# 'Make a sail' or 'go aero' uphill with a stonking tailwind?



## ColinJ (24 May 2016)

I normally go UP the long local Cragg Vale climb and there is usually a SW cross/headwind to contend with. Today I forgot to check the forecast and set off to do my loop in the opposite direction for a change. It was soon obvious that there was a reversal to the usual wind direction. When I got to the summit at Blackstone Edge, I turned left and began my descent. It is normally easy to hit 50+ kph even on the shallow downhill gradient before it steepens further on. Today, the wind was so strong against me that I was only doing 25 kph on the first part of the descent.

I saw a rider coming up the hill towards me at a brisk pace. He had tribars on his bike and was using them.

It struck me that he probably wasn't going much faster up the hill than his tailwind ...

Then I wondered ... If his speed relative to the air was that low, would he have been better off sitting up to catch more of the wind?

It is all very well theorising. I suppose the real answer would be to try both ways using a power meter to keep the effort the same but I don't have tribars OR a power meter.

Somebody satisfy my curiosity - in that scenario and for the same level of effort, 'make a sail' or 'go aero' to go faster?


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## Rohloff_Brompton_Rider (24 May 2016)

My big masculine muscular back caught the wind up Manchester Rd today and I averaged 9mph, which meant I was 5 minutes too early for tea.


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## rualexander (24 May 2016)

The pushing effect of a tailwind is fairly negligible, in normal everyday wind strengths, imagine standing up on a windy day and jumping off the ground, do you get blown any distance? 
The main assistance from a tailwind is in the reduction or absence of any air resistance to your forward movement, depending on the wind strength.
Therefore, going uphill with a tailwind, I would say the person you saw would have seen little difference in either position.


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## 2IT (25 May 2016)

While the sail effect may not be great, it's an excellent time to change body position. Besides using the muscles at a different angle it opens up the breathing, gives the neck a break etc... Whenever I can, I do. 


ColinJ said:


> I normally go UP the long local Cragg Vale climb and there is usually a SW cross/headwind to contend with. Today I forgot to check the forecast and set off to do my loop in the opposite direction for a change. It was soon obvious that there was a reversal to the usual wind direction. When I got to the summit at Blackstone Edge, I turned left and began my descent. It is normally easy to hit 50+ kph even on the shallow downhill gradient before it steepens further on. Today, the wind was so strong against me that I was only doing 25 kph on the first part of the descent.
> 
> I saw a rider coming up the hill towards me at a brisk pace. He had tribars on his bike and was using them.
> 
> ...


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## slowmotion (25 May 2016)

My guess is that the "sailors" could be on to a good thing if the sail is big enough. With a big sail, you are capturing a larger force to propel you along the road. With a tail wind, you will never be forced along faster than the windspeed itself when going in a straight line with the wind directly behind you. However, if you hold out your billowing hi-viz jacket and tack down the road, you could reach totally awesome speeds. I hope this helps.....


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## Rohloff_Brompton_Rider (25 May 2016)

Ok, if a tail wind is negligible, explain to me why the same wind strength but as a head wind, is why on many occasions, I have had to pedal down the 6% mile long section on the way home?


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## machew (25 May 2016)

View: https://www.youtube.com/watch?v=GOnM1lXENj4


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## raleighnut (25 May 2016)

machew said:


> View: https://www.youtube.com/watch?v=GOnM1lXENj4


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## Yellow Saddle (25 May 2016)

just_fixed said:


> Ok, if a tail wind is negligible, explain to me why the same wind strength but as a head wind, is why on many occasions, I have had to pedal down the 6% mile long section on the way home?


Because the wind assistance was not enough to overcome rolling resistance?


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## Yellow Saddle (25 May 2016)

Sail away but don't expect huge benefits. Your body is smaller and forms a poorer sail than you think.


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## 2IT (25 May 2016)

My body feels like an umbrella or parachute into a headwind and a sail in a side wind.


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## MiK1138 (25 May 2016)

What is this tailwind you speak of


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## 400bhp (25 May 2016)

rualexander said:


> The pushing effect of a tailwind is fairly negligible, in normal everyday wind strengths, imagine standing up on a windy day and jumping off the ground, do you get blown any distance?
> The main assistance from a tailwind is in the reduction or absence of any air resistance to your forward movement, depending on the wind strength.
> Therefore, going uphill with a tailwind, I would say the person you saw would have seen little difference in either position.



Is this because essentially you create a (for want of a better phrase) "dead zone" in front of you as your back is shielding the airflow? When the wind is directly behind Ithere appears to be little or no noise.


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## rualexander (25 May 2016)

Its not so much that you create a 'dead zone' although you do to some extent if the tailwind speed is greater than your road speed, its more that the air is flowing the same way as you are going so you don't have to push through it.
The reason it is quieter with a tailwind is because you don't have air rushing over the front of your ears.


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## ColinJ (26 May 2016)

I enjoy the quietness of riding with a tailwind even more than the help it gives me. One minute I am battling a deafening crosswind then I turn a corner and the riding becomes easy and silent - bliss!

Yes, but depressingly rare ... The valley system round here seems to funnel the winds in a strange way. It is often possible to do a circular ride and get cross/headwinds 75+% of the time!


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## mjr (26 May 2016)

ColinJ said:


> Yes, but depressingly rare ... The valley system round here seems to funnel the winds in a strange way. It is often possible to do a circular ride and get cross/headwinds 75+% of the time!


Oh everywhere has quirks like that. If you live on the coast or near a major estuary, tidal winds can give you headwinds 75+% of the time... but I did one 100 mile ride last year where we had tailwind or cross-tail wind for 81 miles, which I think was partly due to that effect. The 19 miles into a battering headwind still felt like 1900, though!

Back to the question: I'd sit up every time - not quite "make a sail" if it's uphill, but I've freewheeled over 20mph on the flat thanks to a tailwind before. Mind you, we only managed 6mph into that wind, so the average still stank.


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## Oldfentiger (26 May 2016)

Yer all overthinking it!
Have you got a NET tailwind or headwind.
Examples......
If you're pedalling at 10mph with a 15mph tailwind then you have a net tailwind of 5mph, so sit up and reap a miniscule benefit.
If you're pedalling at 10mph with a 5mph tailwind then you have a net headwind of 5mph, so get down and reduce your frontal area (unless you can raise a 5mph fart).


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## derrick (26 May 2016)

I would say sit up. We have a couple of strava segments we do regularly, With a good tail wind you can save a bit of time, Depending how strong that wind is.


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## 2IT (26 May 2016)

Isn't it ironic and unfortunate that our backside is more aero than the front side? 

So while we would like to catch a lot of tailwind, we usually just pass it.


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## ufkacbln (27 May 2016)

Mike Burrows explained it something like this very simplified version:

Stand up and put your arms out - any wind direction forward of your arms will have a head wind component, and affect your forward motion


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