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Calculating side winds

Old 10-19-10, 04:25 PM
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TomD77
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Calculating side winds

I don't carry an MP3 player or anything else with me on rides so I have thinking time. You would think that a wind coming from your 9:00 or 3:00 position would have no effect on your speed or effort but it sure doesn't feel that way when you get hit by a gust from the side.

Just playing with even numbers, say you're riding at 20 mph and there is a 10 mph wind at your 3:00. The felt wind will be 22.3 mph coming from your 1:00. Keeping numbers round, instead of having to bore a hole in the air at 30 feet per second, the hole is bored at 33.5 feet per second. Considering that the energy cost of moving air out of the way increases as to the square of your velocity, the side wind cost you 25% more effort to maintain speed. Things get worse rapidly as the wind shifts to your front but the wind probably has to be from 4:00 or further back before it doesn't cost you.

If there are any errors in my reasoning, I'd like to know it.

I live in northern Florida where there are relatively few days through the winter where it is too nasty to ride but there sure is a lot of air in a real hurry to be somewhere else.
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Old 10-19-10, 05:34 PM
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That pretty much sums up 'standard wisdom.' Which is why a wind always hurts you on a loop-type or out-and-back ride where you end up at the same place you started: The wind really is against you more than it's with you.
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Old 10-19-10, 05:46 PM
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In your scenario I make the apparent wind 22.4mph from 26.6 degrees off your heading (just shy of your 1:00) so your numbers are good.

I understand how much the wind sucks, especially now that I mostly commute on my lowracer recumbent. We get the afternoon nor-easter here in summer which blows consistently most days and peaks in strength right at my home commute time which happens to be directly into it along a long, exposed stretch of freeway. I often cruise by groups of hardcore roadies pacelining into that headwind and recall how frustrating some of my commutes used to be. These days I save the fully fendered Surly for the rainy days.

Edit: I'd kill for a NoComm along that commute... one day maybe
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Old 10-20-10, 10:39 AM
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Stop thinking- I now have a headache wondering what else you get up to on rides.
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Old 10-20-10, 01:07 PM
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Learned about the apparent wind early as a kid while racing small sailboats. Seems unfair that the faster you go, it just rotates closer and closer to your nose!
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Old 10-20-10, 01:26 PM
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Click on "Apparent Wind Calculator": http://www.hedcycling.com/aerodynami...calculator.asp
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Old 10-20-10, 02:48 PM
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Originally Posted by Shimagnolo View Post
Click on "Apparent Wind Calculator": http://www.hedcycling.com/aerodynami...calculator.asp
Hey thanks! That's handy. Why worry about vectors and trig when a java app can do it as fast as you can frame the question?

Playing around with it just confirms my intuition, wind isn't your friend. Other than biking, I have two other main hobbies: long distance target shooting and offshore fishing and a good wind will wreck a day of either.
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