Cycling with a tailwind

MrCreosote

You'll be breaking rule 24 of the Euro cyclist rules by replying to me, but I'd be interested in getting opinions.

Say you know you're going to have a decent tailwind for a few kms is it better to stay down on the aerobars? Or to sit up and try to catch the wind?

Sort of like reverse aerodynamics?

Lumen

If you can feel the wind on your face, get lower. If you can't, get higher.

No idea about crosswinds.

Jawgap

First, what's a tailwind - I'm not familiar with the concept:)

For crosswinds, I'd say stay low - you won't get any "push" but you'll reduce your cross section making it easier to steer and maintain stability.

iregk

With a tailwind I try to stay high to catch it as much as possible. Head wind get aero.

blorg

Lumen wrote: »

If you can feel the wind on your face, get lower. If you can't, get higher.

No idea about crosswinds.

I think you are almost always better in an aero position, even with a tailwind. It is a rare rare day indeed where it seems faster sitting up. Maybe happens once or twice a year. Part of this is probably due to the fact that a tailwind will basically never be absolutely behind you; I read somewhere a study showing wind was a detrimental factor around significantly more than a 180 degree arc around the cyclist, e.g. even if it is partially behind you but mostly a crosswind it is still a net negative. I'll try to dig that one out. Even with a tailwind pretty much behind you wind tends to change and if you are in a non-aero position any changes or gusts will have a detrimental effect on you.

May also be of interest

Lumen

blorg wrote: »

I think you are almost always better in an aero position, even with a tailwind. It is a rare rare day indeed where it seems faster sitting up. Maybe happens once or twice a year. Part of this is probably due to the fact that a tailwind will basically never be absolutely behind you; I read somewhere a study showing wind was a detrimental factor around significantly more than a 180 degree arc around the cyclist, e.g. even if it is partially behind you but mostly a crosswind it is still a net negative. I'll try to dig that one out. Even with a tailwind pretty much behind you wind tends to change and if you are in a non-aero position any changes or gusts will have a detrimental effect on you.

May also be of interest

Indeed, it doesn't happen very often.

The other factor is that you can generally produce more power sitting up, so as a rule if I feel like I'm cycling in still air I adopt a hands-on-tops climbing position.

Jawgap

I'm sure someone will work out the maths of it - but if you are "up" for a tailwind - let's assume it's directly behind you - and getting a push from it, won't your upright body posture also increase drag?

So is there a "threshold" windspeed below or above which one should stay down?

Raam

blorg wrote: »

I read somewhere a study showing wind was a detrimental factor around significantly more than a 180 degree arc around the cyclist, e.g. even if it is partially behind you but mostly a crosswind it is still a net negative.

Lumen wrote: »

The other factor is that you can generally produce more power sitting up, so as a rule if I feel like I'm cycling in still air I adopt a hands-on-tops climbing position.

Jawgap wrote: »

llet's assume it's directly behind you - and getting a push from it, won't your upright body posture also increase drag?

So is there a "threshold" windspeed below or above which one should stay down?

My god, you chaps really take the fun out of cycling.

Lumen

Raam wrote: »

My god, you chaps really take the fun out of cycling.

I take it you won't be interested in my prototype head tube mounted anemometer then?

Raam

Lumen wrote: »

I take it you won't be interested in my prototype head tube mounted anemometer then?

Hold on, you can buy stuff for the bike to measure the wind? Why didn't you tell me earlier?!

Jawgap

Lumen wrote: »

I take it you won't be interested in my prototype head tube mounted anemometer then?

already got one


Of course - if you go to San Diego

blorg

The iBike power meter measures wind speed, it uses this and gradient to figure out the power. Not meant to be a very good power meter (among other issues it will only work while you maintain the same position) but it certainly does the wind.

blorg

Jawgap wrote: »

I'm sure someone will work out the maths of it - but if you are "up" for a tailwind - let's assume it's directly behind you - and getting a push from it, won't your upright body posture also increase drag?

So is there a "threshold" windspeed below or above which one should stay down?

It would have to be pretty much constant and directly behind you. (This never happens.) It would also have to be faster than you are travelling. If you are cycling at 35km/h and have a 20km/h tailwind directly behind you (which never happens) this means you are pushing into an effective 15km/h of air resistance in front of you and would be better off in an aero position.

Lumen

blorg wrote: »

It would have to be pretty much constant and directly behind you. (This never happens.) It would also have to be faster than you are travelling. If you are cycling at 35km/h and have a 20km/h tailwind directly behind you (which never happens) this means you are pushing into an effective 15km/h of air resistance in front of you and would be better off in an aero position.

From an efficiency perspective, yes. However, the difference between aerobar and hoods positions at 15kph windspeed is something like 7W, which you would likely more than make up for with increased power generation in the more upright position.

nomdeboardie

Jawgap wrote: »

I'm sure someone will work out the maths of it - but if you are "up" for a tailwind - let's assume it's directly behind you - and getting a push from it, won't your upright body posture also increase drag?

So is there a "threshold" windspeed below or above which one should stay down?

Re aerodynamics, maybe stay up if travelling slower than the tailwind, then down if faster? (Not considering pedalling efficiency differences as mentioned by other posters)

-K2-

Lumen wrote: »

I take it you won't be interested in my prototype head tube mounted anemometer then?

Only works in the aero position.

peterako

blorg wrote: »

May also be of interest

My own 'empirical' results tend to disagree.

On the 'rare occassions' that there is a wind my round trips are notably faster than the same journey on a still day...

Possibly because of my enourmous frontal area?

At least with the wind I get a portion of the ride where I'm being blown along and therefore have a slight rest

Looking through my older logs confirms the diferences...

As to the original question (and further confirming my non-Euroness)....

I try and keep aero all the time, but ultimately comfort wins out and for tail winds, as long as I feel it's not unduly slowing me down I choose a comfortable position

blorg

Lumen wrote: »

From an efficiency perspective, yes. However, the difference between aerobar and hoods positions at 15kph windspeed is something like 7W, which you would likely more than make up for with increased power generation in the more upright position.

Fair enough but you would need to be able to measure both wind speed and direction and have the wind directly behind you and constant- which never happens!

My own subjective experience is that sitting up on the flat almost never makes it better, even with a perceived tailwind. Maybe once a year when there is an absolute gale blowing directly behind me.

blorg

peterako wrote: »

On the 'rare occassions' that there is a wind my round trips are notably faster than the same journey on a still day...

I would definitely find the opposite, no question I am slower with a wind on an out and back compared with a still day. AFAIK this is regularly borne out in out and back time trials, a still day results in better times.

Lumen

blorg wrote: »

My own subjective experience is that sitting up on the flat almost never makes it better, even with a perceived tailwind. Maybe once a year when there is an absolute gale blowing directly behind me.

Yes, but this is just because you've dropped the tailwind and it's gone home to mope about how inadequate it is.

Beasty

blorg wrote: »

I would definitely find the opposite, no question I am slower with a wind on an out and back compared with a still day. AFAIK this is regularly borne out in out and back time trials, a still day results in better times.

+1
I have 2 years of spreadsheets backing this one up:)

Lumen

Beasty wrote: »

+1
I have 2 years of spreadsheets backing this one up:)

And the calculator agrees.

20km journey, comparing still conditions to parallel wind, constant power output.

200W @ still = 31.76kph, 37.78 minutes.
200W @ 10kph = 25.89kph, 46.35 minutes.
200W @ -10kph = 38.28kph, 31.35 minutes.

Return trip with no wind = 75.56 minutes.
Return trip with 10kph parallel wind = 77.7 minutes.

Interestingly, the "average" windy speed (taken crudely/wrongly as the mean of the two average speeds) comes out higher with wind, but the overall trip takes longer.

This is because the tailwind helps you for less time than the headwind hurts you.

blorg

Lumen wrote: »

200W @ still = 31.76kph, 37.78 minutes.
200W @ 10kph = 25.89kph, 46.35 minutes.
200W @ -10kph = 38.28kph, 31.35 minutes.

Slightly off-topic but those are really large differences for only 10kph steps in wind speed, I am surprised.

Lumen

blorg wrote: »

Slightly off-topic but those are really large differences for only 10kph steps in wind speed, I am surprised.

10kph tailwind adds 6.5kph to your 32kph speed; it's not entirely surprising, given that aero drag is such a large proportion of total resistance.

Look at it another way - at 40kph with a 10kph tailwind you have the same windspeed as at 30kph, only a little more rolling resistance to overcome.

blorg

Lumen wrote: »

10kph tailwind adds 6.5kph to your 32kph speed; it's not entirely surprising, given that aero drag is such a large proportion of total resistance.

Look at it another way - at 40kph with a 10kph tailwind you have the same windspeed as at 30kph, only a little more rolling resistance to overcome.

I understand the theory, I just wouldn't have thought I see those differences comparing forecasted wind speeds and my actual cycling speeds. 10kph is a very low wind. The variance I see is less than that. Of course it won't be exactly aligned and I probably try harder into the wind, I would see that if I bought a power meter I guess.

Lumen

blorg wrote: »

I understand the theory, I just wouldn't have thought I see those differences comparing forecasted wind speeds and my actual cycling speeds. 10kph is a very low wind.

From here.

"The international standard height for wind measuring instruments is 10 meters (32.8 feet) above ground level"

peterako

blorg wrote: »

I would definitely find the opposite, no question I am slower with a wind on an out and back compared with a still day. AFAIK this is regularly borne out in out and back time trials, a still day results in better times.

I forgot to mention.....I'm SEVERAL levels slower than a very slow Weekend Warrior

IM0

this thread reminds me of the"if a tree falls in a forest does it make a sound" arguement

Slideshowbob

How do you know it's a tailwind?

Captain Havoc

Slideshowbob wrote: »

How do you know it's a tailwind?

I find the wind usually comes from my tail

blorg

Slideshowbob wrote: »

How do you know it's a tailwind?

You feel great, and then you turn around.

Slideshowbob

blorg wrote: »

You feel great, and then you turn around.

that could be a decent!

DirkVoodoo

A headwind is great for working out the inefficient points in your posture. Elbows bent people!

On the rare days I get a tailwind it doesn't do me too many favours as 44-16 tends to spin out quite easily. Give it to me hard and in the face!

IM0

DirkVoodoo wrote: »

Give it to me hard and in the face!

need I add a witty remark here or is highlighting this enough

DirkVoodoo

me@ucd wrote: »

need I add a witty remark here or is highlighting this enough

Don't worry it was entirely intentional! We're talking about the wind right?

IM0

DirkVoodoo wrote: »

Don't worry it was entirely intentional! We're talking about the wind right?

Dirkvoodoo wrote:

elbows bent people

Dirkvoodoo wrote:

give it to me hard and in the face!

Are we?