Wind power

Borderfox

Just curious and there seems to be some serious maths head on the forum

If I am cycling at 30kmph into a 30kmph headwind what speed does that bring the headwind up to? been out a good few time in something similar and the headwind (without gusting) feels a lot stronger like 2x stronger. Not too good on the math end of things so just trying to quantify the feeling

Zen0

IIRC the apparent wind speed doubles to 60kmph, but the effort required to overcome the increased wind resistance quadruples. That's because your profile into the wind is a two dimensional surface, so the resistance increases as the square of the increase in the resistance force.

nilhg

Borderfox wrote: »

Just curious and there seems to be some serious maths head on the forum

If I am cycling at 30kmph into a 30kmph headwind what speed does that bring the headwind up to? been out a good few time in something similar and the headwind (without gusting) feels a lot stronger like 2x stronger. Not too good on the math end of things so just trying to quantify the feeling

The apparent wind speed to the rider will be 60km/hr, the problem is that as wind resistance (the effective wind speed in your face) doubles the power needed to maintain a constant speed quadruples, so the figures don't be long ramping up.

To use your example above, on a calm day at 30km/hr a rider might be putting out 175watts, into a 30km/hr headwind that rises to over 500watts. All figures from the Bike Calculator, try putting some figures in and sliding the red dot back and forth to get an idea for yourself.

http://bikecalculator.com/what.html

Borderfox

That's a great calculator, thanks for the responses

magicbastarder

i guess it's easiest to use aviation terms - ground speed and airspeed?

smacl

magicbastarder wrote: »

i guess it's easiest to use aviation terms - ground speed and airspeed?

I think that relates more to extra distance that must be travelled at altitude due curvature on the earth. Doesn't really relate to bike unless you have you're saddle really high

triggermortis

smacl wrote: »

I think that relates more to extra distance that must be travelled at altitude due curvature on the earth. Doesn't really relate to bike unless you have you're saddle really high

No. Airspeed is the relative speed of an aircraft through the airflow and ground speed is the speed it is moving over the ground, so it's an accurate analogy

smacl

triggermortis wrote: »

No. Airspeed is the relative speed of an aircraft through the airflow and ground speed is the speed it is moving over the ground, so it's an accurate analogy

My bad, every day's a school day.

el tel

It's very simple, if you are cycling at 30kmph into a 30kmph headwind, that means your net speed is 0mph, and you fall over, or do a trackstand.

magicbastarder

if you're cycling forwards at 30km/h on a treadmill moving backwards at 30km/h, and it's sitting on a truck driving forwards at 30km/h, and a fan is blowing into your face at 30km/h, but there's a 30km/h tailwind, how fast are you going?

Lumen

Zen0 wrote: »

IIRC the apparent wind speed doubles to 60kmph, but the effort required to overcome the increased wind resistance quadruples. That's because your profile into the wind is a two dimensional surface, so the resistance increases as the square of the increase in the resistance force.

Careful now.

The drag force of the headwind quadruples with a doubling of air speed, but the energy requirements are determined by force x distance, and the power requirements are determined by force x ground speed.

For this reason cycling at 30kph into a 30kph headwind is NOT the same as cycling at 60kph with no headwind. Otherwise, there would be an amount of headwind at which you can't cycle forwards at all, and that is not true. Theoretically you can cycle into a 200kph headwind, just very, very slowly.

el tel

I ca

Lumen wrote: »

Zen0 wrote: »

IIRC the apparent wind speed doubles to 60kmph, but the effort required to overcome the increased wind resistance quadruples. That's because your profile into the wind is a two dimensional surface, so the resistance increases as the square of the increase in the resistance force.

Careful now.

The drag force of the headwind quadruples with a doubling of air speed, but the energy requirements are determined by force x distance, and the power requirements are determined by force x ground speed.

For this reason cycling at 30kph into a 30kph headwind is NOT the same as cycling at 60kph with no headwind. Otherwise, there would be an amount of headwind at which you can't cycle forwards at all, and that is not true. Theoretically you can cycle into a 200kph headwind, just very, very slowly.

You think? I want to see someone manage to cycle forwards into a headwind of say, 370kmh.  I'd say there are both theoretical and practical limits.

Chips Lovell

I'm volunteering Beaker for this experiment.

mamax

When I'm cycling into a headwind at 30kph I wish strava would re-calculate my average speed to show there was no headwind :rolleyes:

Lumen

el tel wrote: »

You think? I want to see someone manage to cycle forwards into a headwind of say, 370kmh.  I'd say there are both theoretical and practical limits.

Practically the problem is (I think) going to be that the centre of pressure is higher than the rear wheel skewer, so at some point you flip over backwards. :pac:

Chips Lovell

magicbastarder

el tel wrote: »

I ca

You think? I want to see someone manage to cycle forwards into a headwind of say, 370kmh.  I'd say there are both theoretical and practical limits.

it's just about getting *really* aero.

Thud

el tel wrote: »

I ca

You think? I want to see someone manage to cycle forwards into a headwind of say, 370kmh. I'd say there are both theoretical and practical limits.

Dutch are all over this...
http://www.cyclingweekly.com/news/racing/watch-riders-battle-100kph-winds-dutch-headwind-championships-301112

tuxy

This is one reason for buying a power meter, you can look at your power into the headwind and feel happy as apposed to looking at your speed and feeling depressed.

Beasty

Is it 42???

Lumen

tuxy wrote: »

This is one reason for buying a power meter, you can look at your power into the headwind and feel happy depressed as apposed to looking at your speed and feeling depressed.

Fixed that for you.

Daroxtar

positron

magicbastarder wrote:

if you're cycling forwards at 30km/h on a treadmill moving backwards at 30km/h, and it's sitting on a truck driving forwards at 30km/h, and a fan is blowing into your face at 30km/h, but there's a 30km/h tailwind, how fast are you going?

Depends on what colour your bike is and what you are smoking. Can I have some?

NeedMoreGears

At 30kph in still air, I would be putting out about 180watts. If I take that mighty wattage out in a 370kph wind, apparently I could manage 0.25kph. At 30kph I would typically using at 50/19 combination. All I'd need to for the 370kph wind would be a 50/2280 - so I could still look cool at 90rpm.

This is where things could start to get tricky. A 2280 ring would probably be around 10m in diameter so I wouldn't be able to reach the handlebars and I'd be a bit worried that rear wheel of that size would get blown around a bit. I am also pretty bad at trackstands so I wouldn't be over confident of my balance at that sort of speed.

Maybe a day for the wimp list.

CramCycle

NeedMoreGears wrote: »

This is where things could start to get tricky. A 2280 ring would probably be around 10m in diameter so I wouldn't be able to reach the handlebars and I'd be a bit worried that rear wheel of that size would get blown around a bit. I am also pretty bad at trackstands so I wouldn't be over confident of my balance at that sort of speed.

Maybe a day for the wimp list.

You could have one of those systems they had where your rear cog that you push is actually spinning a larger cog at the same rotational speed, which in turn is spinning a really small cog on the wheel (you could add a few more steps in to increase this). The bike would weigh a ton though and the power to get it to move would be colossal.

Lumen

CramCycle wrote: »

You could have one of those systems they had where your rear cog that you push is actually spinning a larger cog at the same rotational speed, which in turn is spinning a really small cog on the wheel (you could add a few more steps in to increase this). The bike would weigh a ton though and the power to get it to move would be colossal.

Source: http://www.popularmechanics.com/adventure/sports/a22837/world-speed-record-riding-a-bicycle-147-mph/