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Comment by malfist | Hacker News Reader

100W is pretty high for an untrained person. Back when I was cycling regularly I could hit those numbers but not every time. I took my first ride of the season and averaged a whooping 63 watts. Stealing 5 watts from that it taking away 8% of my energy. If you account for efficiency loss in the dynamic it's probably closer to 16% of my output. That's a huge chunk

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You need to take you into account that the required power output scales quadratic with the speed. Power in itself means nothing, speed is what matters in the end. If you run the math (and various cycling blogs and magazines have done so), you end up with speed reductions in the order of less than 1% or fractions of a minute per hour cycled. You’d likely gain more by wearing clothing that has less drag.

8% less power would imply between 0.92 and towards 0.92^0.5 times lower speed depending on if you are in the mainly linear or mainly quadratic region of resistance.

Older dynamos with a bulb connected were quite tiresome to propell.

The 8% are at the top of the power output - at the bottom end, the fraction doesn't matter. You'll be able to provide 5W more if you're only pedaling at 50W.

The old dynamos were a chore. But their efficiency pales in comparison to a solid hub dynamo :)

A 63 watt average must have been taking into account all the time you weren't pedalling, that's extremely low - you would struggle to ride into a slight breeze.

It's certainly possible for a leisure ride - 100W give you ballpark 20-25km/hour. The drag scales quadratic, so if you go below 20km/h, you'll end up somewhere in the region of 63W average. Peak output would still exceed 100W.

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