Aero position significance depending on speed/wind

I have heard it said that an aero position only matters if you are going over 17 mph, so basically you don’t need to assume a bent elbow position when climbing. Is this true?
And how does wind effect this? It would seem like the effects of a strong wind would change this 17 mph limit. On a recent ride, there was another rider who pulled for a lot more than I did, and I thought he was stronger, but really his power for the ride was substantially lower than mine. It was very windy and he used an aero position most of the time, while I did only some of the time, so maybe that is the difference?

Some might dispute the specific 17mph value (others state lower speeds), but that divergence aside… the real issue here is “relative wind speed”. This is the total of rider motion forward (ground speed) and any component of wind added to that.

Super simple example:

  • Rider at 10mph forward ground speed + 10mph pure tailwind (behind the rider) = 0mph relative wind speed on the rider. In a case like that, where rider speed is equal to tailwind, there is no need to “get aero”.

More to your climbing example:

  • Rider at 10mph forward ground speed up a hill + 10mph direct headwind (into the front of the rider) = 20mph relative wind speed. In this case, it could very well make sense to adopt an aero position.

So, “it depends” and the end result is the final relative wind speed that the rider experiences. If you end up with a strong enough tail wind, you are actually better off to sit up and embrace that wind for a “push”. :stuck_out_tongue:


This all makes total sense to me, and seems pretty simple to intuitively implement - thanks!

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Intuitively I thought of that the other day on my training loop. Had a head wind in one direction and tail wind in the other. I remember thinking should I adopt an aero position in one way or the other. Ended up kinda doing both. Until my lower back told me to slack the aero position lol.
All that to say, all the talk about aero gains being exponentially more important at high speed. People should rather talk about relative wind difference then.

On a out and back TT with a head wind one way tail wind the other. Would you rather push harder with or against the wind? Or would you just pace it evenly regardless of terrain/wind conditions?

Push harder into the wind - TTs aren’t about going fast, they are about not going slow. (Same applies for gradients).

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  • This is the type of question that Best Bike Split was designed to address. It takes into account your equipment, CdA, route elevation and orientation, along with historic (and predicted?) wind conditions to craft a pacing plan for events.

  • It digs far into the comparisons of where it makes sense to spend more watts than others. In short, it’s quite complicated once you look at the full range of factors. There are some general concepts than can help, but they are far from concrete or absolute.

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well not quite in example 1, you still have to overcome air resistance, (assume the road has a zero gradient so flat) whether it is 0 or 10 mph, there is air and it is dense, thus no matter the air speed aero will result in a faster net speed vs sitting up in a non aero position. So assuming you are moving forward, then aero helps and you get more speed per watts input. When air speed is >0 then the benefits become more pronounced due to the equation wherein speed is a squared value, so more net air speed the greater the aero benefit because as you go faster (increased net air speed) the input power goes up in a non linear fashion.

Example 2 further complicates the issue by including the gravity component which I assume example 1 did not, ie on a level road.

Lots to unpack in these examples, and probably even these are super over simplifications.

Of course, reality is more messy. Hence the reason I lead to a “super simple example” that aimed to get at a root issue. I know it’s not perfect, all inclusive or accurate, but the basic point still stands in both cases.

Even at slow ground speeds, it may make sense to “get aero” if you have enough headwind. And the inverse may be true if you have enough tailwind.

All this is academic to a point, because it’s far from easy to evaluate this in the moment when actually riding. All we can do is guestimate based on our known ground speed (if we have a speedo), and the senses we have about the wind around us (feeling of wind on arms, ears and such as well as possible “wind socks” from flags, grass, trees and such). It’s all probably quite fuzzy when we also recognize the instances of pure head/tail wind are more rare, while mixed angle is likely more common.

So, it’s all fuzzy math in the real world. All I wanted to do was touch on basic ideas without all that muddy water.

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The simple example, while a simplification, did get across the practical point that relative wind speed is worth considering while riding, so thanks for that!

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if you are curious you can use this calculator to see how things change:

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