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Cyclists in the Race Across America complain about crosswinds, not only because of unpleasant nasal effects...
but also because of a perceived kinetic energy penalty. Does a crosswind actually steal energy from a cyclist?
Represent the cyclist and bike as a frictionless cart on a track. The cart has the same drag coefficient for any direction of incident wind. It travels at 20 mph along the track and there is a 20 mph crosswind. (To be clear, the crosswind is perpendicular to the track, and the apparent wind felt by the cart is 45 degrees off straight ahead.) State your case for or against additional drag loss due to the crosswind.
gilbert, this isn't an answer, it's part of my question!
achillesfear, the PATH isn't into the wind, only the attitude. And it's debatable whether the biker crabs his attitude like a plane, even slightly. This would require tire scrub to stay on course, which is where the energy would go. My experience is that I just lean the bike. Anyway, I'm looking for something more fundamental, which is why I asked that you idealize the bike and cyclist as a cart (which can't sideslip or get pushed off the track).
hec, the answer is indeed in the aerodynamics, and the loss of drafting is a good thought. But RAAM riders tend to be loners, at least for most of the long cross-country trip. Maybe I could have been clearer, but I did refer to "the cyclist" and "a cart", and I'm looking for something that affects the single rider.
I hope you and the other answerers feel free to edit their answers if still interested. Here's a hint: Do the math.
melancholygiant, leaning may put you in a suboptimal position making the production of energy less efficient and comfortable (though in a steady crosswind, veteran bikers do a rigid lean, keeping the same relation to the bike). But your argument for more muscular energy is not solid. I asked for a yes or no on more drag force on an inanimate cart, and some math is needed.
This is about the decision below (they only give you 300 characters there). Here is what I was looking for:
Definitions
Vectors, Vw incident wind velocity, Fw air resistance aligned wih Vw
Fw(x) is aligned with motion
|A| is magnitude(A), A/|A| is unit vector along A
Aerodynamics says Fw=K * |Vw|^2 * Vw/|Vw|
Results
No xwind: Vw=[20,0], |Vw|^2=400, Fw=K*[400,0], Fw(x)=400
With xwind: Vw=[20,20], |Vw|^2=800, Fw= K*[566,566], Fw(x)=566
So there's a 41% drag penalty due to the crosswind.
Well, math may be math, but intuition says the Y force should have no effect since it's at right angles to the cart's velocity. But maybe one can appease intuition as follows: Consider a vertical cylinder moving along X. In a given time interval, the crosswind extends the path the cart cuts through the air by a factor of sqrt(2), while the path's width remains the same. So the mass of air subjected to an X-axis momentum change by the cart's passage is also scaled by sqrt(2). That works for me.
5 Answers
- hecLv 52 decades agoFavorite Answer
I think the answer lies not in mechanics, but in aerodynamics and maybe the theory of turbulence. My initial answer was that they will need additional energy to keep the bicycle stable, which might be true. Then I had an additional idea. I guess you are talking about cyclists moving in a group, not single cyclists. This group creates an air pocket (aerodynamic shade) which moves together with them, making cycling easier for those who cycle inside the group. Cross-wind blows this pocket away (or changes its shape dramatically), thus making it harder, especially if you have gusts of wind. I would conjecture that if the road were wide enough and the cross-wind is steady, the group would still be able to benefit from the aerodynamic shade.
- Anonymous2 decades ago
Represent the cyclist and bike as a frictionless cart on a track. The cart has the same drag coefficient for any direction of incident wind. It travels at 20 mph along the track and there is a 20 mph crosswind. (To be clear, the crosswind is perpendicular to the track, and the apparent wind felt by the cart is 45 degrees off straight ahead.) State your case for or against additional drag loss due to the crosswind
- Anonymous2 decades ago
I agree with achilles.
I'm no aerodynamic engineer, or physicist, but, with my rudimentary understanding of physics, I would say that the crosswind does not create any additional drag compared to no wind. However, it does apply a force to the rider perpendicular to the rider's forward momentum/inertia. A 20 mph crosswind would require the rider to expend energy to create an equal counterbalancing force to maintain a straight path, thus expending additional energy not required in a no wind situation.
Even though the bike can't be "blown off course" like an aircraft, energy must still be expended to keep it upright enough to maintain a steady course. Leaning requires energy to be expended by your muscles that is not spent when there is no crosswind.
Sorry, since I haven't taken Physics since high school, I've forgotten the Math.
- 2 decades ago
Ok... If you think of an airplane then what the pilot has to do is alter their course such that they are still able to get to where they wanted to despite the crosswind so to a degree they have to fly into the wind to get to where they want to go.
Now if you think of a bicycle then they can't adjust their course that much so what they have to do is work to keep the bicycle going straight. If you travel in a straight line and you have the cross wind and you don't correct for it then you will end up pushed off the track. You're losing kenetic energy by fighting the cross wind to stay in position because to maintain a straight path you have to slightly adjust to make the path somewhat into the wind.
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- Anonymous4 years ago
21 minutes to jog a mile? No offense yet this is undesirable. At your age, you should be waiting to run a mile in between 7-10 minutes. on the optimum, you should job the mile at around 12-quarter-hour. additionally, develop your %. by way of fact the two.6 on my elliptical is extra of a rapid walk.
