I think I missed a lot of opportunities to go faster when cruising and not taking advantage of tailwind. I find that if I put short effort in acceleration, the tailwind will take care most of the speed maintaining work.

For big tailwind I can usually see leaves rolling on along my general direction. Lately, I think if wind noise is more quite, I might be in tailwind?

So how can you tell if you've got tailwind or wind direction in general? (without flag anywhere nearby)

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Only if it is for Strava PR ( or whatever record you set) you can say you missed, but you cannot actually "miss" it unless you stop... There is maybe another question you are asking, is there an optimal speed at which you take more advantage of a tailwind? – gaurwraith 7 hours ago
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Generally speaking, if you're marveling at how well you're riding, you have a tailwind. Otherwise, you can look at vegetation, but it can often be deceptive. – Daniel R Hicks 7 hours ago
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@DanielRHicks are you sure? I am not convinced that the 70+ kph tailwind I experienced had anything with me maintaining at 60+ kph average over an 80 km ride many moons ago. – Rider_X 4 hours ago
    
If it's summer and you suddenly get unusually hot while riding, then you probably have a tailwind ;) – rclocher3 3 hours ago
    
@Rider_X You still had to be blasting out the power to overcome the rolling resistance! – andy256 1 hour ago
up vote 3 down vote accepted

The most accurate way to do it would be with a pitot tube to measure wind velocity and then to contrast that against speed-over-ground from your GPS or wheel speed sensors.

Before one laughs about the science-fiction nature of this, there's a product that does so: The PowerPod (link is to DC RainMaker's review of it)

PowerPod

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An air-speed meter vs a ground speed meter. Sounds like something from an aeronautical standpoint. – Criggie 7 hours ago
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Despite all the advances in aviation tech, a little tube stuck in the wind stream is still how they measure wind speed. – RoboKaren 6 hours ago
    
I never said it was a bad idea ! – Criggie 5 hours ago
    
This is perfect! I've been ignoring power meters because of their prices, but this one is like at least $200 cheaper than the next one. – imel96 1 hour ago

We like tailwinds as the effort to ride at a given speed is lowered. In the same token we like slight downward slopes.

If you base your riding on effort, rather than a fixed speed, you will automatically utilise a slight tailwind. If you however ride at a fixed speed, you simply had an effortless ride. In other words, you missed nothing.

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By missed opportunity, I mean like when someone passes by, if I jump behind them, I can draft. Without that jump, sure the effort will be less, but difference is very little that I almost always unaware of. – imel96 2 hours ago

You can check wind direction from bending of vegetation, it stays bent to the wind for longer periods than it springs backwards in eddies, attach a white cotton/wool thread to the handlebars and check it's movement every time the bike slows, feel the wind in left ear, right ear, forwards and back, and check a weather graph with wind direction and speed expected for every hour of the day, and go out when it's max tailwind and come back when it's calmed on the return.

mostly the wind is as likely to be against you as with you, although checking the daily forecast can mean taking advantage of massive tailwinds to get some place very fast and then coming back in relative calm. If you travel through an entire country you can get a map of the prevailing winds for every season and for every region.

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The other rule is that you only get a tailwind when you are climbing a hill on a warm day, and then the wind speed will exactly match your speed. – Daniel R Hicks 7 hours ago
    
Agreed. You only get a tailwind on hot muggy days -- and that tailwind will match your ground speed so precisely to ensure zero airflow over your body. – RoboKaren 4 hours ago

The simplest way is simply stop in an open space and feel where the wind is coming from, using your face. Downside is that any trees or buildings will make the wind veer, and traffic makes its own wind. Plus you have to stop (anathema!)

Flags work really well, because they're often up high and in the real airstream.

You can also check the local weather report for your area. For me that's http://www.metservice.com/towns-cities/christchurch/christchurch but you should have something similar for your location.

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But, but, that requires me to stop!!! What if I'm in the middle of a Strava segment?! I'd miss my PB! – andy256 3 hours ago

@Daniel has made several comments that capture what experienced cyclists have learned.

  • You think something like I'm going well, or killing it, or even (as happened today) this looks like it's uphill, while blasting along.

  • When you stop you discover the awful truth. It's a headwind home.

The reality is that we nearly always have a headwind, especially as Daniel says, when climbing a hill, because we're cyclists. And we usually have a headwind going there, and coming back. That one in a hundred tailwind case is not the first thing we think of.

Yes, vegetation can tell us. But in many cases in a built up environment we can't see any vegetation. But it wouldn't be the first time I've seen the vegetation looking like I have a tailwind when I actually have a headwind. Because I'm a cyclist.

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