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We had a group riding yesterday The max wind speed was 8 m/s

When wind hits you from side direction, I get a feeling chubby riders feels more force from side, than thinner riders.

We were on carbon road or MTB bikes

I wonder my guess is correct?

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  • The really annoying part of cross winds is that they also increase drag in the driving direction. That's a consequence of the drag force growing with the square of your speed. Mar 28, 2022 at 8:01
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    Do you mean 8km/h? That's a light breeze and would be barely felt as a crosswind.
    – Chris H
    Mar 28, 2022 at 10:20
  • Can you define "harder", here? Doesn't the "hit" result from a combination of the wind force and the person/target/victim's surface area? Mar 28, 2022 at 20:12
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    @ChrisH it was 8m/s sorry about that
    – eugene
    Mar 29, 2022 at 3:50
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    @RobbieGoodwin it's hard to define 'harder', I would like to measure how afraid a rider would be for a given wind.. but it's subjective.. I guess more objective measure is, how big is the accerelation of the body movement due to the side wind
    – eugene
    Mar 29, 2022 at 3:53

3 Answers 3

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Humans are approximately cylindrical/spherical.

This means the square cube law applies to us. Our volume (and therefore mass) grows faster than our surface area. Or put another way: A 100kg human usually doesn’t have twice the surface/frontal area of a 50kg human. The increase is far smaller. At the same time force and power output of the human scale much better with mass and size.

This means that taller, heavier riders are less affected by wind and their aerodynamic drag is lower relative to their size, mass and power output.

Heavier (and therefore stronger) riders should also have an easier time holding the handlebars steady when steering against crosswinds.

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  • this assumes, human grows in 3 dimensional directions.. I guess your argument would be correct in that assumption. Upon seeing your answer, I realized I'm assuming a slightly different scenario where two people with same height differ in weight only. In that scenario, I concluded heavier person is more affected, because twice heavier person would have more than twice surface area. (I assumed fat is lighter than bones and waters)
    – eugene
    Mar 29, 2022 at 3:49
  • @eugene: Someone who’s twice as heavy as another person of the same height won’t have twice the surface area. I’m having a hard time finding numbers, but a quick look at T-Shirt sizes (e.g. here) shows that from S to XXL the area only increases by 40% while 1.8m tall men wearing them could probably be around 65kg and 120kg (I don’t know how heavy one has to be for XXL).
    – Michael
    Mar 29, 2022 at 5:14
  • Assuming cylindrical, surface of the side is defined by 2pirh . Whereas volume is defined by pirr*h. If we assume same density and same height.. twice heavier person would have root-2 larger radius therefore root2 larger surface.. you r correct
    – eugene
    Mar 29, 2022 at 5:19
  • But then, I have to consider that mass density is not the same for 50kg person and 100kg person .. ie how heavy is excessive fat compared to bones and other body substances
    – eugene
    Mar 29, 2022 at 5:25
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    @eugene Here's another detail for you--it depends on how they dress. If everyone is wearing the same type of gear then this doesn't come into play, but if the weather is in that range where some people need to wear more than others then skinny people tend to get colder than bulky people (bulky people have a built in jacket)--so probably most of the skinny people are actually the same volume and surface area as the bulky people at that point. Mar 29, 2022 at 15:17
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There's also bigger as in taller, which definitely affects your response to wind, for several reasons:

  • The wind is stronger further from the ground.
  • Similarly, but not the same, tall people are more likely to stick up above hedges and fences.
  • The same wind acting on a longer lever will have more effect.

Of course we can get low, but there's a limit to how low given the height of our bikes. The extra weight that comes with height does provide a bit of ballast, but the centre of gravity is higher for a higher rider too.

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  • “The same wind acting on a longer lever will have more effect.” But a long lever should also be easier to balance.
    – Michael
    Mar 28, 2022 at 11:26
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    @Michael quite possibly so, and actual balancing is rarely an issue. Because of the interplay between balance and steering, the immediate effect of a sudden gust (or passing a gap in a hedge) will still be to knock you off course
    – Chris H
    Mar 28, 2022 at 11:30
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Yes, the larger the sail the more force moving the ship.

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    Which, in this case, is counterbalanced to some degree by a heavier ship.
    – MaxD
    Mar 28, 2022 at 13:57
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    @MaxD ship analogy does not work with bikes for the righting moment - for ships (sailing in particular) center of mass is below center of buoyancy making it to want go back to vertical with bottom down when center of mass shifted side ways; for bikes center of mass is above the point where it touches the ground and shifting the CM sideways only makes it to move more in the same direction till CM is on the ground :) Mar 28, 2022 at 20:44
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    @AlexeiLevenkov Mass still matters because of inertia (in case of gusts), and you also have to lean less into the wind to stay upright (in case of steady wind). Both of which make it easier for the rider.
    – MaxD
    Mar 28, 2022 at 21:12

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