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Calculating windchill...

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Calculating windchill...

01-17-20, 07:01 PM
#26
AllWeatherJeff
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Originally Posted by DrIsotope
Oh, for sure. I mean, traveling 25mph into a 25mph wind on a bicycle would take something between 1,700 and 2,000 watts. You'd be producing so much heat you could take your shirt off.

The windchill (relative) is as I said much earlier, around 5ºF, give or take. That's cold. If the wind chill were recalculated to say, -1ºF, would that make an earth-shattering difference?
It actually does.

Especially when you have to stop, and the sweat trapped beneath winter layers gets cold really fast. If you stop for too long it can be impossible to get warm again until you get home.
01-17-20, 07:02 PM
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AllWeatherJeff
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Originally Posted by Marcus_Ti
Look up the windchill equation .... it is a rather hilarious exercise of "why in the world is that the case???!!!"

The formula for calculating windchill, as I understand it, is for a stationary body. No?
01-18-20, 10:45 AM
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Originally Posted by AllWeatherJeff
It actually does.

Especially when you have to stop, and the sweat trapped beneath winter layers gets cold really fast. If you stop for too long it can be impossible to get warm again until you get home.
I always carry some spare layers and spare pair of gloves or mitts when I am doing a longer duration ride in very cold temps. If I get too warm I stop and take a layer off, if I start feeling too cold I stop and put a layer on...Hands is the hardest part to keep warm on long duration rides in cold weather... My experience has been that once your gloves get soaked with sweat and your hands get too cold it becomes very difficult to re-warm them unless you put on a fresh pair of dry gloves.
01-18-20, 10:56 AM
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Originally Posted by Marcus_Ti
Look up the windchill equation .... it is a rather hilarious exercise of "why in the world is that the case???!!!"
You'd be amazed how much of engineering is still like this. Especially in fields like aerospace where all the fundamental research was done 100 years ago
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01-18-20, 12:25 PM
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Originally Posted by Darth Lefty
You'd be amazed how much of engineering is still like this. Especially in fields like aerospace where all the fundamental research was done 100 years ago
Windchill is barely 50 years old though, and the models used now are not even 20...originally (pre-WW2) it was far less "engineering" and instead, "stick a water bottle outside and how much less time does it take to freeze in the wind versus static air".

https://en.wikipedia.org/wiki/Wind_chill#Original_model
01-18-20, 12:46 PM
#31
u235
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I don't know the actual wind chill or the "feels like" math and exact equations but if you are standing still in a 50mph wind compared to going 50 mph on your bike in a zero wind, it is the exact same effect of cooling by wind passing your body. It doesn't matter which one of the two is moving and which one is stationary relative to the surface of the earth. The wind chill concept relates to the laminar boundary layer around the surface of your skin. The more colder wind, the lower the temperature just above the surface of your skin is because the relative warm air radiated is whisked away. The bigger difference in surface temperature compared to the temperature right above the surface causes the body to lose more heat faster. Hairy people are less impacted by wind chill for the same exact reason they are less aerodynamic on a bike. Wet suit in the water is another example of reducing "wind chill" but in the water. The suit material is not the primary thing keeping you warm as an insulation, the suit is trapping "warm" water near your skin reducing the heat loss. In air.. the more coats and layers you have on the less the impact. Water has a higher specific heat capacity than air and can also conduct heat much faster similar to a wind chill, that is why you are colder when you are wet even at the same actual temperature. 70 degrees in your house is comfortable but a 70 degree shower can be really cold. Same concept as touching a 20 degree piece of cork bar tape compared to touching a 20 degree piece of aluminum. The aluminum will FEEL colder but it is not. It's pulling more heat from your fingers just like a heavy wind would.
In the end. Your skin can't sense specific "temperature" very well, it is good at sensing the rate of change of that temperature. Cold wind passing by increases the rate. They attempted to standardize a generic average set of conditions with wind and use that. Wind chill factor

Last edited by u235; 01-18-20 at 09:54 PM.
01-18-20, 12:54 PM
#32
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Originally Posted by wolfchild
.. My experience has been that once your gloves get soaked with sweat and your hands get too cold it becomes very difficult to re-warm them unless you put on a fresh pair of dry gloves.
Neoprene gloves as liners are a great solution to keep your outer gloves dry. Your hands will be pruned at the end of a long ride, but the neoprene keeps keeps the gloves from getting soaked so your hands stay warm (though wet). Disposable, Powder free, examination gloves work great as liners too, and can also be rinsed an re-used for many rides.

With liners you don't have to carry an extra pair of gloves, but it's a good idea to carry a spare pair of liners.
01-23-20, 08:56 AM
#33
Notso_fastLane
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Originally Posted by AllWeatherJeff
My understanding is that this is the formula for determining windchill for stationary objects.

What I'm unsure of is if bike velocity and windspeed can be combined by simple addition to determine windchill "in motion", or if there is an exponential factor to consider as when two cars collide head on.
For simplicity sake, this is correct.

More accurately, wind 'speed' is a velocity, and they are added as vectors, i.e. direction and magnitude are both important. If you are going exactly into the wind, it is simply added to your speed, if you are travelling exactly with the wind, it is subtracted, to get the relative wind air velocity.

When two cars collide head on, each traveling at 15mph, the force of their collision is not the sum total of their combined velocities. Is it not the same when riding into a headwind?
This is partially correct. In a collision (which is different, from a physics perspective), you have momentum, and you have kinetic energy. Momentum is linear (mass x velocity) and energy is non-linear (mass x velocity^2).
Originally Posted by DrIsotope
If your relative velocity is slower than the windspeed, the wind is never going to be hitting you faster than the wind is blowing.

If the wind speed is 20mph and your speed is 10mph, the wind speed is 20mph.
If the wind speed is 10mph and your speed is 20mph, the wind speed is 20mph.
This is incorrect. As noted above, wind speed is technically a velocity vector, and is handled with vector arithmetic.
Originally Posted by AllWeatherJeff
Thanks. I wasn't sure if there was some kind of exponential factor of momentum nvolved as when two cars collide head on.
I hope I cleared this up.

A standard wind chill chart will be accurate for judging the relative temperature. I just assume, because the wind is too variable, a standard 20 mph wind to take into account typical speeds and variable winds, to judge what to wear. I recommend the NOAA chart, since it's easy to read and decipher.

Note that the differences in relative temperature don't go down very quickly relative to the speed (vertical axis), but they do go down more quickly relative to the temperature. This is why just using 20 mph as a ballpark figure is pretty reasonable. The difference between 20 mph and 40 mph at 15F is only 6F (-2 to -8).

https://www.weather.gov/safety/cold-wind-chill-chart

Background: I'm an aerospace engineer with a background in thermodynamics, so I used to do this stuff a lot (now I'm more of a structures specialist).
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01-23-20, 09:47 AM
#34
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What I want to know is why the weather peeps don't give us the "wind chill" in the summer? Even in hot weather the wind cools our body down, that's why people use fans. That's why we feel cooler on a moving bike than one stopped at a red light.

Instead, they only give us the heat index based on humidity. (which of course is also real) It's a scam to keep us feeling miserable, I tell ya.
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01-23-20, 10:03 AM
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AlmostTrick There's a limit to that, at some level it's hot enough it's like riding in a blast furnace.

I think lots of people believe weather forecasts are overstated to play it safe. Sometimes when they talk about likelihood it's easy to misunderstand. Percent chance of rain is a good example, you need to combine it with the predicted amount to have decent meaning. Similar problems with "percent contained" fires and hurricane direction cones
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01-23-20, 10:14 AM
#36
Notso_fastLane
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Originally Posted by AlmostTrick
What I want to know is why the weather peeps don't give us the "wind chill" in the summer? Even in hot weather the wind cools our body down, that's why people use fans. That's why we feel cooler on a moving bike than one stopped at a red light.

Instead, they only give us the heat index based on humidity. (which of course is also real) It's a scam to keep us feeling miserable, I tell ya.
Do you really want to know, or are you just being snarky? Nothing wrong with snark, just don't want to type up a long answer if you're just blowing hot air.(see what I did there?)
01-23-20, 10:23 AM
#37
AlmostTrick
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Originally Posted by Notso_fastLane
Do you really want to know, or are you just being snarky? Nothing wrong with snark, just don't want to type up a long answer if you're just blowing hot air.(see what I did there?)
Both. I believe it's a valid question for the reasons I stated.

"Even in hot weather the wind cools our body down, that's why people use fans. That's why we feel cooler on a moving bike than one stopped at a red light."
01-23-20, 11:01 AM
#38
Notso_fastLane
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Originally Posted by AlmostTrick
Both. I believe it's a valid question for the reasons I stated.

"Even in hot weather the wind cools our body down, that's why people use fans. That's why we feel cooler on a moving bike than one stopped at a red light."
You are partially correct. This works in a dry (<30% relative humidity) environment.

The reason is that when liquid evaporates, it is absorbing energy (latent heat of vaporization). We feel that absorption as cooling. Unfortunately, once the humidity gets too high, not enough evaporation goes on, and you just get moist.

Our environmental body temperature (as opposed to our core temperature) is right around 89F. This means at 89F, if you aren't really doing anything, your body's heat output/input would be balanced. However, our bodies are always "doing something"....they are metabolizing and constantly generating heat. That's why our actual comfort zone is much lower.

If you look at the chart I linked to above, it doesn't even start until 40F and colder. The chart assumes a few things: 1) we aren't running around outside naked; 2) we have some control over how long we are exposed to wind/cold.

An exposed (naked, essentially) human can stand temps down to about 60F indefinitely. It's chilly, but you won't die unless you are exposed for really long (like longer than you would need to die of dehydration or starvation anyway). Above that, and up into about the mid 80s, you're pretty much safe from any kind of temperature related effects unless you're really exerting yourself.

Once you start getting warmer, you run the risk of overheating, so again, the warnings only start when it gets to the point where it can happen quickly enough that you are reasonably likely to pass out/die before you can get into cover or get cooled off.

Since you have some motorcycling background, here's an interesting tidbit: In the summer, in a dry environment, if you wear light colored leathers or MC specific clothing with some ventilation, you will stay cooler than that the full mesh riding gear that is so popular. I used to ride my CBR in AZ all summer long and I would always wear my leathers. It sucked if I was in traffic, but I generally use that bike for fun rides, and not commuting. [/i]
01-23-20, 11:22 AM
#39
Notso_fastLane
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I'm putting this slightly more technical discussion here, so if you aren't at all interested in thermodynamics or heat transfer, just skip this one (I won't throw any math at you though, so no worries there).

There are 3 types of heat transfer modes that we discuss in thermodynamics:
2) Conduction
3) Convection

Radiation is what you feel when you step from the shade into direct sunlight, or turn a heat lamp (or incandescent lightbulb) on. This is why for the same given air temperature (remember, official air temperatures are always taken in the shade) you can be much warmer when riding on a clear day than on an overcast day.

Conduction is what you get when you put two object at different temperatures in direct contact. Heat (energy) always flows from the hotter object to the colder object. There is very little conduction going on in most of what we do as cyclists that we can do anything about. But it is important in a way that will be described below.

Convection is the transfer of heat away from a body by a medium (air, water, coolant, etc) that is temporarily in contact with that object, but is flowing. Even in "stationary" (no wind) air, there is a significant amount of actual air motion and convection going on. This is what we experience as wind chill in cooler temperatures.

All the things we do to regulate temperature on a bike are mostly about mitigating (or enhancing) convection. Cold? Wear a jacket. The jacket provides direct thermal insulation by preventing or reducing the convection of the air on your skin. A well made "breathable" jacket (or pants/tights) allows just enough air circulation to allow evaporation without excessive cooling. These garments also provide conductive and radiative insulation between your skin and the colder environment (this is why some materials use things like aluminum, to reflect the radiation part of heat back to you. I have insoles that do this, very well mind you!). As noted before though, the convection component is the largest heat loss, so that is primarily what cold weather clothing targets.

One of the most notable items in your wardrobe that is conductive are you bike shoes. If you don't have insulated, winter specific shoes (or very good insoles), most bike shoes are simply hard plastic with a metal cleat. That metal cleat is in direct contact with your pedals. That is essentially a significant, and pretty efficient, conductive heat sink (metal is something like 10-50 times more efficient at conducting heat than plastic/air). The best insulation generally needs to be between your foot and the sole of the shoe, although covers help as well, since they reduce the convective losses for the rest of the shoe.

Flip side of some of this, that goes against common thought: in hot dry weather, you will stay cooler if you wear slightly looser light colored clothing that completely covers you (think desert nomads!). The light color reflects the sun (reducing the radiation effects), the looser clothing allows your body's sweat to form a slightly more humid micro environment that can enhance the evaporative cooling effect. Note that this must allow some convection within the confines of the clothing, or the cooling effect happens a few feet behind you. That's why you want the evaporation to happen within your bike clothing...some internal circulation is needed. That's why vented is better than mesh.
01-23-20, 11:30 AM
#40
u235
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Originally Posted by AlmostTrick
Both. I believe it's a valid question for the reasons I stated.

"Even in hot weather the wind cools our body down, that's why people use fans. That's why we feel cooler on a moving bike than one stopped at a red light."
They do combine both concepts, the "feels like temperature". In theory covers both wind chill and the heat index for both extremes.
The wind chill concept is not the major player of what cools you in the heat, evaporation of sweat is. Wind plays a role in evaporation but in a different way than wind plays a role when it is really cold out. Totally different set of equations and calculations with humidity. A little extreme but you can still be cooled down by a 105 degree wind even though that wind is actually warmer than your body temperature. Stop sweating or run out of fluids and things go bad QUICK. The heat index or the feels like takes temperature/humidity into account but not wind. We think of sweat as looking down and seeing water on your skin, you sweat to remove heat and it is happening all the time but not always enough to see it build up.

Just rambling here.
One thing I learned pretty quick... I ride a lot of rolling terrain, it is either up or down. If I am going to take a break it is very tempting to do it at the peak of a climb. For heating and cooling that is the worst possible time. When you stop at the top your body is creating the max amount of heat and you no longer have the wind cooling, the sudden "stopping at the red light" situation. Done with your break or pause you proceed down the other side. Much less heat being generated and full on wind cooling and you probably built up sweat from the stopping before. When it's warm out anyway this is usually not a problem but any sweat buildup when it is under say maybe 50-60F (depends on the person and clothes) and it can create a condition that is hard to recover from as the ride continues. It is similar to wearing a wind breaker starting in the cold morning as the day gets warmer. You can unzip, open up arm pits etc but at some point you have to take it off and suffer 5-10 minutes of being really cold in certain spots until you equalize again. Proper specialized clothing can mitigate some of this but not all of it. Getting way off topic here but I find rolling through the woods and hills on an MTB to be a FAR higher potential for overheating, even worse than being stopped on 150F asphalt on a road bike. You are moving at slower speeds for the same level of effort and wind cooling is negligible. Coupled with there is usually much less natural wind deep in the trails and the humidity is higher in the woods, at least you are not in direct sun but it can be brutal just stewing in that sauna and no potential to eventually open it up and cool off.

Last edited by u235; 01-23-20 at 02:50 PM.
01-23-20, 01:57 PM
#41
AlmostTrick
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Wow, lots of interesting info, Not so fast. I learned a few things today. Thanks!

I'm gonna zero in on one comment, because I have a question for you.

Originally Posted by Notso_fastLane
One of the most notable items in your wardrobe that is conductive are you bike shoes. If you don't have insulated, winter specific shoes (or very good insoles), most bike shoes are simply hard plastic with a metal cleat. That metal cleat is in direct contact with your pedals. That is essentially a significant, and pretty efficient, conductive heat sink (metal is something like 10-50 times more efficient at conducting heat than plastic/air). The best insulation generally needs to be between your foot and the sole of the shoe, although covers help as well, since they reduce the convective losses for the rest of the shoe.
I've noticed the "heat sink" effect of cycling shoes with metal cleats. Non cycling shoes of similar construction on platform pedals are noticeably warmer when temps get down to freezing and below. Is there any way to effectively insulate that steel plate in the cycling shoe?
01-23-20, 02:06 PM
#42
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Originally Posted by u235
One thing I learned pretty quick... I ride a lot of rolling terrain, it is either up or down. If I am going to take a break it is very tempting to do it at the peak of a climb. For heating and cooling that is the worst possible time. When you stop at the top your body is creating the max amount of heat and you no longer have the wind cooling, the sudden "stopping at the red light" situation. Done with your break or pause you proceed down the other side. Much less heat being generated and full on wind cooling and you probably build up sweat from the extreme. When it's warm out anyway this is usually not a problem but any sweat buildup prior when it is under say maybe 50-60F (depends on the person and clothes) and it can create a condition that is hard to recover from as the ride continues.
So where do you stop? Part way up the hill is my guess. (allow yourself to coast until you're near stopped) Surely you wouldn't waste energy and brake at the bottom!
01-23-20, 02:11 PM
#43
Notso_fastLane
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Originally Posted by AlmostTrick
Wow, lots of interesting info, Not so fast. I learned a few things today. Thanks!

I'm gonna zero in on one comment, because I have a question for you.

I've noticed the "heat sink" effect of cycling shoes with metal cleats. Non cycling shoes of similar construction on platform pedals are noticeably warmer when temps get down to freezing and below. Is there any way to effectively insulate that steel plate in the cycling shoe?
I bought a pair of winter cycling specific shoes (Fizik Artic). In addition, I added some insoles. The insoles by themselves helped a little in my regular shoes, but 1) not enough for me, and 2) my regular shoes don't really have the room for them. My winter shoes are one size larger.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
01-23-20, 02:33 PM
#44
u235
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Originally Posted by AlmostTrick
So where do you stop? Part way up the hill is my guess. (allow yourself to coast until you're near stopped) Surely you wouldn't waste energy and brake at the bottom!
Yes, use the down hill after the peak and maybe you won't have to actually stop at all? Get in better shape so the hills are not a challenge
On MTB I won't use the down hill to recover. For one it's not a recovery at all and if I am exhausted the last thing I want to do is barrel down a rough trail. On the road it's not a big deal. Everyone is different.

Last edited by u235; 01-23-20 at 02:53 PM.
01-26-20, 05:25 PM
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Originally Posted by AllWeatherJeff
Maybe, maybe not. I'm trying to determine windchill factor not windspeed, per se. But I can guarantee that standing still in a 25mph wind versus traveling at 25mph into that headwind at 21°F are two entirely different experiences.

I may be mistaken, but what sounds implausible is that your response implies that at 21°F with a 25mph wind that a body will lose heat at the same rate whether standing still or in motion.
Your "body" isn't going to" lose heat" any faster due due to wind chill, regardless of wind speed or bicycle velocity, IF you cover your bare skin with appropriate clothing/outerwear while bicycling.
No doubt bicycle riding at 21°F while naked or with inadequate clothing covering bare skin is a very different experienceand merits paying real close attention to wind chill factors.
01-26-20, 05:33 PM
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Originally Posted by Notso_fastLane
One of the most notable items in your wardrobe that is conductive are you bike shoes.
An even more notable conductive item in some people's wardrobe that can be a doozy in very cold weather is pants with a
metal zipper fly. I learned that lesson when riding at -15°F while wearing jeans. Only made that mistake once. Metal eyeglass frames can also be a problem at very cold temps.
01-26-20, 06:43 PM
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Tip from an old NoDak’er- protect your crotch with some sort of wind block if it’s cold and your riding with any speed / wind. Ziplock bags work pretty well. And yes you vector add the wind speed / direction relative your speed / direction. You can be warm from exertion and still frostbite your upwind ear, fingers, toes, and the tip of your unit. If you ride to work at -30 with a 20 mph wind at your front you will learn these things.
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01-28-20, 02:22 PM
#48
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Originally Posted by AllWeatherJeff
If the temperature is 21°F and I'm cycling at 12mph into a 24mph headwind, is the windchill calculated using 36mph?

Similarly, if I'm traveling at 24mph with a 24mph tailwind is windchill negated?
I am a windchill-denier ... I don't believe in windchill.

First, if you put a glass of water out on a 35F day with 20 mph winds - the windchill is 11F, but that water will never freeze since the temp is still above freezing.

Windchill calculations are based bare skin ... I don't expect you're biking with bare skin when windchill is applicable (temps below 40F).

Lastly, what little bare skin you have (face) is typically warmed enough by the core to not suffer. Reference: this was a 90-minute ride at -28F (Jan 30, 2019 in Minneapolis) - goggles came off after 30 minutes because the fogged over. I was a comfortable with bare skin because my core was hot (this great training ride for my Arrowhead 135 goal)

01-28-20, 02:31 PM
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u235
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I am a windchill-denier ... I don't believe in windchill.

First, if you put a glass of water out on a 35F day with 20 mph winds - the windchill is 11F, but that water will never freeze since the temp is still above freezing.

Windchill calculations are based bare skin ... I don't expect you're biking with bare skin when windchill is applicable (temps below 40F).

Lastly, what little bare skin you have (face) is typically warmed enough by the core to not suffer. Reference: this was a 90-minute ride at -28F (Jan 30, 2019 in Minneapolis) - goggles came off after 30 minutes because the fogged over. I was a comfortable with bare skin because my core was hot (this great training ride for my Arrowhead 135 goal)
Wind chill is 100% a human factor and calculation. Splitting hairs but... If that water you put outside was 70F, it would reach 35 faster in that wind compared to no wind so there is a wind factor but that's not a wind chill calculation. That faster cooling rate is what your body feels with a wind. Insulate that cup and it cools down slower, same as you wearing a jacket. It is all related.

Last edited by u235; 01-28-20 at 02:53 PM.
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01-28-20, 02:37 PM
#50
AllWeatherJeff
Old Dog, New Tricks

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I am a windchill-denier ... I don't believe in windchill.

First, if you put a glass of water out on a 35F day with 20 mph winds - the windchill is 11F, but that water will never freeze since the temp is still above freezing.

Windchill calculations are based bare skin ... I don't expect you're biking with bare skin when windchill is applicable (temps below 40F).

Lastly, what little bare skin you have (face) is typically warmed enough by the core to not suffer. Reference: this was a 90-minute ride at -28F (Jan 30, 2019 in Minneapolis) - goggles came off after 30 minutes because the fogged over. I was a comfortable with bare skin because my core was hot (this great training ride for my Arrowhead 135 goal)

Ride 30 miles from home with a generous tailwind on a sub-freezing day. Then stop for 30 minutes to repair a rear flat tire. Now turn around and ride 30 miles home into the headwind. Now that your body has cooled down after the prolonged stop and the sweat trapped beneath your winter layers cools your body further still, you will very quickly become a believer in windchill.