Why is my Flux power so low?

Anything about Power (watts)

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Why is my Flux power so low?

Post by hanskohls » Tue Feb 28, 2017 2:49 pm

To put it straight I am unfit, but I am very surprised by the wattage output of my Flux after having it for a week.

I never used to have a power meter, but I've just come from my physio where I was asked to ride a stationary bike to warm up. While I doubt the wattage to be precise, I spent 10 minutes putting in 200w and reaching 5k distance 30kph, a speed I tend to aim for during 15-20 minutes segments on flat roads with no headwind. This was a fast (cadence 95) but low resistance warmup. I was literally just on the verge of breaking a sweat, fully able to talk to the therapist without shortness of breath.

Now I have not been cycling much in 2016 and my fitness is not what it was at the end of 2015, when I was out on the road almost every weekend and commuted 36k two or three times some weeks. So I went to Strava to compare some key runs:

The first run I looked at was my very first test commuting to work in 2015. I had barely done 5km on a pretty new bike before starting this ride and I did not cycle or otherwise exercise much for 7 years leading to this ride. I still averaged according to Starva's estimate 147 watts and cycled a total of 18.8 km in 50 minutes (including regular slowing down and accelerating for traffic etc).

Another run last autum was a 2 hour run around Loch Leven in Scotland, where I did a round trip of 37.5km in 1:51 with a total elevation of 405m in 1h52. Strava recons my average power was 166.

On my Flux with TrainerRoad I feel the power estimate is far lower than Strava or the stat bike at the physio:

About 10 days ago I did an FPT test (20 minute test on TR) and reached an average power of 113w and an FTP of 131w. I really worked full-on during this test, reaching a total distance of 17.6km over the hour. Strava reckons my speed during the actual test interval was no more than 25kph, I know on the road at that power I'd be well above that.

Yesterday I did the 90 minute Antelope+1 workout (My 6th TR workout at a duration of 1-2hours) and my weighted avg Power was 108, with several intervals at 122. This was really hard for me to keep the cadence up and I really suffered through each of the intervals. Yet the power according to the Flux was barely 60% of the power I did on the physio's bike where I was happily chatting away. The total distance ridden was 23.7k in 90 minutes.

Going back to my real life ride last year vs. my TR ride yesterday. If the Flux watts are right, then:
  • My fitness would have decreased so much that in 90 minutes TR I would have ridden 14k less than in a 20 minute longer ride with 400m elevation last spring.
  • My current FTP would be 35w less than what Strava estimated based on a ride last year as the 1:50 average watts.

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Joined: Sat Nov 04, 2017 7:30 pm

Re: Why is my Flux power so low?

Post by dogzilla » Sat Nov 04, 2017 7:35 pm

Strava estimated power is a load of rubbish, it's completely inaccurate 9/10 by a WIDE margin. Only very occasionally it will come up with an average power level that is within 10% of actual power.

Speed and distance on a stationary wattbike are completely irrelevant too because it has to estimate the effect of weight + air resistance.

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