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  1. #1
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    Headwind/tailwind average out??

    If you ride directly into a 10MPH head wind 15 miles, and then do the same with a tail wind for 15 miles, do you get the same average of zero wind when you ride??
    It seems I don't and the head wind takes out of my average. What about you?
    Last edited by schmalts; 05-05-2009 at 05:15 PM.

  2. #2
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    Wind makes you lose. Unless you can ride with the wind for the whole ride.....
    Just ride.

  3. #3
    jaydub_u
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    I was wondering the same thing as I went on my 20 mile loop and when I started out I thought that all was good and I was tooling along at my normal pace and actually thought I was doing better. Hovering around 18 to 20 mph. Usually I run the loop at about a 17.5mph average. Well coming back I thought it was kinda brutal and then it started to rain. Got back to the car and my avg. said 15.4. And I felt like I did 40 miles.

  4. #4
    duh...
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    Quote Originally Posted by mikagsd
    Fat tire Fred....you are the bike god of the universe and unless someone agrees with your reasoning they are just plain stupid

  5. #5
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    Last Saturday and Sunday I did my usual 20 miles out and 20 miles back ride. BOTH days the wind switched around, I had a head wind out and then a head wind back in and only averaged 14.5. Today I got the MTB out and got into quite a bit of mud...I've never ridden into a head wind on the road that offered THAT kind of resistance!

  6. #6
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    The other day I had a tailwind that allowed me to hit 30mph on a flat without even pushing hard. That's completely unrelated to your discussion, just thought it was a fun fact.

  7. #7
    Cpark
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    Quote Originally Posted by schmalts
    If you ride directly into a 10MPH head wind 15 miles, and then do the same with a tail wind for 15 miles, do you get the same average of zero wind when you ride??
    It seems I don't and the head wind takes out of my average. What about you?
    I think it does as long as the terrain is flat.
    I'm thinking if you are climbing and face headwind then it may not affect the wind resistence that much due to lower climbing speed?
    Maybe some physicist in RBR forum can chime in for some scientific analysis.
    Last edited by cpark; 05-05-2009 at 08:09 PM.

  8. #8
    jains89
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    You will have a lower average speed if there is wind. Just like climbing uphill, you will spend more "time" at the slower speed even though it's the same distance, therefore it has a greater affect on the average.

  9. #9
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    I once manipulated my ride so that I was out of the wind, until this long 8 mile stretch home. The tailwind made me average 28mph on the way back. I felt like Lance!

    Usually, though, if there's a headwind, it's some sort of Murphy's Law that it'll shift, and be a headwind on the way back too.

    Also, Jains89 is right. You spend more time at the lower speed. Like the way tooling around the parking lot seems to drop a full 1mph off the average, and then you'll spend a whole ride getting it back.

  10. #10
    eRacer
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    Why does it seem to be uphill and against the wind; in both directions?
    John Lapoint / San Diego
    God is Great, Beer is Good, and People are Crazy!

  11. #11
    Frog Whisperer
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    note....it is miles per HOUR,....all about TIME.....just like Jains89 said!...so no....besides the wind is almost NEVER directly at MY back......
    Of course I'm sure...that doesn't mean I'm right......

  12. #12
    wim
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    There is one way for a tailwind to make up for a headwind average speed loss: ride for a certain amount of time into a headwind, then turn around and ride for the same amount of time with a tailwind. Of course, you'll wind up way past your starting point . . .

  13. #13
    Frog Whisperer
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    Quote Originally Posted by wim
    There is one way for a tailwind to make up for a headwind average speed loss: ride for a certain amount of time into a headwind, then turn around and ride for the same amount of time with a tailwind. Of course, you'll wind up way past your starting point . . .
    yeah but THEN you have to turn around, and ride BACK INTO the wind to get home.....guess how I figured that out?

    a month ago I god 20 with a 20 to 30 mph tailwind and my fife picked me up......SWEEEEEEEEEEEEEET

    only time it got a bit dicey was when I had to cross the wind......a 30 mph cross wind is scary.
    Of course I'm sure...that doesn't mean I'm right......

  14. #14
    RoadBikeReview Member
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    a little math example

    A hypothetical: Imagine a headwind that slows you down to half the speed you'd normally go at a given effort. When you turn around, the tailwind would have to propel you at infinite speed to make up the difference -- you'd have to get back in no time at all. So wind will slow you down on average.

    Same thing applies to climbing. You take more extra time on the climbs than you can make up on the descents. But it's actually worse with the wind, because of one more factor. Wind resistance increases (generally) in an exponential fashion. If you go twice as fast (or have twice as strong a headwind), you have (roughly) 4 times the wind resistance. So the higher relative wind speed with the headwind will have more effect on your speed than the drop in wind resistance you get with the tailwind.

    And one more point. You very rarely actually get "pushed" by a tailwind. For that to happen you'd have to have a wind faster than your riding speed. Doesn't happen often. What you get is lower wind resistance, because the relative "headwind" is slower -- which does have a real effect.

  15. #15
    Master debator.
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    Quote Originally Posted by Ricko
    Last Saturday and Sunday I did my usual 20 miles out and 20 miles back ride. BOTH days the wind switched around, I had a head wind out and then a head wind back in and only averaged 14.5. Today I got the MTB out and got into quite a bit of mud...I've never ridden into a head wind on the road that offered THAT kind of resistance!
    I hate that. I've spent 35 miles fighting a horrible headwind, thinking it'll be great on the way back. Then you turn around and find it's still more or less at your face again, and it makes you want to scream out loud when you look at your speed.

    On the plus side, it's great training. Look at you heart rate while pushing into the wind versus going with the wind.

  16. #16
    RoadBikeReview Member
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    Cross winds feel much more like head winds than like tail winds, too.
    We have nothing to lube but our chains.

  17. #17
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    Quote Originally Posted by schmalts
    If you ride directly into a 10MPH head wind 15 miles, and then do the same with a tail wind for 15 miles, do you get the same average of zero wind when you ride??
    It seems I don't and the head wind takes out of my average. What about you?
    Pretty basic elementary school question...
    No they do not "even out".... you spend much more time biking into the headwind than the tailwind.

    Lets say Joe rides into a headwind at 15mph for 1 hour, then turns home. On the way home, he can ride at 30mph. Therefore his average speed is 30 miles/1.5 hours = 20mph average... just 5mph faster than his "headwind" speed (if the wind "evened out" his avg speed would be 22.5 mph. And my guess is that averaging 30mph for 15 miles is quite generous.

    The same idea can be applied to hills. If you climb a 10 mile long mountain in 1 hour, but you get to descend down at 40 mph, will your average speed be 25mph... answer, no.
    20 miles / 1.25 hrs = 16 mph average. The rider probably would have a higher average speed if he did not climb the mountain (same idea applies to wind, no wind = faster average speed).

    Also note, that the forces of wind for or against a rider are squared and therefore grow exponentially as wind speed increases. In the case of a tailwind, a good scenario would be for 0 net wind resistance, but the overall average speed still suffers.

  18. #18
    n00bsauce
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    Quote Originally Posted by schmalts
    If you ride directly into a 10MPH head wind 15 miles, and then do the same with a tail wind for 15 miles, do you get the same average of zero wind when you ride??
    It seems I don't and the head wind takes out of my average. What about you?
    You lose a lot more from going into a head wind than you gain from going with a tail wind.
    "Those who can make you believe absurdities can make you commit atrocities." Voltaire

    There are your fog people & your sun people, he said. I said I wasn't sure which kind I was. He nodded. Fog'll do that to you, he said.

    "We are all ignorant about most things."
    Mel Erickson

  19. #19
    Roadie with unshaven legs
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    Quote Originally Posted by Ricko
    Last Saturday and Sunday I did my usual 20 miles out and 20 miles back ride. BOTH days the wind switched around, I had a head wind out and then a head wind back in and only averaged 14.5. Today I got the MTB out and got into quite a bit of mud...I've never ridden into a head wind on the road that offered THAT kind of resistance!
    This is a phenomenon that I have had plenty of saddle time to mull over. Let's say that you are riding into an 8 MPH headwind at 12 MPH average. The speed differential of the wind hitting you in the face is about 20 MPH. When you turn around and head back the way you came that same headwind is now an 8 MPH tail wind. It's not pushing you along but you still feel wind blowing from in front of you but now you are riding along at more like 18 or 20 MPH, the speed differential is 10-12 MPH in your face. Can you tell the difference between a 20 MPH and a 10 MPH wind hitting you in the face? The way to tell is to slow down until it feels like you are riding in still air and note the speed that you are going. Since you are riding at the same speed the wind is blowing in the same direction as the wind you will feel like the air is not moving at all.

  20. #20
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    you can always just use the formula ;)
    W = work done (necessary) by rider, in watts
    Cfriction = coefficient of friction of bike over ground (0.1 is a general estimate)
    V = velocity (in meters/second)
    P = weight of rider (in kg)
    Vwind = wind velocity (in meters/second)
    Cslope = slope coefficient
    Slope% = slope of road in percent
    Acceleration can be 0 if you assume a constant rate.

    W = Cfriction x V x P + Cair x (V + Vwind)^2 x V+ Cslope x P x Slope% x V + acceleration

    assuming you want to keep your power output consistent through the whole ride, you can solve for V with different Vwind configurations.

    You can also solve for the Watts needed to overcome air resistance:

    Wair = Cair x (V + Vwind)^2 x V

    Velocity calculations in meters/sec
    where Cair (coefficient of air friction):
    = 0.7 MTB, loaded hybrid bike
    = 0.45 for a hybrid, or perhaps upright road bike position (sitting up)
    = 0.36 for road bike
    Certainly these are estimates. If you want the exact number, schedule an appointment in the wind tunnel. Hopefully they have an appointment open between L.Armstrong and L.Leipheimer.

  21. #21
    Resident Curmudgeon
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    That made my head hurt.
    Don't believe everything you think.

  22. #22
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    I think I stopped reading back at:

    "If train A travels West from Chicago @ 15 mph and train B travels East from Seatle @ 25 mph, what time is lunch in Tuscon?"

    But seriously, to the OP's question - I say NO, 'cause there's a tendency to push too hard into the headwind (try to maintain pace.) When you turn around you're more spent & your "tailwind" pace suffers. Hence your overal ave is degraded when it's windy. At least so it seems for me.

  23. #23
    Slippery Old Devil
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    Rode a 200K brevet April 25th. 25 mph head and cross wind for 86 miles. When I finally got the wind behind me I had long since been cooked. I managed to sit at 24-27 mph for a while but, in the end, I averaged only 12.8 mph over the whole 200K.

    "That was, without a doubt, my worst day on a bike." Lance Armstrong in the 2000 Tour after he'd been dragged through the Alps for three days by Marco Pantani.

  24. #24
    jaydub_u
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    Quote Originally Posted by oily666
    Rode a 200K brevet April 25th. 25 mph head and cross wind for 86 miles. When I finally got the wind behind me I had long since been cooked. I managed to sit at 24-27 mph for a while but, in the end, I averaged only 12.8 mph over the whole 200K.

    "That was, without a doubt, my worst day on a bike." Lance Armstrong in the 2000 Tour after he'd been dragged through the Alps for three days by Marco Pantani.
    Good for you and your gut check. Forget the avg. mph. That wind is some tough stuff. I did a 30 mile loop today and avg. 18mph on the way up the hill and with a tailwind for the first 15 and on the way back, down hill I avg. 17mph with about a 10mph head wind.

  25. #25
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    I usually seem to end up with a headwind both ways (grr...)

    To put into words the earlier formula: Air resistance has a component which goes up with the square of airspeed, and one which goes up linearly with airspeed. The linear component cancels in the out-and-back scenario, but the squared component continues to get greater with greater wind speed.

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