How Do I Quantify Wind?

I was sitting back riding at 20mph during a solo ride and over a fairly flat mile with my cadence the same and my speed the same my power output ranged from 130w to 250w. Minor changes in gradient make a big difference in speed.

I would say don't worry about it. Keep track of your time over a route that you do a lot. Try to lower your time each time you do that route. Chasing the clock will improve you more than compensating for the wind.

You can't really do intervals based on a set speed or a time over a given distance in the "real world" like you can on a trainer. You intervals should be based off of effort over a given time. If you are using a PM then it is based off of wattage, HR monitor HR, neither then PE, this takes real world variances (wind, hills, etc.) out of the equation. I never really even look at speed or distance, it is all based off of effort and time.

There are just far to many factors to come up with some formula, like road surface, your body size, riding position, equipment, etc.

Thanks for the info. What is PE?

Perceived Exertion I believe is what he was saying.

I agree with bgoetz. Don't base it off speed or distance. Focus on the effort over time. We get some wicked wind here in the Dallas area. I can be going 30mph with the wind and 12 against it - it's horrible. I use a power meter so I just keep the same wattage and cadence for my interval regardless if I'm heading into the wind or riding with it. Depending on the wind strength, it can sometimes be hard to maintain higher watts with a tailwind.

If you have a HR monitor, you just keep the HR at the zone you are training for your interval. Keep in mind that it will take several minutes for HR to come up so try not to start out too hard. Over time, you will get a feel for how hard to push for different types of intervals.

If you are just going by perceived exertion, just try to hold it at a certain range for your interval.

Trying to see if you get faster over a given course is great, but environmental conditions such as wind and temperature will affect performance. If you are logging your workouts and trying to go for a new personal record over that course, always look at the weather and record temperature and wind speed. If you don't, you may get frustrated to find that with greater fitness you are slower. Wind can have a DRAMATIC effect on speed.

On the topic of wind and hills, I read someone in another forum say: Hills make your stronger, but wind makes you mean.

I have yelled so many profanities at the wind on some of my rides [IMG]/img/vbsmilies/smilies/smile.gif[/IMG]

Here's some stuff I jsut found on the net. Man, you ain't kidding about wind affecting speed. From my calculations it looks like you drop from 20 mph to about 17 mph riding into a 5 mph headwind. that's more of a drop than I expected but it explains why I suck so bad in the wind. Can someone check my math?

Power requiredThere is a well known equation that gives the power required to push a bike/rider through the air and to overcome the friction of the drive train:

P=gmVg (.0053) + VgVaVa(.185)

Where P is in watts, g is Earth's gravity, Vg is ground speed (m/s), m is bike/rider mass in kg, s is the grade (m/m), and Va is the rider's speed through the air (m/s). K1 is a lumped constant for all frictional losses (tires, bearings, chain), and is generally reported with a value of 0.0053. K2 is a lumped constant for aerodynamic drag and is generally reported with a value of 0.185 kg/m.

I used 82kg and (1 mph = 0.45 m/s).

Quoted post said:

Originally Posted by Jim Moore [IMG]/img/forum/go_quote.gif[/IMG]

Here's some stuff I jsut found on the net. Man, you ain't kidding about wind affecting speed. From my calculations it looks like you drop from 20 mph to about 17 mph riding into a 5 mph headwind. that's more of a drop than I expected but it explains why I suck so bad in the wind. Can someone check my math?

Power requiredThere is a well known equation that gives the power required to push a bike/rider through the air and to overcome the friction of the drive train:

P=gmVg (.0053) + VgVaVa(.185)

Where P is in watts, g is Earth's gravity, Vg is ground speed (m/s), m is bike/rider mass in kg, s is the grade (m/m), and Va is the rider's speed through the air (m/s). K1 is a lumped constant for all frictional losses (tires, bearings, chain), and is generally reported with a value of 0.0053. K2 is a lumped constant for aerodynamic drag and is generally reported with a value of 0.185 kg/m.

I used 82kg and (1 mph = 0.45 m/s).

No.

First, the units are all wrong, assuming the constants (K1 and K2) are unitless. Units of power are kg∙(m^2)/(s^3), i.e. watts. Your first term yields units of kg∙(m^3)/(s^5), while your second term gives units of (m^3)/(s^3).

Second, in a simple model you would use the resultant velocity, V=Vb+Vw[cos(θ)], where Vb is the velocity of the bike, Vw is the velocity of the wind, and θ is the angle between the direction of bike travel and the wind. If the wind is blowing in a direction opposite the bike, Vw is negative. Likewise, if the wind is blowing in the same direction of bike travel, Vw is positive.

Third, the forces to overcome will be:
--bearing drag (can apply to chain too) and rolling resistance
--aero drag
--gravity (only if on a slope)

Power relates to force by P=F∙V.

The power needed to overcome gravity will then be P=mgVb[sin(θ)], where m is mass, g is the acceleration of gravity, and θ is the angle of the road to the horizontal.

The power needed to overcome drive train losses, bearing losses, and rolling resistance will be P=mgVb(Crr+Ct+Cb)cos(θ), where Crr is the coefficient of rolling resistance, Ct is the coefficient of drive train resistance, and Cb would be coefficient of bearing resistance.

The power needed to overcome aero drag will be P=ρACdV^3, where ρ is the air density, A is the area presented to the wind, Cd is the coefficient of drag, and V is as defined in the second paragraph.

Again, that's a simple model. Cd will actually change depending on the direction of the wind and the position of the rider on the bike.

Perhaps the best thing to do, if you really want to do this the simple way, is use Analytic Cycling's "Wind on Rider" calculator to see how different performance metrics vary with wind speed and direction. Here's the link: http://www.analyticcycling.com/DiffEqWindCourse_Page.html .

I have a quick calculator mounted on top of my garage. One look up and I can plan my ride taking full advantage of tail wind. Cycling is fun.[IMG]/img/vbsmilies/smilies/smile.gif[/IMG]

[IMG]cyclingforums.com160Open ↗[/IMG]

Yes, PE is perceived exertion. And I think Alienator's mathematical breakdown (impressive breakdown if it is accurate BTW), is a prime example of why you cannot really target a speed or time over a given distance if you when doing intervals, there are just to many factors. Even a very impressive calculator will not get you as close to a set power output as using HR and maybe even PE, and certainly will not be as close as using a PM. A calculator will also not factor in changes in wind speed (wind is not a constant mph) and wind direction (you as well as the wind will likely change direction throughout the ride), so again base your intervals off of effort over a given time.

Alienator, good stuff. But on your formula for drivetrain losses, what's theta?

Since gravity has an effect while riding hills and to a lesser extent on the flats, you guys need the variation of the gravitational coefficient. It changes based on altitude - it is slight, but definitely measurable to the .0000001 Newtons.

Also, the position of the moon affects the net gravitational pull of the Earth on bodies.

Actually, all the planets and stellar objects have an effect. What's hard to account for are those singularities out there we can't see.

A bigger rider in front of you will not only block more wind, he will actually try to pull you with gravity.

And, if you ride fast enough, you can actually orbit the Earth close to ground level, but there are problems with friction/heat. But, that would completely negate the effects of Earth's gravity.

[IMG]/img/vbsmilies/smilies/biggrin.gif[/IMG]

I'm sorry. I couldn't resist. I like numbers too actually. I think sometimes you just gotta ride the bike. I say all this in jest.

Get an iBike.

Quoted post said:

Originally Posted by Jim Moore [IMG]/img/forum/go_quote.gif[/IMG]

Thanks for the info. What is PE?

Premature Emasculation... A condition that usual occurs in cycling when one complains too much about the wind and/or the hills.

:P

🙂

Quoted post said:

Originally Posted by dhk2 [IMG]/img/forum/go_quote.gif[/IMG]

Alienator, good stuff. But on your formula for drivetrain losses, what's theta?

It's the angle of the ground to the horizontal.