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Old 07-14-06, 09:23 PM   #1
RockyMtnMerlin
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How wind and climbing affect average MPH

Today's ride. 66 miles round trip. About 2100 feet of climbing almost all of that on the way out. 15.4 MPH out into a variable cross head wind sometimes up to 17 mph. 23.4 mph on the way back. To state the obvious........ downhill with tail wind does not make up for uphill with head wind. At the 23 mile point going up an 8% grade at 7 mph with a stiff head wind I thought about turning around. But within 2 miles the wind went down so I continued on. Soft drink and chips fueled me on the way back (in addition to the 2 Power Bars {one consumed just before start** and 4 servings of Hammer Gel on the round trip). Elevations 7100 to 8400 feet.
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Old 07-15-06, 01:02 AM   #2
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Originally Posted by RockyMtnMerlin
......... To state the obvious........ downhill with tail wind does not make up for uphill with head wind. .

Ah...the pilot's dilemna. The reasons are obvious. Given an identical wind on nose going out and wind on nose coming back, you spend more time at the slower speed. Works the same with a bike.
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Old 07-15-06, 01:24 AM   #3
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Originally Posted by Monoborracho
The reasons are obvious. Given an identical wind on nose going out and wind on nose coming back, you spend more time at the slower speed.
Exactly how is that obvious, and what drugs are you taking to make them so???
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Old 07-15-06, 06:29 AM   #4
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Monoborracho is correct! This is a common point of discussion in aviation. A good problem to give student pilots to calculate out with their computers when they don't believe this bit of trivia!
Assuming your "cruising speed" is the same both ways, your "ground" speed is greater going downwind and less going upwind, so you spend more time in the slower mode and less time in the faster mode to cover the same distance, so going upwind always takes longer than than the reverse course. Same thing when going uphill on a bike or climbing to altitude in a plane.
If I were a Native American I'm sure my Indian name would be, while biking or flying, "Wind On The Nose!"
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Old 07-15-06, 11:30 AM   #5
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Originally Posted by bobkat
Assuming your "cruising speed" (=energy or power expended when bicycling) is the same both ways, your "ground" speed is greater going downwind and less going upwind, so you spend more time in the slower mode and less time in the faster mode to cover the same distance, so going upwind always takes longer than than the reverse course. Same thing when going uphill on a bike or climbing to altitude in a plane.
If I were a Native American I'm sure my Indian name would be, while biking or flying, "Wind On The Nose!"
My nickname is "Pedal Uphill with Wind on the Nose"

Actually, my first revelation of this problem was, as you said in your post, during undergraduate pilot training.

"........and then the wheels came off"

Last edited by Monoborracho; 07-15-06 at 11:40 AM.
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Old 07-15-06, 11:37 AM   #6
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Exactly how is that obvious, and what drugs are you taking to make them so???

1) It is intuitively obvious to the most casual observer.

2) You spend more time at the slower speed.

3) Here's a story problem for a 20 mile out roundtrip. If you can make 20 mph going downhill with the wind, it will take 1/2 hour to cover 10 miles. If you can make only 10 mph on the back trip it will take one hour to get home. Average speed, 20 miles divided by 1.5 hours = 13.667 mph. Doesn't quite work out does it? You will not average 15mph on the trip.

4) See statement 1) above.
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Old 07-15-06, 05:02 PM   #7
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Monoborracho is correct. The problem with wind (or hills) is that in order for a tailwind to cancel out a headwind you have to average over time, but with any round trip you are averaging over distance.

Consider a twenty mile out and back round trip that you can do in exactly one hour with no wind (a 20 mph average speed obviously). One particularly windy day you set out into a terrible headwind. You can only maintain 10 miles per hour. The trip out will take one hour. There is no way you can average 20 mph for the whole trip now. You could go one thousand miles an hour on the way back and it would still take over an hour for the whole trip.

However, let's say after you make the turn around you can hold 30 miles an hour on the way back. If you were to maintain this speed for one hour (the same amount of time you spent on the way out) you would have covered a total of 40 miles (10 out and 30 back) in two hours for an average speed of 20 miles per hour, the same as you do with no wind. This is averaging over time.

This is the way it would work with a plane, but a bike has an additional reason why a wind will slow your average speed. The rolling resistance of a bike goes up as the speed increases regardless of what way the wind is blowing. The bearings in the wheels, wind resistance of the spokes, and friction of the tires on the road will mean that you won't be able to maintain 30 mph on the way back, maybe only about 28-29 mph. This means that even if you did spend one hour riding into the wind and one hour riding with the wind, you would probably come up slightly short of your average speed with no wind.
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Old 07-15-06, 05:18 PM   #8
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Experience has taught me that there are more points on the compass where wind inhibits you than where it speeds you.
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Old 07-15-06, 05:24 PM   #9
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Doesn't all that gel stuff give you the runs? It rips me up...
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Old 07-15-06, 06:10 PM   #10
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I am convinced that the wind always changes direction coincident to my riding path. If I fight a headwind on my way out, it always seems to manage to have shifted so that I have to fight it on my way back, also. Bummer.

Caruso
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Old 07-15-06, 08:14 PM   #11
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Doesn't all that gel stuff give you the runs? It rips me up...
Nope. In my Navy career I lived in Spain, Korea and Germany and visitied about 30 other countries. The only place I have (or had) stomach problems is in Mexico. Except for that, I have an iron clad stomach (and lower GI tract) FWIW, the only gel I have ever used is Hammer Gel. Perhaps that is the reason that it does not bother me.
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Old 07-15-06, 08:16 PM   #12
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Originally Posted by Carusoswi
I am convinced that the wind always changes direction coincident to my riding path. If I fight a headwind on my way out, it always seems to manage to have shifted so that I have to fight it on my way back, also. Bummer.

Caruso
I actually saw a study that tested folks on bicycles and they perceived a headwind through an arc of nearly 230 degrees of wind direction. Of course that can't be right but that is what they felt.
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Old 07-15-06, 08:32 PM   #13
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Merliln you are probably correct. Another aviation tidbit. In order to have a tailwind component (to help push you) you need a wind at least 10 degrees behind you, as a direct crosswind will still slow you down as you have to tack into it to maintain the correct forward direction. I suppose the same factors are at work with bikes, too.
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