headwind

dmch2

I cycled just over 20 miles today all into a headwind that the weather forecast (weather.co.uk) said was about 10-12 mph.

How much different is this likely to have made?

I've only done 3 rides on the bike so I don't yet know what sort of speed I do on it (2nd ride was dark and had a big cross wind so I got scared and braked on the descents, first ride I was scared of the SPD-SLs!).

For the record I managed 16 mph with 1200ft of climbing (that's from eye-balling the altitude plot and only counting 100ft or bigger bumps).

Zendog1

Air resistance is a slightly complicated topic but the fundemental is that the power needed to overcome it goes up with the square of the net air speed (other things like areo profile being equal).

Say you normally ride at 16mph in still air then to maintain the same speed against a 16mph headwind (32mph net - 2 * normal) you need to be putting out 4 times the power.

So yes even quite mild headwinds make a lot of difference - as we all know only to wel l.

To get an exact answer to your question would need need a wind tunnel session and quite a lot of calculations like the pro's do.

Wooliferkins

You seem to have a bike computer? Get a heart rate monitor then you can compare what you put in to what you get out. It will give you an idea of the effort you put in to get the same speed on the same route in differing conditions. At the moment you only have two points speed and time but you dont have the effort measurement.

Hals1967

The winds lately have been really hard work. Even the tailwind seems to decide to shift and come in from the side.

Headwind into a climb now that's the real legbreaker. Can't get down on the drops to climb (at least I can't) so you try and get as low as you can whilst still keeping the cadence up and trying to get as much air in your lungs as you can.

I'm sure it's doing some good

dmch2

I'm aware of the physics of wind resistance (my degree was in Physics) but equally aware that I'm lacking in enough data to calculate it. For example I'm pretty sure that I wasn't putting out anything like enough extra power to deal with the simple calculation you've demonstrated. but equally I know I was having to work harder!

For example it's going to be complicated by the upside of the hills often in the lee of the wind etc.

You're right that a heart rate monitor will let me measure the work I'm doing. but I'll get divorced if I buy any more bike kit after just buying the bike itself!

I just wondered if there was an easy rule of thumb to help massage my ego a bit... (Although I was a fair bit faster than when I last did the route on my hybrid on a calm day so I'm feeling pretty good anyway!)

Could have been worse though, I had a 20+mph wind the other day - fortunately it blew me up the main climb

danowat

After 9 months of commuting, all my data shows that with a tail wind my best time is 54mins, and with a headwind, the worst is 1:06.

So wind can make anything up to a 12min difference on a 17 mile route.

Other than that, I rarely worry about the difference it makes, because 9 times out of 10 on a training run my route is circular, so anything I lose on the upwind leg, I pick up on the downwind leg.

rolf_f

danowat wrote:

Other than that, I rarely worry about the difference it makes, because 9 times out of 10 on a training run my route is circular, so anything I lose on the upwind leg, I pick up on the downwind leg.

If only it worked like that! A tailwind has to be very strong to really make much of a difference and a tailwind that strong will really punish you on the return leg. Besides, winds tend to form cyclones centred on the middle of your training run and running in the opposite direction to the way you are riding

10-12 mph isn't much. Most days for much of the year there have been westerlies of that magnitude up in Yorkshire. Those are fine - it is the equally common gusts of 20-40mph plus that tend to wear me down.

dmch2

My route was a straight WNW route today into a W wind. The commuting stats suggest it's less than a minute a mile difference.

Let's be generous to ourselves and that a 20mph headwind gives a minute a mile difference.

Then the 10 mph wind today might be (cubed law and all that) an eigth of that ie 7 seconds a mile.

Which is only 2 minutes 20 over the 20 miles, about 2%, approximately naff all!

20mph headwind is more meaningful at 15% or so, that could be 3 mph. For a fast rider in our slightly generous world.

Other thoughts...

The wind always swings round to meet you because you're quicker than the wind and the vectors add up like that. Similarly a tail wing never helps much unless it bang on dead behind you.

It's a cube law for power as power is force x speed. And drag (the force you're trying to overcome) squares with speed. So power is speed cubed.

Wooliferkins

As a physicist then you know the maths and the data you need. As a failed GSE (no speling mistake youths) V, I & R muddled around . I think

dmch2

What i need is to do exactly as today but with the wind turned off and being in exactly the same state of fitness, thirst, hunger etc.

Then do both rides again when i'm 1, 2, 3, 4 and 5mph average fitter.

And repeat them all 5 times.

Then i can do all sorts of pretty graphs etc

Then it's ruined when some asks about a hillier or flatter route. So i'll have to do the same in Norfolk and the alps!

dilemna

dmch2 wrote:

What i need is to do exactly as today but with the wind turned off and being in exactly the same state of fitness, thirst, hunger etc.

Then do both rides again when i'm 1, 2, 3, 4 and 5mph average fitter.

And repeat them all 5 times.

Then i can do all sorts of pretty graphs etc

Then it's ruined when some asks about a hillier or flatter route. So i'll have to do the same in Norfolk and the alps!

You should get out more ...................... preferrably riding your bike.

I still maintained 18-20 mph into a 8-10mph WNW head wind for 24 miles this afternoon on my tourer with heavy rear panniers and bar bag. Just concentrate on your cycling technique maintaining a smooth cadence of 80-95 and not pushing heavy gears.

Peddle Up!

Watch out for the force nines!

http://www.bikeradar.com/forums/viewtop ... highlight=

bompington

danowat wrote:

After 9 months of commuting, all my data shows that with a tail wind my best time is 54mins, and with a headwind, the worst is 1:06.

Well after 3 years on a hilly 19 mile commute, my best time is 56 minutes, and worst is 1:45. The wind is responsible for almost all that, any gains (or at times losses) in fitness only seem to account for about 10 minutes variation in total.
Around here (east coast of Scotland) headwinds are actually more common than tailwinds on my commute. No, really, they are, particularly in summer - heading inland in the morning there's a land breeze, and by the time I head back towards the coast in the afternoon a sea breeze has picked up.

If you're really bothered, make sure and get accurate data for wind speed and direction, as we all know that subjective opinion is just a little bit prone to exaggerate: I use sites like this one

What gets me, quite apart from such geeky data recording, is my complete inability, despite years of gasping "the wind is my training partner" endlessly to myself, to feel happy about riding into a headwind - if we like to seek out hills to climb, why should headwinds be any different?

neeb

It's really impossible to generalise to get even an approximate estimate of how much difference a headwind will make unless you take into account lots of personal factors, especially position on the bike and technique. One thing I have really noticed as I have improved over the past 3 or 4 years is that I am better at maintaining a decent speed into a headwind, i.e. my average speed into a headwind seems to have increased disproportionately. I guess much of that is down to positioning and technique, i.e. learning how to get into a more aero position on the drops without losing so much power. I think when I was less experienced I was losing a lot of power whenever I tried to get aero due to not being able to recruit the same muscle power while in that position. Now I can push just as hard while tucked into the drops as when in a more upright position, and that makes a really big difference into a headwind.

Peddle Up!

Perception can be important too. I often think that a headwind has slowed me down, but a quick check on the speedo shows that I'm maintaining my usual speed.

softlad

Peddle Up! wrote:

Perception can be important too. I often think that a headwind has slowed me down, but a quick check on the speedo shows that I'm maintaining my usual speed.

in which case, logic (and physics) suggests either:

a) there is no headwind - or
b) you are simply increasing your power output to compensate

Peddle Up!

softlad wrote:

Peddle Up! wrote:

Perception can be important too. I often think that a headwind has slowed me down, but a quick check on the speedo shows that I'm maintaining my usual speed.

in which case, logic (and physics) suggests either:

a) there is no headwind - or
b) you are simply increasing your power output to compensate

b), of course, but I always feel that I'm going slower. Weird.