# How much does a 10mph head wind slow you down?



## Anders Moll (Jul 22, 2004)

How much does a 10mph head wind slow you down?

I average around 19-20 mph on a flat route with little or no wind.
In a 10 mph head wind I go 3-4 mph slower.

What is your expieriences?

Best Regards Anders


----------



## weiwentg (Feb 3, 2004)

Anders Moll said:


> How much does a 10mph head wind slow you down?
> 
> I average around 19-20 mph on a flat route with little or no wind.
> In a 10 mph head wind I go 3-4 mph slower.
> ...


4-5 mph slower for me - I'm a very light rider. I hate headwinds.


----------



## Kerry Irons (Feb 25, 2002)

*It depends*

Are we talking 10 mph on dead flat, completely open ground? Or is the road lined with houses and trees? Is the headwind absolutely straight head on, or is it off at an angle? Is it a steady wind or does it have some gusts? All of these factors have a big influence - just having a field of mature corn alongside the road can really cut into the power of a cross-head wind. You also should understand that you are not actually experiencing the 10 mph headwind - the wind speed gets lower and lower as you approach the ground and the 10 mph posted by the Weather Channel is taken about 30 ft above the ground and well away from any buildings or trees. Personally, I would say 2-3 mph rather than 3-4, but it's in that range.


----------



## PdxMark (Feb 3, 2004)

I would add that it depends on your base speed. Wind resistance goes up exponentially with speed. If you're normally riding 20 mph on the flats, I bet Kerry's 2-3 is about right. If you're soft pedaling at 12-13, you might not slow at all.


----------



## Einstruzende (Jun 1, 2004)

Here's an interesting read
http://w3.iac.net/~curta/bp/BikeSheet.html


----------



## Anders Moll (Jul 22, 2004)

*Conditions*



Kerry Irons said:


> Are we talking 10 mph on dead flat, completely open ground? Or is the road lined with houses and trees? Is the headwind absolutely straight head on, or is it off at an angle? Is it a steady wind or does it have some gusts? All of these factors have a big influence - just having a field of mature corn alongside the road can really cut into the power of a cross-head wind. You also should understand that you are not actually experiencing the 10 mph headwind - the wind speed gets lower and lower as you approach the ground and the 10 mph posted by the Weather Channel is taken about 30 ft above the ground and well away from any buildings or trees. Personally, I would say 2-3 mph rather than 3-4, but it's in that range.


I realiaze that I could have given a better describtion of the conditions. The 3-4 mph drop is in the worst case, as you describe, head on, in the open and with nearly no hills, not more than a couple 30 ft ones.
As you say, if there is just some small objects near the road slowing the wind, I agree with you, it is more like 2-3 mph.

By the way, do you have good easy way to determin if you are working against your self when you pedal. I sometimes suspect that I do, still pushing down sligtly when the pedal starts going upwards.

Best regards Anders


----------



## Fordy (Feb 3, 2004)

*No pilots here I guess.*

Thermal density is also a factor. That 10 mph headwind will slow you down more in the chill of winter than it will in the heat of summer.


----------



## terry b (Jan 29, 2004)

How did you determine it was actually 10 mph?

I think most people seriously overestimate the wind they encounter. I'm a weather nut with a pretty nice professional quality weather station on my house. I have a good sense of what winds are like, and I can say with some comfort that 10 mph is a darn stiff wind. As in bend over the bamboo in my yard stiff.

Last spring I brought my little hand held anemometer to an organized ride I do yearly. It's known for its bad winds. Stopped at one of the SAGs, and took some headwind measurements during a particularly bad blow. Some riders who had been struggling into it stopped to chat. I took a poll as to what they thought they were riding against. Answers - 10, 12, 15, 20. Reality - 4 mph gusting to 8.

To answer your question, a genuine, uninterrupted 10 mph wind slows me down from 20 to 12ish. Almost 50%. At least those are the results from times when I've had my Brunton handy and have taken the measurements. I guess I'm softer than everyone else.


----------



## AlexCad5 (Jan 2, 2005)

terry b said:


> How did you determine it was actually 10 mph?
> 
> I think most people seriously overestimate the wind they encounter. I'm a weather nut with a pretty nice professional quality weather station on my house. I have a good sense of what winds are like, and I can say with some comfort that 10 mph is a darn stiff wind. As in bend over the bamboo in my yard stiff.
> 
> ...


 Very interesting. As someone who grew up sailing, I often notice people overestimate the wind. Looking at your post, I overestimate it by quite a bit too.


----------



## terry b (Jan 29, 2004)

AlexCad5 said:


> Very interesting. As someone who grew up sailing, I often notice people overestimate the wind. Looking at your post, I overestimate it by quite a bit too.


I've been in discussions on this very board where people have said they have ridden home in thunderstorms producing 60 mph winds. I assume they got that number from the 11 o'clock news weather report, because one can barely stand in a wind like that. As a sailor, you must know the Beaufort Scale. It's an eye opener.

I know from personal experience that wind gusting across the road in the 8-10mph range is enough to take the bike out of your hands if you're daydreaming. (read - big lesson learned for me  )


----------



## Kerry Irons (Feb 25, 2002)

*My point exactly*



terry b said:


> How did you determine it was actually 10 mph?(


My point exactly. That 10 mph we get from the weather people is taken 30 feet above the ground and away from any obstructions. We know that the actual wind speed is zero at ground level. My guesstimate is that what we experience on the bike is something like 1/3 of the reported wind speed. So if the weather says 10 mph, we cyclists see 3 mph, and that kind of head wind knocks 19 mph down to about 16. Per terry b, a true 10 mph head wind (which might be 30 mph reported) would cut 19 mph down to about 10 mph. But that kind of wind would be VERY difficult to ride in, to say the least!


----------



## Bryan (Sep 19, 2004)

Kerry Irons said:


> Per terry b, a true 10 mph head wind (which might be 30 mph reported) would cut 19 mph down to about 10 mph. But that kind of wind would be VERY difficult to ride in, to say the least!


Sounds like beautiful, sunny spring days in Idaho!


----------



## terry b (Jan 29, 2004)

Bryan said:


> Sounds like beautiful, sunny spring days in Idaho!


And just about every day in New Mexico.


----------



## topflightpro (Nov 3, 2004)

Here in the south plains of Texas, I go by how fast the power wind mills are turning. I know they're above ground, but it's so flat here, there isn't much to obstruct the wind. It isn't uncommon to find myself having to fight the wind in my 6,000 pound truck as I drive to the grocery store. Plus, I know with my back to the wind, I go about 10 mph faster than going into the wind, but then again, I've got the wind to help push me along.


----------



## terry b (Jan 29, 2004)

Exactly. 

When I come home from work and my weather station (15' above the ground) is reporting 8-15 mph due to the summer evening thunder storms doing their stuff, I think long and hard about the kind of work-out I'm after. That kind of wind is no fun indeed. If the 10' tall stalks of Rio Grande Cane out by the barn are 45 degrees off of perpindicular, I know full well that I can expect to get the same on the bike.


----------



## GearDaddy (Apr 1, 2004)

Interesting indeed. Here in Minnesota we see consistent 5-10 MPH winds along with some more blustery days where winds are 20 MPH and gusting. But it's weird how on some days the wind may be reported as "light" but it seems to have more "power", and other days where the wind is reported to be stronger but it doesn't seem to be too bad at lower levels.

At any rate, I've found that the wind does not significantly affect a round-trip ride unless it's a particularly strong wind. Even then it only knocks down the average speed about 1 MPH. Into relatively strong headwinds you are working real hard to maintain 16 MPH, but with a tailwind you will be at 30+ MPH.

Ground cover definitely makes a big difference too. The spring around here (March, April, and May) are notorious for slow moving weather systems that produce strong easterly winds. But with no leaves on the trees, the wind truly does have more "fetch". Occasionally you end up in a steep 20 MPH+ headwind, where you're cranking as hard as you can just to go 10 MPH.

My golden rule of cycling is "Always have the wind at your back on the way home".


----------



## jimcav (Jun 15, 2003)

*i believe that is also offset by humidity.*

nothing more
jim


----------



## Anders Moll (Jul 22, 2004)

*Wind speed*



terry b said:


> How did you determine it was actually 10 mph?
> 
> I think most people seriously overestimate the wind they encounter. I'm a weather nut with a pretty nice professional quality weather station on my house. I have a good sense of what winds are like, and I can say with some comfort that 10 mph is a darn stiff wind. As in bend over the bamboo in my yard stiff.
> 
> ...


I did not actually measure the wind. It was just that one day I started wondering, I was on a little trip, about 60 km, and I thought, this is really tough. I noticed that sand from a construction site was flying, really had problems staying on the road. when I got home my average speed was about 4 mph lower than usually. Checked the current weather in my area on the internet, it said that the wind was 10-11 m/s that is 22-24 mph. I know that near the ground windspeeds are not as high as that, so I figured it was about the half.
Living in Denmark it is not hills or mountains that makes it tough it is the wind. I guess that half the time weather forecasts perdict windspeeds of 10mph or more.

Best regards Anders


----------



## rogger (Aug 19, 2005)

.....


----------



## Anders Moll (Jul 22, 2004)

*re*



rogger said:


> Same for Holland, 10mph is pretty standard stuff. It's best to go for a ride early in the morning, there's usually less wind to fight against.


I remember a couple of years ago there was a stage in tdf where the road was right out to the atlanticand there was a pretty strong wind, it did not take long before the peloton broke up into groups, like you see in the mountains.

Regards Anders


----------



## Matno (Jan 19, 2002)

It depends on whether the wind is blowing the same direction on the way back. I rode into a noticeable headwind yesterday. At 16 miles, my average speed was 17.3. Turned around and came back, and my average speed at 32 miles was 18.5. Some days I turn around and the wind has shifted and is a head wind again. So far, I've never experienced a tail wind in both directions! I did once get a steady tail wind on a one-direction ride though. Averaged just over 25mph for over 2 hours. I'm sure that's a best for me. It was SWEET until I realized we had taken a wrong turn and had to go back 10 miles with a strong headwind... :^(


----------



## BenWA (Aug 11, 2004)

*mmmm, depends...*



Kerry Irons said:


> My point exactly. That 10 mph we get from the weather people is taken 30 feet above the ground and away from any obstructions. We know that the actual wind speed is zero at ground level. My guesstimate is that what we experience on the bike is something like 1/3 of the reported wind speed. So if the weather says 10 mph, we cyclists see 3 mph, and that kind of head wind knocks 19 mph down to about 16. Per terry b, a true 10 mph head wind (which might be 30 mph reported) would cut 19 mph down to about 10 mph. But that kind of wind would be VERY difficult to ride in, to say the least!


This is generally correct, that is WHY many weather stations record wind velocity 30' above the surface: 10 m agl is generally a safe estimate for the top of the turbulent boundary layer that is affected by surface roughness and thermal turbulence in most places. 

Although Kerry I think your guesstimate might be a bit exaggerated for more open parcels with large fetches, few obstructions, and mostly laminar air flow. In such conditions, the decay in velocity due to surface friciton begins VERY close to the ground; a rider sitting 1 m above the surface may experience more than 90% of the wind velocity that is measured 10 m above the surface in this scenario. 


Fordy: yes sir, another pilot here!


----------



## tornado (Nov 26, 2004)

*Beaufort Scale for Wind Speed Estimation*

For some visiual clues as to what the wind actually is:

Beaufort Scale for Wind Speed Estimation
The Beaufort Wind Scale is named after Sir Francis Beaufort, an admiral in the British Navy. He developed the scale in 1805 in order to estimate wind speed by noting how sails move in the wind. It turned out to be a great help and was later adapted for use on land. 

Force 0 
Strength: Calm 
Speed: Less than 1 mile per hour (mph), less than 2 kilometers per hour (kph) 
Observations: Tree leaves don't move, smoke rises vertically, sea is calm 

Force 1 
Strength: Light Air 
Speed: 1-3 mph, 2-6 kph 
Observations: Tree leaves don't move, smoke drifts slowly, sea is lightly rippled 

Force 2 
Strength: Slight Breeze 
Speed: 4-7 mph, 7-11 kph 
Observations: Tree leaves rustle, flags wave slightly, small wavelets or scale waves 

Force 3 
Strength: Gentle Breeze 
Speed: 8-12 mph, 12-19 kph 
Observations: Leaves and twigs in constant motion, small flags extended, long unbreaking waves 

Force 4 
Strength: Moderate Breeze 
Speed: 13-18 mph, 20-29 kph 
Observations: Small branches move, flags flap, waves with some whitecaps 

Force 5 
Strength: Fresh Breeze 
Speed: 19-24 mph, 30-39 kph 
Observations: Small trees sway, flags flap and ripple, moderate waves with many whitecapes 

Force 6 
Strength: Strong Breeze 
Speed: 25-31 mph, 40-50 kph 
Observations: Large branches sway, flags beat and pop, larger waves with regular whitecaps 

Force 7 
Strength: Moderate Gale 
Speed: 32-38 mph, 51-61 kph 
Observations: Whole trees sway, large waves ("heaping sea") 

Force 8 
Strength: Fresh Gale 
Speed: 39-46 mph, 62-74 
Observations: Twigs break off trees, moderately high sea with blowing foam 

Force 9 
Strength: Strong Gale 
Speed: 47-54 mph, 75-87 kph 
Observations: Branches break off trees, shingles blown from roofs, hight crested waves 

Force 10 
Strength: Whole Gale 
Speed: 55-63 mph, 88-101 kph 
Observations: Some trees blown down, damage to buildings, high churning white sea 

Force 11 
Strength: Storm 
Speed: 64-74 mph, 101 kph-119 kph 
Observations: Widespread damage to trees and buildings, mountainous waves 

Force 12 
Strength: Hurricane 
Speed: 75 mph or greater, 120 kph or greater 
Observations: Severe and extensive damage


----------



## fast14riot (Jul 22, 2005)

> I think most people seriously overestimate the wind they encounter...Answers - 10, 12, 15, 20. Reality - 4 mph gusting to 8.


Well I do agree with this, but being a bowman and navigator/watch captain on some of the boats I race on, I am surprised that nobody has measured their _apparent_ wind speed while riding, i.e. wind felt only as a matter of moving through it. I would ask these same guys to subtract their ground speed from their guess and then see if they still think they are correct.

As a matter of fact the general public really has no way of quantifying perceived wind speed, unless you happen to be trained to pay attention to this; sailors, pilots, kite flyers, shooters/hunters, etc. I routinely check the weather stations for their wind forecast and am very surprised at the differences between them. Have you ever listened to the marine forecast for SF Bay in the summer? Winds 10 to 25 with gusts to 30 in the afternoon. I mean, jeez, this is a HUGE wind range, so I am not really surprised by great overestimation of wind speeds.

As far as how much you slow down in a head wind, don't forget to get down in the drops as this will help significantly. I don't know how many people I see riding into the wind on the flats and head up just mashing big gears to get through it when all you have to do is get down and aero to get throught it a bit quicker. I have noticed in IMO that TT wheels will help with riding into the wind as you dont have to keep fighting ultra light wheels to rountinely get them back up to speed, just spin 'em up and keep your head down.

Cheers-

P.S. the Bf scale really isn't used much in the US, at least by sailors, but is very popular in Europe.


----------



## CFBlue (Jun 28, 1999)

*Big Flat Ride and Winds*

I was on a T-Shirt ride this past weekend in the farmlands around Sacramento. I had expected to be able to maintain 23+ on the pancake flat course and was surprised at the struggle I had as the course changed directions through the orchards. The day before the wind was really howling...note scientific term for wind speed... so I was pushing it so I would finish the course early and miss the breeze I expected in the afternoon. Bike speeds were lower than I expected and I attributed it to the expected winds.

I was really surprised when I got off to find that there was just the lightest breeze, barely moving the leaves. that was a lot of self generated headwind. And it left me fresh out of excuses for why I didn't do better than 18.5 on a course with only 950 feet of climbing...(freeway overpasses). Had to be obeying the stop signs


----------



## Kerry Irons (Feb 25, 2002)

*Speed variations*



CFBlue said:


> I had expected to be able to maintain 23+ I didn't do better than 18.5


No offense, but this cracks me up. You expected to deliver around 250 watts, but you actually rode at 150 watts. For me, 18.5 mph is a relaxed pace, and 23+ is time trialling. That's like saying you expected to do a 1:05 25 mile TT, but instead you did 1:21. Either you totally don't know yourself or you had a REALLY bad day


----------



## Triker (Sep 27, 2004)

Here is the answer:

http://www.kreuzotter.de/english/espeed.htm


----------



## RodeRash (May 18, 2005)

Besides bikes, I fly kites at the beach -- power kites for mountain boards and kite buggies. Because the power generated by the "wing" (the kite is an airfoil) needs to be under control, it's important to have an accurate estimate of wind speed. 

A large kite can literally drag you down the beach on your face in a wind that's too strong. Sooooo, we have anonometers. But we also learn to look at the flags on buildings. It's possible to figure within a knot or two (knot = 1.1 MPH more or less) the wind speed from looking at the flags. 

Beauford uses movement of things in nature, but it's a long list. Flags and trees are pretty good guages and generally available. 

But too, about wind speed and where it's taken. Look at the tree tops next time you're in a gale. The wind is stronger up there than down on the ground. 

How much it slows you down sort of depends how aerodynamic you are. Wear a loose, baggy, flapping nylon shell sometime in a breeze. That slows you down more than wearing a skin-suit. Helmets, wheels, even the shape of the cranks, and surface of shoes will affect wind drag.


----------

