chosen route and I always have power measurement on my bike and upload data to Garmin Connect and Cycling Analytics as well. I do not get Strava measured power and my Strava feed is private.

Sometimes a Strava segment will match where I do a structured element for that days program. That segment becomes an interesting data point for comparison purposes over time.

IMO, most posters on this forum that race, use Strava to hunt KOMís and that is all about time over distance and not power. Power is ones currency to buy speed. And for racing, speed is what matters coupled with the ability to generate the required speed when it counts.

On highly structured workout days where I do hill climb repeats over / under with rest intervals, my average power and speed will be low especially if I am rolling around during the rest time. Hence, I will log time above 200 watts but not enough to up my average power for the session.

I ride a lot of 4 mile loops around Fiesta Island that is reasonably flat with a good road surface. Stava has no idea whether I am riding on the tops, hoods, drops or riding my time trial bike with race wheels, skin suit and time trial helmet.

With respect to weight, tires make a big difference and the heavier the rider the more important rubber becomes. Stava has no idea what type of tires one is riding or wheels for that matter.

I imagine that under certain wind and bike and rider setup conditions on Fiesta Island, the Strava calculated power number could be way off in either direction. However, lap times in Stava on Fiesta Island are highly accurate and based on GPS. So I find these lap times meaningful as well as lap time average speed. In racing, speed matters.

As a final note on the inaccuracy of Strava on Fiesta Island, I can improve my lap time with the same average power, road and wind conditions by execution riding the shortest distance around the island or riding on the right side of the road for the entire loop (longer distance. Traffic is one way on the island. Also, I can apply more power on the harder sections of the loop (into the wind) which will lower lap times but hold the average power constant. Strava has no way of knowing when I vary power intentionally to maintain speed due to wind.

I think Stava is a great social media platform and KOM hunting is fantastic way to compare oneself to others. Their power measurement algorithm is indicative at best and not very useful for racers doing structured training to see improvement.

venturi95 04-30-20 05:37 PM

Thanks to all the responders. I know Stravaís average power is a rough guess but Iím coming off lazy couple of years and going faster each week, the wattage doesnít seem be creeping up for the way I feel. Embarrassed to say it but that was my fastest average speed in a very long time.

Doge 04-30-20 09:35 PM

If the climb is constant 4%-8%, 15 min + and the masses are reported correctly, I think it is quite close.

On the flats - far off. I'd expect, descents are worse.

The set distance and the clock (time) is the best measure. Power is just a component.

aaronmcd 05-02-20 01:49 AM


Originally Posted by Doge (Post 21448361)
If the climb is constant 4%-8%, 15 min + and the masses are reported correctly, I think it is quite close.

On the flats - far off. I'd expect, descents are worse.

The set distance and the clock (time) is the best measure. Power is just a component.

I've noticed climbs are somewhat close with Strava estimating low, and descents Strava estimates 500 watts when I'm doing zero. Yet somehow over a whole loop Strava calories burned/average watts are pretty close if I'm solo.

OBoile 05-06-20 09:24 AM


Originally Posted by Doge (Post 21448361)
If the climb is constant 4%-8%, 15 min + and the masses are reported correctly, I think it is quite close.

On the flats - far off. I'd expect, descents are worse.

The set distance and the clock (time) is the best measure. Power is just a component.

Doge needs to step into the 21st century.

Doge 05-06-20 09:45 AM


Originally Posted by OBoile (Post 21458811)
Doge needs to step into the 21st century.

Maybe with Swift and lockdowns power is a more significant number than speed. I'll consider that.

When USACycling used to have races it was the best clock time, or first across the line that was the winner, and often not the most power.

burnthesheep 05-06-20 10:05 AM


Originally Posted by sdmc530 (Post 21447134)
So here was my last longer ride. You can see the difference between Strava and Garmin. Same ride, but different recording methods. The Garmin connect numbers are off the power meter. the Strava uses my uploaded data but get different numbers. Very interesting. They are close actually. I will see what todays ride shows.

https://i.imgur.com/azlUQQrl.png
https://i.imgur.com/KkAKXUEl.png


1. That ridden on gravel or on knobbies? If on the road, the avg power seems high given the speed/elevation for the ride.

2. One thing sticking out to me like a sore thumb here is that your TSS was 250 for about 2.5 hours. The definition of threshold and TSS calculation dictates that one hour of threshold (ftp, one hour max) is 100 TSS per hour. So, this says your ftp is set way way way too low. Test, reset, take a look at the new numbers.

topflightpro 05-06-20 12:07 PM


Originally Posted by burnthesheep (Post 21458889)
2. One thing sticking out to me like a sore thumb here is that your TSS was 250 for about 2.5 hours. The definition of threshold and TSS calculation dictates that one hour of threshold (ftp, one hour max) is 100 TSS per hour. So, this says your ftp is set way way way too low. Test, reset, take a look at the new numbers.

TSS is calculated off NP. Which in this case is just 7 watts below his FTP. He also posted a max power of 1099, which greatly distorts NP. So, FTP may be fine.

burnthesheep 05-06-20 12:45 PM


Originally Posted by topflightpro (Post 21459115)
TSS is calculated off NP. Which in this case is just 7 watts below his FTP. He also posted a max power of 1099, which greatly distorts NP. So, FTP may be fine.

Perhaps, just fishing.

It wouldn't have caught my eye at all if the ride was shorter. Like, under an hour. The longer a ride is, the more difficult it will be to maintain a high enough variability in high power to drive that kind of TSS accumulation through NP.

Do some sprints every 10min, do some 30:30's, do some 1:1......ok. That'll drive some solid NP and high TSS accumulation during that time. Do those efforts for nearly 3 hours though and often enough to drive 100TSS/hr?

It may be fine, it just caught my eye.

This is exactly why I experimented with my Excel sheet doing a "TSS/TSB/CTL" by zone. It worked OK as I'm no genius. The idea being that I accumulated 250 TSS of what exactly? Donkeys, fish, sprints, threshold, tempo? I could not get it to work yet well enough to demonstrate to me an accurate enough TSB by zone for nailing workouts (time off, frequency of intense stuff, adapt, etc....).

Idea being also that your overall TSB might go positive during intensity weeks, and without really good composure, you may be led to believe you can chew off some more work in a zone in a week than you really can. I'm horrible at that. Watching the overall CTL tank in an intensity week and get greedy and still do some long Z2/tempo ride or something to bump it up. I also feel I ramp the intensity in too quick. Like, running the TSB for a certain zone (by my idea) really negative the first day or two. Instead of "inching in".

sdmc530 05-06-20 02:01 PM


Originally Posted by burnthesheep (Post 21458889)
1. That ridden on gravel or on knobbies? If on the road, the avg power seems high given the speed/elevation for the ride.

2. One thing sticking out to me like a sore thumb here is that your TSS was 250 for about 2.5 hours. The definition of threshold and TSS calculation dictates that one hour of threshold (ftp, one hour max) is 100 TSS per hour. So, this says your ftp is set way way way too low. Test, reset, take a look at the new numbers.


So I went back and checked and my Garmin was supposed to auto adjust FTP as you ride and get fitter. When I looked this was disabled. It was stuck at 234. I was using a 520, but not to long ago updated to a 1030 and must have missed this.

So today I did a really good ride, like all out for an hour. Guess what, it gave a new FTP of 298 lol. I guess I was way to low. I know its one ride but I was apparently way off. Tomorrow I am going to do an actual FTP test and see where I am landing. I didn't do it today because I wanted to see if the auto calculations would be effected. It worked.....

who knew...thanks for noticing that.

sdmc530 05-06-20 02:03 PM


Originally Posted by topflightpro (Post 21459115)
TSS is calculated off NP. Which in this case is just 7 watts below his FTP. He also posted a max power of 1099, which greatly distorts NP. So, FTP may be fine.


Yeah, the 1099 is a very short lived reading. I am not a powerhouse by any means. There is one short steepish climb that I have to do to get back to my house and I always try to max power up it to hit a crazy power number. My record is 1124. I am trying to hit 1200 just once and I would be happy.

burnthesheep 05-06-20 03:48 PM


Originally Posted by sdmc530 (Post 21459342)
So I went back and checked and my Garmin was supposed to auto adjust FTP as you ride and get fitter. When I looked this was disabled. It was stuck at 234. I was using a 520, but not to long ago updated to a 1030 and must have missed this.

So today I did a really good ride, like all out for an hour. Guess what, it gave a new FTP of 298 lol. I guess I was way to low. I know its one ride but I was apparently way off. Tomorrow I am going to do an actual FTP test and see where I am landing. I didn't do it today because I wanted to see if the auto calculations would be effected. It worked.....

who knew...thanks for noticing that.

Great news!!

Ross520 05-06-20 05:15 PM


Originally Posted by venturi95 (Post 21446292)
I am wonder those of you - bigger riders - who use power meters and Strava if you find a large discrepancy between Strava and what your power meter says. Iím about 190 pounds, 195 kitted up. 39.1 mile ride at 14.9 mph, 2,223 feet of climbing. Average power 135 watts, seems kind of low but I have never trained with a power meter. Iím not complaining, I am a barnacle along for a free ride and have only used Strava for free.

I'm around the same weight. Here's my power from an actual meter today. I don't know what to think, just installed it a few days ago. Seems low...

https://cimg6.ibsrv.net/gimg/bikefor...4a9fe88453.png

sdmc530 05-06-20 05:40 PM

Ross520 that does seem like a lowish average, what was the normalized? How about what was the max 20 min? just curious. I seen you had a fair whack of climbing too. Did you just roll down hill quite a bit too? That will lower the average a lot as well.

Nice ride though I bet.....

burnthesheep 05-06-20 07:21 PM

Fwiw, with roller hills at 60 feet per mile I average right at 20mph solo on 190 to 205 watts. 157 pounds. Pretty aero roadie setup on good tires.

175w AP is usually around 19mph on that kind of route.

sean.hwy 06-17-20 05:27 PM


rough cliff note:
strava close when using steady power
strava shows way too much power when you sprint

Doge 06-18-20 11:36 AM

Kinda on topic/off topic. You can't always trust the grade either.
https://cimg5.ibsrv.net/gimg/bikefor...86043be2ab.png


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