Unusual technical questions

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Unusual technical questions

Postby ldrcycles » Mon Aug 08, 2011 1:46 pm

Such as: if i'm riding into a 10kmh headwind and doing 27kmh, is that the same as doing 37 in still air? I am cursed when it comes to headwinds so that's how i deal with it mentally lol.
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by BNA » Mon Aug 08, 2011 2:05 pm

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Re: Unusual technical questions

Postby Chef » Mon Aug 08, 2011 2:05 pm

Fair enough - but make sure you deduct from your speed when you have a tail wind :D
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Re: Unusual technical questions

Postby goneriding » Mon Aug 08, 2011 2:35 pm

Chef wrote:... tail wind :D


There's no such thing!
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Re: Unusual technical questions

Postby BarryTas » Mon Aug 08, 2011 2:39 pm

my bike computer "random" stops working. It's not going up or down hill just in some "random" spots or zones. I "random" as it always happens at the same seemingly unrelated spots. I blames the magic, ninja, alien fairies
when do we stop for coffee???

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Re: Unusual technical questions

Postby you cannot be sirrus » Mon Aug 08, 2011 3:42 pm

If my average speed is 30km/h and I cycle with a tailwind at 35km/h, why can't I ride into the wind at 25km/h?
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Re: Unusual technical questions

Postby Alex Simmons/RST » Mon Aug 08, 2011 3:53 pm

ldrcycles wrote:Such as: if i'm riding into a 10kmh headwind and doing 27kmh, is that the same as doing 37 in still air? I am cursed when it comes to headwinds so that's how i deal with it mentally lol.

Head and tailwinds are not linear scenarios.

i. power required to over come air resistance is proportional to the (square of relative air speed) x (ground speed)
ii. power required to overcome rolling resistance is proportional to ground speed

so
in case of i, while the relative air speed is same in each scenario, the ground speed is not, and
in case if ii. the rolling resistance is lower at slower speeds.
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Re: Unusual technical questions

Postby BarryTas » Mon Aug 08, 2011 4:03 pm

Alex Simmons/RST wrote:
ldrcycles wrote:Such as: if i'm riding into a 10kmh headwind and doing 27kmh, is that the same as doing 37 in still air? I am cursed when it comes to headwinds so that's how i deal with it mentally lol.

Head and tailwinds are not linear scenarios.

i. power required to over come air resistance is proportional to the (square of relative air speed) x (ground speed)
ii. power required to overcome rolling resistance is proportional to ground speed

so
in case of i, while the relative air speed is same in each scenario, the ground speed is not, and
in case if ii. the rolling resistance is lower at slower speeds.



science!!!
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Re: Unusual technical questions

Postby snark » Mon Aug 08, 2011 11:23 pm

you cannot be sirrus wrote:If my average speed is 30km/h and I cycle with a tailwind at 35km/h, why can't I ride into the wind at 25km/h?


No idea about the "why", but here's a recent example curtesy of the weather bureau and a Garmin Edge 500: With a 20km/h north wind, I was sitting between 35-38km/h heading south over a reasonably long section of road and 23-36km/h heading back on the same section of road (on a road bike with 23mm tyres). If someone does the math, let me know if that's expected :).

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