Does wind help or hinder your average speed?

CleeRider

I'm a beginner so don't have a lot of experience to go on, so please chip in...
I always aim to beat my best average speed so should I be avoiding days with a 15mph wind and looking for still days?

For simplicity sake imagine I go out down a dead straight road for 2 miles into a head wind and then return home.
If I normally average 15.5mph and do 12.5mph into a 15mph head wind; and 22mph with the equivalent tail wind.
Then simple maths would show that it would boost my average speed, but if i did 20 miles under those conditions with all of the extra exerted energy associated with the head wind over the first 10 miles, would this still hold true?

Also, what about if the tail wind came on the outward bound leg of the journey and coming home was tough?

I do realise that you would rarely ride on a straight road in this way for 20 miles, and that 15mph isn't exactly a gale but it would make interesting reading for me to hear how wind affects everybody.

turnerjohn

get out and ride....if your waiting for the perfect day your be missing most of the year !
Use a heart rate monitor (power if you can afford it) and ride / train hard and your speed will naturally improve

dodgy

Short answer, any ride that starts and ends at the same point on the map, will be adversely affected by wind. In other words, your overall average will be higher on still days.

It's the same on very hilly rides, you'd think that the ascents would be cancelled out by the descents, but they're not, because you spend much longer in time on the ascent and any increase in speed on the descent is only for a short time because you're going faster.

Imagine a rider that can normally ride at 20mph in ideal conditions, he decides to ride to the northern tip of Lanzarote from the southern tip, a distance of 50 miles. But there is a very strong headwind on the way north and this has brought his speed down to a realistic (I've done it!) 12.5mph, so it takes him 4 hours to get there. Now he only has an hour to make the return journey south, and to regain his usual average speed of 20mph would require him to return south at 50mph - it's not going to happen.

Hope this helps.

Oh and like turnerjohn says, it's not worth obsessing over, just ride.

elderone

my averages are around 15mph where i ride as its ups and downs..on a level bit i can cruise at 22-24 mph but if i only rode flat road id have 20+ average,but i dont so all things have to be considered.maybe measure yourself over a month in all conditions and that will give you a better over all average.

cookeeemonster

I'm pretty sure that to get any benefit from a tailwind it'll have to be going faster than you - i.e. if you're traveling at 15mph and the tailwind is at 16mph+ then you'll get a benefit...else it wont make any difference except that it's not a headwind - which will slow you down

basically just see headwinds as a training aid

Mikey23

hills and wind... makes us strong

danowat

Winds are a good bit of resistance training, but you can't (at least IME) make up on the tailwind, what you lose on the headwind

dodgy

CookeeeMonster wrote:

I'm pretty sure that to get any benefit from a tailwind it'll have to be going faster than you - i.e. if you're traveling at 15mph and the tailwind is at 16mph+ then you'll get a benefit...else it wont make any difference except that it's not a headwind - which will slow you down

basically just see headwinds as a training aid

Nope Even a 1mph tailwind is helping you, even if you're travelling at 20mph.

turnerjohn

dodgy wrote:

CookeeeMonster wrote:

I'm pretty sure that to get any benefit from a tailwind it'll have to be going faster than you - i.e. if you're traveling at 15mph and the tailwind is at 16mph+ then you'll get a benefit...else it wont make any difference except that it's not a headwind - which will slow you down

basically just see headwinds as a training aid

Nope Even a 1mph tailwind is helping you, even if you're travelling at 20mph.

^ totally....even more if your a sail

rolf_f

CookeeeMonster wrote:

I'm pretty sure that to get any benefit from a tailwind it'll have to be going faster than you - i.e. if you're traveling at 15mph and the tailwind is at 16mph+ then you'll get a benefit...else it wont make any difference except that it's not a headwind - which will slow you down

You are confusing the helping effect with the feeling of the wind behind you effect.

As already said, even a 1mph tailwind is a tailwind. Instead of riding into air at eg 20mph, you are riding into air at 19mph. That's a benefit. But you are still riding into air at 19mph.

Of course, the trouble is that with eg a 20mph tailwind, you'll probably ride harder and end up doing 30mph and feel like you are riding into a 10mph headwind. Usually the best you get in terms of feel is the lovely still air feeling when the tailwind matches your speed. The only time I usually feel a tailwind actually pushing me is if I am on my mountain bike and climbing.

Slack

Rolf F wrote:

Of course, the trouble is that with eg a 20mph tailwind, you'll probably ride harder and end up doing 30mph and feel like you are riding into a 10mph headwind. Usually the best you get in terms of feel is the lovely still air feeling when the tailwind matches your speed. The only time I usually feel a tailwind actually pushing me is if I am on my mountain bike and climbing.

This is so true. Those days when you're riding and thinking 'hm I should have a tail wind, but feeling some air resistance like a headwind, wind must have changed direction', only to turn the other way and feel the real headwind.

marcusjb

What is this tailwind that people are talking about? Not something I ever seem to experience!

b45her

everyone knows that wind always blows down hill too, at least it does in wales anyway.

nickyboy zz

dodgy wrote:

Short answer, any ride that starts and ends at the same point on the map, will be adversely affected by wind. In other words, your overall average will be higher on still days.

It's the same on very hilly rides, you'd think that the ascents would be cancelled out by the descents, but they're not, because you spend much longer in time on the ascent and any increase in speed on the descent is only for a short time because you're going faster.

Imagine a rider that can normally ride at 20mph in ideal conditions, he decides to ride to the northern tip of Lanzarote from the southern tip, a distance of 50 miles. But there is a very strong headwind on the way north and this has brought his speed down to a realistic (I've done it!) 12.5mph, so it takes him 4 hours to get there. Now he only has an hour to make the return journey south, and to regain his usual average speed of 20mph would require him to return south at 50mph - it's not going to happen.

Hope this helps.

Oh and like turnerjohn says, it's not worth obsessing over, just ride.

Not sure about this one. If you imagine a perfect U shaped valley, ride down one side and use just momentum to go up the other side you will fail to get to the top. The reason is that wind resistance is proportionate to the square of your velocity. Therefore the slowing effect when you go down the hill fast is much greater than the wind resistance "benefit" you get by travelling slowly back up the hill.

Head/Tail winds on a flat ride are completely different. The advantage of riding with the tail wind should be equal to the disadvantage of riding into the head wind. However, this rarely seems to work out. Presumably this is something to do with rolling resistances (are they proportionate to speed?) and/or we just don't try as hard as we should in the tailwind section

dodgy

Nope, I read a very convincing article with lots of physics and maths and stuff on the subject It boils down to you spend longer on the ups than on the downs, so any speed increases on the downs don't last long enough to increase your average speed enough to make up for the slowness on the climbs.

Honest.

Pross

elderone wrote:

my averages are around 15mph where i ride as its ups and downs..on a level bit i can cruise at 22-24 mph but if i only rode flat road id have 20+ average,but i dont so all things have to be considered.maybe measure yourself over a month in all conditions and that will give you a better over all average.

Really?

SBezza

Pross wrote:

elderone wrote:

my averages are around 15mph where i ride as its ups and downs..on a level bit i can cruise at 22-24 mph but if i only rode flat road id have 20+ average,but i dont so all things have to be considered.maybe measure yourself over a month in all conditions and that will give you a better over all average.

Really?

I am sure he means with a tailwind

lotus49

dodgy wrote:

Nope, I read a very convincing article with lots of physics and maths and stuff on the subject It boils down to you spend longer on the ups than on the downs, so any speed increases on the downs don't last long enough to increase your average speed enough to make up for the slowness on the climbs.

Honest.

Was it this article by any chance? http://sheldonbrown.com/brandt/wind.html.

It does support your conclusion.

There was also an item on Bang Goes the Theory (available on an iPlayer near you when it's on anyway) that posed exactly the same question and Dr Yann came to the same conclusion.

dodgy

lotus49 wrote:

dodgy wrote:

Nope, I read a very convincing article with lots of physics and maths and stuff on the subject It boils down to you spend longer on the ups than on the downs, so any speed increases on the downs don't last long enough to increase your average speed enough to make up for the slowness on the climbs.

Honest.

Was it this article by any chance? http://sheldonbrown.com/brandt/wind.html.

It does support your conclusion.

There was also an item on Bang Goes the Theory (available on an iPlayer near you when it's on anyway) that posed exactly the same question and Dr Yann came to the same conclusion.

That looks familiar, there's also one with some aviation derived formulas that show that pilots need to take more fuel when flying in windy conditions, even if they're returning to the same location.

dodgy

Also good discussion here on it, someone has brought up the pilot/fuel/wind thing up there, too http://boards.straightdope.com/sdmb/sho ... p?t=654711

'aerodave' pretty much nails it with this comment:

"Averaging different speeds can lead to some non-intuitive answers. If you ride 10 mph for a mile, and then 30 mph for a mile, you can't just average 10 and 30 to get 20 mph. That's because the unit "mph" also includes time. And it's the time you spend going each speed that has to be averaged. So the first mile took 6 minutes, and the second took 2 minutes. The resulting average is 2 miles in 8 minutes, or 15 mph. Notice the average speed over that ride is far closer to the slower speed, because you spent triple the time going that slow.

For that reason, hills always reduce your average speed. Even cancelling all the elevation change by doing an out-and-back doesn't buy back the time you have to put in climbing. You can't spend enough time on the descents to really boost your average speed."

owenlars

dodgy wrote:

Imagine a rider that can normally ride at 20mph in ideal conditions, he decides to ride to the northern tip of Lanzarote from the southern tip, a distance of 50 miles. But there is a very strong headwind on the way north and this has brought his speed down to a realistic (I've done it!) 12.5mph, so it takes him 4 hours to get there. Now he only has an hour to make the return journey south, and to regain his usual average speed of 20mph would require him to return south at 50mph - it's not going to happen.

This says it all very eloquently. It is an immutable law of nature, on a circular course with a steady wind you will always go slower overall than if there was no wind. Applies to runners, light aircraft, bikes, in fact anything where the wind speed is a significant proportion of the vehicle's speed.

Ron Stuart

Dodgy is correct if you have the same conditions around a fixed circuit then 0 wind speed should be quickest but if you set of for example on an out and back towards a wind that builds on the return and was light on the out then your average speed will benefit. Also terrain can influence if you do a circuit that has a lot of cover from the wind (twists and turns with high hedges) when you are generally aiming towards the wind but then on the return with the wind the road is general straight downwind, wide and exposed then this could also benefit your average speed.
So answer unfortunately is..... it depends :!: but Dodgy's theory is still sound though.

logie48

Well i'd like to think if you ate a can of baked beans an hour before your ride, it would certainly help with your average speed.

nickyboy zz

Right, finally got it sussed, it just needed another coffee for the penny to drop.

Imagine riding at 10mph with a 6 mph tailwind, then turning round and riding the same with a 6 mph headwind. In the tailwind section you will have an effective headwind of 4mph, on the return leg it will be 16mph

The wind resistance effect is proportionate to the square of the EFFECTIVE speed so on the outbound it is 4x4 = 16. On the inbound it is 16x16 = 256 so the total is 16 + 256 = 272

Now if there is no wind the outboud and return legs both have an effective speed of 10mph so the wind resistance effect is 10x10 = 100 per leg so 200 in total.

So in this example, you suffer 36% more wind resistance than in still air

Rode back over the Snake Pass yesterday into a 30mph headwind so I know only too well the effects

jecooper

unfortunately you're still completely ignoring the effect of time in your logic above. the answer is that you'll be experiencing exactly the same assistance from the wind (in terms of force) going out as you will be negatively effected on the way back. The difference in performance comes from the fact you'll spend more time being hindered rather than assisted so therefore the overall contribution is negative. the same logic applies to the perfect bell shaped hill.

fortunately the whole effect can be negated by swapping the bacon buttie for some warm porridge so go have fun!

Ron Stuart

jecooper wrote:

unfortunately you're still completely ignoring the effect of time in your logic above. the answer is that you'll be experiencing exactly the same assistance from the wind (in terms of force) going out as you will be negatively effected on the way back. The difference in performance comes from the fact you'll spend more time being hindered rather than assisted so therefore the overall contribution is negative. the same logic applies to the perfect bell shaped hill.

fortunately the whole effect can be negated by swapping the bacon buttie for some warm porridge so go have fun!

As a helm that has sailed in many world and national championships along with riding a bike for the last 55 years. I can safely say that during a period of say 3 hours the wind does not blow at a constant speed or direction. Further more I have watched with keen interest how quite often the riders in Pro Tour TT's experience wind conditions that vary a lot during their rides. There is quite often an even greater disparity throughout the time it takes for the whole peloton to complete a TT stage.
Your hypothesis is quite correct in certain wind conditions but not all.