## Windspeeds?

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essjaydee
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### Windspeeds?

So in the aerospace world, if an aircraft is flying into a 15mph head wind and doing 65mph, its actual groundspeed is 65-15 = 50mph. Conversly if there was the same speed tailwind then 65+15 = 80mph.

Does this apply to cycling

Discuss.........

GiantMike
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### Re: Windspeeds?

If you're cycling at 10 mph you are covering the ground at 10 mph (assuming you're recording groundspeed). If you're riding at 10 mph into a 100kt headwind, you're travelling at 10 mph. It will feel like you're travelling at a combination of 10 mph road drag and 110 mph wind drag, but you're still travelling at 10 mph.
Last edited by GiantMike on Fri Nov 09, 2012 21:07 pm, edited 1 time in total.
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AchillesLeftKnee
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### Re: Windspeeds?

essjaydee wrote:Does this apply to cycling

Not really, no. Air speed in something that relies on aerodynamic lift is, if anything, analogous to the levels of mechanical grip available and the ability of the rider to maintain balance on a bike relative to ground speed.
Mangeur

morstar
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### Re: Windspeeds?

Put it another way. If the wind was gusting at 60 mph...

Do you think, with the wind to your back, you could ride at 60 mph + your normal cruising speed? e.g 75 - 85 mph or more if sprinting?

ddraver
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### Re: Windspeeds?

No, There are other things that slow you down. Yes it has an effect, and it has a larger effect the faster you go.

Put it another way, if you sit on the bike, pointing exactly downwind in a 30mph wind and don't pedal, do you move forward at 30mph or do you stay still and fall off?
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essjaydee
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### Re: Windspeeds?

ddraver wrote:No, There are other things that slow you down. Yes it has an effect, and it has a larger effect the faster you go.

Put it another way, if you sit on the bike, pointing exactly downwind in a 30mph wind and don't pedal, do you move forward at 30mph or do you stay still and fall off?

I'll give it a go and let you know

nweststeyn
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### Re: Windspeeds?

I fell off

entershikari
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Joined: Fri Jul 20, 2012 08:19 am

### Re: Windspeeds?

A plane has come inherently different forces acting on it than that of a bicycle. With a plane the only resistive force that acts upon it, slowing it down, is that of air resistance. This means that you can easily work out ground speed by adding the velocity of the wind to the velocity of the plane in relation to the wind.

But with a bicycle wind resistance is not the only force holding it back, there is rolling resistance and bearing friction. These need to be taken into account when considering the speed with a given wind direction.

Team4Luke
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### Re: Windspeeds?

essjaydee wrote:So in the aerospace world, if an aircraft is flying into a 15mph head wind and doing 65mph, its actual groundspeed is 65-15 = 50mph. Conversly if there was the same speed tailwind then 65+15 = 80mph.

Does this apply to cycling

Discuss.........

yes providing the plane does not increase it's power to return back to 65mph, same for a cyclist only we have resistance from the road/tyres and mechanical and bearing resistance also to overcome, something like 80% of your available power is needed just to push all this resistance out of the way before your remaining 20% can be used to propel your road speed. Can't remember the equation but to increase your speed by say 1mph the resistance against you increases fourfold, someone will come along and quote the maths.
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nickyboy zz
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### Re: Windspeeds?

wind resistance is proportionate to the square of the speed. So if you are travelling at 10mph and increase your speed by 10% to 11mph you will experience 21% more wind resistance 11x11/10x10

For your wind resistance to increase 4 fold you would need to increase your speed from 10mph to 20mph

renard
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### Re: Windspeeds?

With my aeroplane, I fly a bit faster than 65mph, but I fly at an airspeed, typically 250 knots at 10,000 feet.

I don't adjust my airspeed depending on the wind.

The groundspeed will alter, so with a headwind the flight will take longer and with a tailwind the flight will be shorter.

The effects of winds can't be simply additive.

If I am cycling along a road with a 20mph head wind I will be working hard to get home, but I will get there, even though I can't do 20mph on the flat in nil wind.

Equally if I had a 20mph tailwind and freewhelled, I would not do 20 mph on the flat. This would be because the wind force pushing me would eventually be balanced by the drag force, at a speed less than 20mph.

Ron Stuart
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### Re: Windspeeds?

essjaydee wrote:So in the aerospace world, if an aircraft is flying into a 15mph head wind and doing 65mph, its actual groundspeed is 65-15 = 50mph. Conversly if there was the same speed tailwind then 65+15 = 80mph.

Does this apply to cycling

Discuss.........

Answer is your premise is wrong as GiantMike has pointed out although unlike the aircraft with a bicycle there is more to resist movement than just air resistance there is also rolling resistance.

So " Does this apply to cycling" exact answer would be no.

By the way one knot equals one nautical mile which equals 1.852 km/h and can be converted to 1.151 mph. So the formula would work out like this 10 knots X 1.151=11.51 mph.

Another aside is that the speed of sound varies with the density of air ( or whatever material it is transmitted through). Density of air has a bearing on cycling world record attempts ( the famous hour record in Mexico City ) fast times in a Velodrome can be aided by ( Low Pressure Weather ).

So a 20mph head wind at 5C would have the effect of slowing you down more than a 20mph head wind at 20C this is because the cold wind has a greater density and therefore more inertia.