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Old 10-30-09, 11:02 AM   #1
raybo
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How does wind affect distance?

I have another physics question (humor prompter) for the board.

How does wind affect distance? Does a 5 MPH headwind reduce daily mileage effort by 5 miles, or another one of these 1 for 1 ratios? Do tailwinds add what headwinds take away?

The reason I am asking these questions is that I am working on a bike touring specific application that involves these parameters. When I have finished the application (months from now), I will announce it here.

Also, what about rain? While I don't like riding in the rain, I don't think it slows me down at all, unless it gets heavy, in which case, I usually stop under something to wait for it to abate or cut my day short just to get out of the rain.

Thanks,

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Old 10-30-09, 11:45 AM   #2
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well you can hide from the rain but wind is going to slow you down bigtime especally strong cross headwind, combine the two and it's a good case for selling the lot.
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Old 10-30-09, 11:46 AM   #3
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Have you looked at this?

http://www.noping.net/english/
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Old 10-30-09, 11:50 AM   #4
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its not linear. go on one of the power to speed calculators and assume like 100 or 150 watts or just take their formula and let the user input their speed.
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Old 10-30-09, 11:51 AM   #5
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Wind plays a HUGE part in touring. Wind plays a big enough part in recreation and racing cycling that it is annoying. But when you are touring with panniers and rolls and packs full of stuff, they almost act as a sail.

Strong headwinds can cut your mileage down by almost half if it is bad and consistent. Tailwinds can help you fly.
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Old 10-30-09, 01:02 PM   #6
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All I know is if it's behind me I'm fast and if it's in front of me I'm slow.
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Old 10-30-09, 02:11 PM   #7
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I remember reading, probably in a racing context, that at 25 mph 80% of your resistance is from the wind. Double you speed resistance goes up 4 times.
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Old 10-30-09, 02:26 PM   #8
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Are you talking about the kind of wind that exists all the time when you are not moving or are you talking about air resistance because of how fast you are going?

Basically if you take a reference frame that moves with the bicycle, the amount of resistance that you get will increase exponentially with the relative speed of the air against your direction of travel. So travelling at 15 mph plus a 20 mph crosswind coming in at 2 o'clock will give you a total head on air speed of 25 mph. Thus you will have to work the same amount as if you were going 25 mph with no wind just to maintain your speed of 15 mph. This is equal to 2.8 times more power. Not fun.
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Old 10-30-09, 03:04 PM   #9
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Wind, rain, weight and all the rest of it rarely affect distance. What they may affect, however, is time.

If you've got a strong headwind, you may arrive at your destination 2 hours later than you would if you had a tailwind. But you'll have covered the same distance.
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Old 10-30-09, 03:32 PM   #10
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Quote:
Originally Posted by raybo View Post

Also, what about rain? While I don't like riding in the rain, I don't think it slows me down at all, unless it gets heavy, in which case, I usually stop under something to wait for it to abate or cut my day short just to get out of the rain.
If it rains, and your clothing gets soaked, you can wring out the clothing into one of your water bottles. That transfers the weight from your clothing onto the bike.

And since we all "know" (based on prior threads) that weight doesn't affect speed on a touring bike this will actually speed you up by moving the weight from a place where it matters (your body) to a place where it doesn't (your bike).

Of course, this raises the question -- what do you do with the water that was in your water bottle before you wring out your wet clothes? If you drink it, it will make your body heavier, thus negating the impact of transfering the water from your clothes to the bike. Better if you pour the water from your water bottle out on the ground before filling it with rain water.

Just a tip. I hope I have my math right on this.
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Old 10-30-09, 03:36 PM   #11
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Wind, rain, weight and all the rest of it rarely affect distance. What they may affect, however, is time.

If you've got a strong headwind, you may arrive at your destination 2 hours later than you would if you had a tailwind. But you'll have covered the same distance.
If you are free camping, expedition touring etc; it will affect distance rather than time, as there is no need to hit a daily mileage mark. By the time it hits 5pm, you'll likely start looking for a place to pitch, regardless of distance travelled.
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Old 10-30-09, 04:18 PM   #12
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Here is the formula:

d = one over the fourth root of wind speed times average cycling speed less f(r).
Where r is rage measured in kilojoules.
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Old 10-31-09, 08:13 AM   #13
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Can someone do a comparison between headwinds and inclines. If I think about the gear I'm in climbing a 6% slope and the gear I'm in pushing forward in a 15mph cross headwind they seems about the same. Also, 11% grade might compare to a 20mph? Just guessing and wondering. Thanks
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Old 10-31-09, 08:35 AM   #14
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Can someone do a comparison between headwinds and inclines. If I think about the gear I'm in climbing a 6% slope and the gear I'm in pushing forward in a 15mph cross headwind they seems about the same. Also, 11% grade might compare to a 20mph? Just guessing and wondering. Thanks
But climbing is like putting money in the bank, fighting wind is just losing money (unless you get to take the same route back to where you started)
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Old 10-31-09, 09:20 AM   #15
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Here is the formula:

d = one over the fourth root of wind speed times average cycling speed less f(r).
Where r is rage measured in kilojoules.
In the words of Chevy (Gerald Ford) Chase,

"I was told there would be no math on this forum"
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Old 10-31-09, 02:11 PM   #16
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I think the wind really blows...
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Old 10-31-09, 02:30 PM   #17
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On a windless day on gentle terrain on a loaded bike, I'll usually average about 19-20kph (not fast but hey the engine was built in the 50s). With a headwind of say 20kmh, I slow to maybe 13kmh. With the same tailwind I'd speed up to about 26kmh. When the headwind is like a gale, say 50kmh, it's like riding up a steep hill and my speed might drop to as little as 7kmh (zero if I can find some place to stop).

So for me anyway, dividing the wind speed by about four gives the speed effect. In terms of distance, if I cycle for five hours a day into a 20kmh headwind, my distance would drop from 100km to 65km or so.

As Machka implies, you may decide to put in some extra hours to make up for the headwind's effect but, if anything, I would be inclined to hope the wind is better the next day and cut the hours back a little.

Regarding rain, I'd generally slow by about 10% on the flats when the road is slippery, 25% on steep descents, no change on ascents.
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Old 10-31-09, 03:50 PM   #18
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If I were to guess - people approach an incline more favorably than a headwind. Becuase the incline has a known end? Its all resistance.

Thanks for the groovy formula, I was trying to find out if anyone had thought of mph in terms of % gradient. Hills and mountians don't bother me all that much, I guess becuase I'm used to pushing against a wind. Just wondering if anyone had a firm concept on the comparison.
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Old 10-31-09, 11:35 PM   #19
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If you've got a strong headwind, you may arrive at your destination 2 hours later than you would if you had a tailwind. But you'll have covered the same distance.
A strong enough wind can affect distance as well. In New Zealand I rode into winds so strong that sustaining 11km/h on the flat was hard work. I remember riding over a steep mountain pass, and descending the other side without changing gears, cadence or speed because of the strength of the wind. Alternatively, I've had tailwinds that allowed me to holler along at almost 40km/h without even pedalling.

Here's another question: How many consecutive days have you been riding into said headwind? I can put my head down spend some extra time in the saddle for a while, but if it's a week of relentless headwinds, I'll start shortening the distances.
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Old 11-01-09, 03:01 AM   #20
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If I were to guess - people approach an incline more favorably than a headwind. Becuase the incline has a known end? Its all resistance.
I prefer to fight gravity over fighting wind for sure, but not so sure about why. Maybe this "known end" idea, or maybe Dan the Man`s "bank" idea. Here`s another maybe- maybe because hills are fair. They`re always there, always the same. They don`t suddenly change their slope to the other direction so that you have to struggle up in both directions unless you`re Bill Cosby. Climbs usually pay off in views, too.

Another personal observation about wind and grades is that headwinds bother me more on downgrades than on upgrades. I expect going up to be work, but wind takes the fun out of comming back down again if it`s a small ring struggle.
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Old 11-01-09, 03:06 AM   #21
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If there were truly relentless headwinds, I'd seriously consider altering my plans -- either bus/train/hitch to the destination if it was that important, or turn around and head off to other locales.

I have to say that I haven't had real issues with consecutive days of headwinds. There are several adventures that stand out -- a two-day ride to the start of a fleche in Tasmania, riding along a **** in Holland next to the North Sea for a day, and returning to Dunquerque in 2007 after PBP with another North Sea-generated headwind. The worst was on the Nullarbor in 1997 and on one day, I packed it in after doing only around 40km; the winds started to bug me for a couple of days then, but I got through it.
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Old 11-01-09, 07:13 AM   #22
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The ideal way to approach it is to go to one of the power calculator websites, figure your power output under some "standard" condition, then just that same power combined with a headwind to find your speed under those conditions.

I find for myself that I wind up working harder going into a headwind, though, I don't necessarily keep the same power output.

Also, I don't think the online power calculators allow for baggage on a bike.
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Old 11-02-09, 05:49 AM   #23
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Hi,

Wind kann influence your distance from 0 - 300(+) km. I never know how fast the wind is. In Luderritz it was about 120-140, the sandstorm in the Sahara (sidewind) reduced my speed to 5 km/h.

On tour I'm faster when it rains: Nothing to see, less stops -> reach my final destination asap. When it rains I'm cycling - not cruising (what I normally make on tour)

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