compare head wind with climbing?
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  1. #1
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    compare head wind with climbing?

    hello everyone

    if I ride on a flat road into ~20 miles/per/hour headwind (~32kmh) how many degrees of gradient does it compare to, approximately? I am just looking for basic approximations, in absense of any hard data.

    thanks

  2. #2
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    i used this:
    http://analyticcycling.com/ForcesSource_Page.html

    and according to it... riding at 15mph directly into a 20 mph wind looks like this:

    Standard (gmf) % Test (gmf) %
    Total Force on Rider 4598.7 6602.0
    Wind Resitance 3825.1 83.2 5609.6 85.0
    Rolling Resistance 304.5 6.6 304.5 4.6
    Gravity Force 0.0 0.0 0.0 0.0
    Drag on Front Wheel 268.0 5.8 393.1 6.0
    Drag on Rear Wheel 201.0 4.4 294.8 4.5

    Riding up a 6% grade looks like this:
    Standard (gmf) % Test (gmf) %
    Total Force on Rider 5659.7 6627.2
    Wind Resitance 702.0 12.4 1563.8 23.6
    Rolling Resistance 304.5 5.4 304.5 4.6
    Gravity Force 4567.2 80.7 4567.2 68.9
    Drag on Front Wheel 49.2 0.9 109.6 1.7
    Drag on Rear Wheel 36.9 0.7 82.2 1.2

    therefore the answer is: a little less than 6% at 15mph, weighing what the "dummy" weighs...

  3. #3

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    The hard part about that equation is that wind resistance is a function of the cube of the wind speed (to the power of 3) Thus, the resistance is less if you are riding at 10 mph into the wind compared to 20 mph into the wind. The resistance added by a gradient is constant regardless of how fast you are going.

    That being said, I would throw out that a 20 mph wind at 15 mph riding speed is like a 5% grade. That is not based on anything scientific, just recollection of a few rides. (However, I am an estimator by trade and I did stay at a Holiday Inn Express last night)

    Edit: Judging from the post that just beat me in, my estimate was about right. I was thinking 6% but knew that was too much.

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    thanks

    thank you both. How much did the dummy weigh?

    I weigh ~150# and I was averaging ~23kmh into ~35kmh head wind for ~18km distance. Sounds like ~4% gradient?

  5. #5
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    Realize that different muscles are used during a climb than while on the flats. Also, you can always tuck to get more aerodynamic, but you can't ride through a hill

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    Quote Originally Posted by 99trek5200
    The hard part about that equation is that wind resistance is a function of the cube of the wind speed (to the power of 3) Thus, the resistance is less if you are riding at 10 mph into the wind compared to 20 mph into the wind. The resistance added by a gradient is constant regardless of how fast you are going.

    That being said, I would throw out that a 20 mph wind at 15 mph riding speed is like a 5% grade. That is not based on anything scientific, just recollection of a few rides. (However, I am an estimator by trade and I did stay at a Holiday Inn Express last night)

    Edit: Judging from the post that just beat me in, my estimate was about right. I was thinking 6% but knew that was too much.
    Drag (or wind resistance) is proportional to velocity squared (as long as you aren't in a Stokesian environment ). Required power to overcome drag is proportional to velocity cubed.

    Resistance going up a hill (neglecting wind resistance) is independent of speed. Power required to go up a hill is thereforemerely proportional to velocity.

  7. #7
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    I'd rather climb a steep hill than ride into a strong wind anyday, but there have been many times I've climbed steep hills into a very strong wind. Wind does blow down hill! And it is often very windy on mountains.

  8. #8
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    If only you could get to the top of a headwind.

    Well, I guess you can turn around...

  9. #9
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    This is only true.......

    Quote Originally Posted by iliveonnitro
    Realize that different muscles are used during a climb than while on the flats. Also, you can always tuck to get more aerodynamic, but you can't ride through a hill
    if you are climbing out of the saddle. Which BTW is one of the things that makes hill climbing easier.....you can rest ione set of muscles (seated climbing) by using a different technique (standing climbing. Can't do that into a headwind. In addition, you get to rest downhill on a climbing course........with a headwind, no resst at all until you turn to come home.

    Len



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  10. #10
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    Quote Originally Posted by walrus
    I'd rather climb a steep hill than ride into a strong wind anyday
    +1 Even though the effort feels about the same, there's a whole lot more satisfaction getting up a hill than there is pounding into the wind. And I'm tall, so headwinds make for extra suckage.

    About the only time I like a headwind is when it's >100 deg F and humid. Luckily, those days should be behind us until next year.
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  11. #11
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    Hills versus wind -- it's like the devil that you know versus the devil that you don't know. I will leave the physics to others. But, I will take hills any day over wind. At least with a hill, you know how long and how high it is. With the wind, you never know how long it is going to last and it can change without warning. And, as the song from the '60s goes: "What goes up must come down." However, when it comes to wind, it seems like it almost always is blowing in my face. I sometimes doubt that tailwinds actually exist.
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    A 150lb rider riding in the drops will need 333 watts to go 15mph in a 20mph wind. The same rider will need 349 watts to go up a 5% grade. However, if the rider is riding on the tops he would require 475 watts which would be like a 7% grade. For riding into the wind how aero you ride makes the most difference, for hills your body weight makes the most difference.

  13. #13
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    Great thread, I have been wondering that for a while. I live in the great flat lands of South Florida. One of the rides I do is always like 8 miles into a head wind with no protection from the wind, how I hate the section of the ride.

  14. #14
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    acid_rider: I weigh ~150# and I was averaging ~23kmh into ~35kmh head wind for ~18km distance. Sounds like ~4% gradient?

    Are you sure you can hold 23 km/hr into a 35 km/hr headwind for 45 minutes? As mentioned above, this means you can hold 330-340 watts over that time which is absolutley outstanding. As in Cat 1 outstanding!
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  15. #15
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    Of course, 15mph up a nearly 6% grade isn't bad for a mile or so, but to sustain that effort over 10-20+ miles of headwind would be alot of work. At that distance I bet a much more sustainable speed in that much wind is more like 10-12 mph... but that's just recreational me...

  16. #16
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    Quote Originally Posted by Len J
    ...with a headwind, no resst at all until you turn to come home.
    At which point, the wind magically shifts direction, leaving you speechless in disbelieving frustration (except for the 4-letter words, of course).
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  17. #17
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    no, I am lousy, actually

    Quote Originally Posted by serious
    acid_rider: I weigh ~150# and I was averaging ~23kmh into ~35kmh head wind for ~18km distance. Sounds like ~4% gradient?

    Are you sure you can hold 23 km/hr into a 35 km/hr headwind for 45 minutes? As mentioned above, this means you can hold 330-340 watts over that time which is absolutley outstanding. As in Cat 1 outstanding!
    I am lousy. No Cat anything.

    the wind was ranging from 30kmh to gusts of 40kmh (weather station nearby) and the direction was ranging from head-on to ~45 degree angle (it felt like) so I suspect I was nowhere near as good! I would be happy with Cat-4 performance (is there such a thing?). I am but a humble fitness rider so there is no way I can pump out that much power. The computer said 23kmh average though. I was riding 90% on the tops and brake hoods, not drops. I did pass quite a few riders along the way. What I really hate are cross-winds of >35kmh, for safety reasons, but head wind makes you stronger as done climbing.

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    Missing a key point

    Quote Originally Posted by acid_rider
    if I ride on a flat road into ~20 miles/per/hour headwind (~32kmh) how many degrees of gradient does it compare to, approximately? I am just looking for basic approximations, in absense of any hard data.
    The information provided you so far is factually correct, but everyone is missing a key point. The reported wind velocity that you hear is measured 30 feet (10 meters) or so above the ground, and far away from any buildings, trees, hills, or any other object that would affect the wind speed. The practical realities are that when riding a bike, even in very open country, the wind speed that the bike/rider experience is much less than the reported velocity. If there are any trees, houses, bushes, or even crops along the road, wind speeds are even lower. Plus, the wind speed at ground level is, by definition, zero, so we are always riding in a diminished wind space. IME, from knowing how huge an impact a headwind would have in a "wind tunnel" space, I would say that the actual winds we experience as riders are something like 1/4 to 1/3 of the reported wind velocity.

    So, for that 20 mph reported headwind, you are more likely seeing 5-7 mph at the bike. All of the numbers you have been given so far do not reflect that, so real world the wind effect is MUCH lower than what has been quoted. It is still huge, but nowhere near as huge as you would believe by plugging headwind speed into analyticcycling, etc.

  19. #19

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    Granted wind varies from one location to another due to the obstructions. Looking at the different weather station locations that www.wunderground.com uses in my area, many have similar obstructions.

    From a ride I took into a strong headwind down the Sacramento Valley, I can tell you it was pretty stiff (15mph+) and it was like a 4-5% grade. I am sure no one was claiming it was 45-60mph.

    In some situations buildings and such can increase wind speed as it creates narrow openings for wind to pass through, thus velocity increases. Think how windy it can be in the concrete canyons of major cities.

  20. #20
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    Comparing wind vs hills also depends on how heavy you are. As everyone knows, heavier cyclists have to work much harder on hills than lighter ones. However, based on my purely anecdotal experience, heavier cyclists seem to hold up better in the wind than lighter ones. I'm not sure about the physics supporting this, but I have observed it time and time again. Some of the best (and lightest) climbers I know absolutely suck when it is windy. And some of the heaviest cyclists I know ride very strong in the wind.

  21. #21
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    Depends on what kind of riding you're doing.

    On a long tour you can put up your tent and wait for the wind to change, but the mountain will be there tomorrow.

    For me, long climbs punish my body; headwinds punish my mind.
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  22. #22
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    Quote Originally Posted by Kerry Irons
    The information provided you so far is factually correct, but everyone is missing a key point. The reported wind velocity that you hear is measured 30 feet (10 meters) or so above the ground, and far away from any buildings, trees, hills, or any other object that would affect the wind speed. The practical realities are that when riding a bike, even in very open country, the wind speed that the bike/rider experience is much less than the reported velocity. If there are any trees, houses, bushes, or even crops along the road, wind speeds are even lower. Plus, the wind speed at ground level is, by definition, zero, so we are always riding in a diminished wind space. IME, from knowing how huge an impact a headwind would have in a "wind tunnel" space, I would say that the actual winds we experience as riders are something like 1/4 to 1/3 of the reported wind velocity.

    So, for that 20 mph reported headwind, you are more likely seeing 5-7 mph at the bike. All of the numbers you have been given so far do not reflect that, so real world the wind effect is MUCH lower than what has been quoted. It is still huge, but nowhere near as huge as you would believe by plugging headwind speed into analyticcycling, etc.
    Surely you have noticed leaves, plastic bags, etc. blowing along the road at speeds as fast or faster than you are riding. Are they able to move faster than the wind blowing them, which you imply is near zero?

  23. #23
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    One more point

    When you're riding into a headwind, you can always just shift into a low gear and rest up for a while (unless, of course, you're racing or some such). When you're on a hill, chances are you're already in one of your lowest gears. Also, if you overcook things on a hill and have to stop, it can be a real pain getting started again. In other words, when you're climbing a hill you really have to gut it through. There's no way of taking a break.
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  24. #24
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    Quote Originally Posted by tarwheel2
    Comparing wind vs hills also depends on how heavy you are. As everyone knows, heavier cyclists have to work much harder on hills than lighter ones. However, based on my purely anecdotal experience, heavier cyclists seem to hold up better in the wind than lighter ones. I'm not sure about the physics supporting this, but I have observed it time and time again. Some of the best (and lightest) climbers I know absolutely suck when it is windy. And some of the heaviest cyclists I know ride very strong in the wind.
    I was thinking along the same lines when this thread started.

    Big guys rule on the flats due to more muscle mass. On the hills they die because climbing is a matter of weight-to-power ratio. I'm lighter (5'11 175 lbs) than some of my riding buddies who are 6'+ 225+ lbs. The bigger guys are able to fight the wind better because of the muscle mass in the their legs. I beat them on the climbs because I have a better weight/power ratio than they do.

    When it comes to wind resistance, surface area plays a bigger factor than weight. Our weight differs greatly, but our frontal surface area does not.

    At least that is my non-scientific theory.

  25. #25
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    Quote Originally Posted by Kerry Irons
    The information provided you so far is factually correct, but everyone is missing a key point. The reported wind velocity that you hear is measured 30 feet (10 meters) or so above the ground, and far away from any buildings, trees, hills, or any other object that would affect the wind speed. The practical realities are that when riding a bike, even in very open country, the wind speed that the bike/rider experience is much less than the reported velocity. If there are any trees, houses, bushes, or even crops along the road, wind speeds are even lower. Plus, the wind speed at ground level is, by definition, zero, so we are always riding in a diminished wind space. IME, from knowing how huge an impact a headwind would have in a "wind tunnel" space, I would say that the actual winds we experience as riders are something like 1/4 to 1/3 of the reported wind velocity.

    So, for that 20 mph reported headwind, you are more likely seeing 5-7 mph at the bike. All of the numbers you have been given so far do not reflect that, so real world the wind effect is MUCH lower than what has been quoted. It is still huge, but nowhere near as huge as you would believe by plugging headwind speed into analyticcycling, etc.
    Unless you're riding through a wind tunnel between buildings. On the start of my commute home, I have a half mile of uphill (a hell of a way to get a warmup!). If the wind is anywhere close to coming out of the south or east, it funnels between some large buildings and an apartment/condo/townhouse complex. From my office on the 8th floor, I can see the wind is barely shaking the trees, so maybe 5mph. But it's probably doing 15 at surface level, coming down that hill, into my face. That part sucks. but once I get on the MUT a few miles later, it becomes a tail wind. Yesterday, I had a fairly consistant 10-15 mph tail wind on the MUT. At one point, I caught a gust, while doing 25 (uphill!!) that actually was blowing faster than I was going. Unfortunately, it then swirlled, and hit me in the face a few seconds later and I was down to 16 or 17 mph. That's what really sucks about the wind. Unpredictable and invisible.
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