High Watts Uphill With a Tailwind?

[pb21]

Would the Powerpod overestimate watts when riding uphill with a tailwind?

I’m pretty sure my Powerpod is correctly calibrated, at least more or less, but I do notice that when riding uphill with a tailwind watts shown are higher than if there was no wind or a headwind and also higher than I would expect I can achieve.

I have attached a file containing an effort I did last week (8.5 km to 9.75 km). On this stretch my average watts were 440 W, I think this is at least 50 W too high based on previous similar efforts, I don’t think I am able to sustain 440 W for 5-minutes.

On this stretch there was a tailwind, which according to mywindsock was around 15 mph, I guess at ground level this would be lower (https://mywindsock.com/activity/1097383704/).

Do you see any reason why this would be wrong?

I am probably being stupid but does the wind ‘pushing’ you make any difference, or is this all taken into account by your relative wind speed?

Hills certainly feel easier with a tailwind because of being pushed on?

[Velocomp]

You are a better cyclist than you think...

I don't see any problems in your climbs. The "tail wind" actually reduces the watts, relative to a no-wind or headwind alternative.

The reason you see tail winds on your climbs is that, because they are steep, you are moving up the mountain slowly. It is difficult to measure wind speed accurately at really low speeds. Fortunately, low wind speeds don't contribute any substantial opposing force (12W out of 518 on your steepest climb around KM 9), so it does not make any difference.

You climb the KM 9 area at 16.2 km/hr; the next climb is lower watts, but you ascend it at a lower speed of 15.3 km/h.

I think your PP is working just fine.

[pb21]

Thanks for your reply, maybe I am better than I think!

So does riding at 15 mph with a 15 mph tailwind mean that as my relative wind speed is 0 mph the only opposing forces are gravity and friction? Would there not be a supporting force too, or if there is would that be negligible?

[Velocomp]

If you're riding 15 mph with a 15 mph tail wind, then the wind speed measured by PP would be zero.

If the tail wind speed is GREATER than bike speed, then there would be a "supportive" force from the wind. PP would not measure that supportive force accurately. But if you have a tail wind greater than bike speed, you're probably riding too slow...

This would mean that the only opposing forces would be hill slope, acceleration, and friction.

[pb21]

Excellent!

I rode a similar hill yesterday and got similar numbers, albeit with no particular wind of note, which gives me confidence!

Thanks for your replies.

Edit:

Actually the first 50 seconds of his effort the power reading was 0 W, which was a bit annoying, i assumed the PP was not picking up the speed sensor signal but I have just looked at the ibr file and there is speed data for that section, but not cadence. The effort in question begins at 17.25 km (40:54).

Are you able to post process the data to give power for that full period?

[pb21]

I have saved the effort only ibr file attached to this post.

It would be really useful if I could add the power to the first 50/60 s, is that possible?

Edit:

Scrap that, just found the repair for missing cadence feature, great stuff!

[Velocomp]

Great!