For me, it does not feel the same because I put my body in different positions depending on wind direction. I open my position up for max comfort and oxygen downwind and sacrifice both going upwind. So, yes, upwind is harder. Do you guys go upwind with the same big wind target? And if yes, why?

Sorry, by “crank inertia” I really meant “crank inertial load”, which combines all the effects of rider/bike mass and inertia along with gear ratio. The rotational inertia of the crank itself is trivial.

This study of crank inertial load may be relevant here. In particular the HL and HH conditions (low vs high inertial load when riding on flat ground). HL would be equivalent to a headwind and HH a tailwind.

https://rcnl.rice.edu/PDFs/jb2002.pdf

Key points are:-

1. There will be a lower crank inertial load when riding into a headwind at the same power.

2. Lower crank inertial load is associated with riders freely choosing a lower cadence.

I also think in reality that few riders actually do ride at the same power into a headwind. Most riders naturally increase their power like when going into a climb. In a tailwind it is very tempting to soft pedal occasionally, even when riding hard. A headwind is far more relentless, again like a climb.

And the applicable velocity is the airspeed, not the ground speed.

For a ground speed of 20 mph and a wind of 10 mph:

Into wind: air speed 30 mph
With wind: air speed 10 mph

Relative power required for aerodynamic drag; factor of 27.

The word perceived is the key here. It does not feel the same, no, mainly because you're battling against an element. At least, not for the average joe. Different conditions means different perceived efforts. 300w at 30kph against a headwind does not feel the same as 300w at 40kph with a tailwind. One is fun, the other isn't. This is when and why mental resilience is key in endurance sport. The magic happens between your ears.

I'm going to say a headwind is similar to Zwift/indoor training or climbing. Along with all of the fun physics stuff listed above - its the lack of "micro" breaks you get when riding with a tailwind. A headwind is constant steady resistance, always forcing you to keep momentum, forcing you to keep steady power on the pedals.

I often find it easier to maintain steady state power into a headwind (or on a climb) than I do with a tailwind.

My main route, a path along a canal that connects two large bays (Chesapeake and Delaware bays) is a funnel for wind. It's either a headwind or tailwind if the wind is coming from all but due North. Every other wind get's funneled down the canal. Winds out of the South cause a tailwind/headwind/tailwind/headwind situation - as the winds come up the bays and meet at the midpoint of the canal.

What's fairly interesting, no matter the wind direction or speed - at a constant power level, my ride times are within a few min of each other over the 30 mile out and back.

Yep. Wind at the back is similar to a flywheel effect, making pedaling feel less choppy. Ondrej Sosenka set a "human-powered" (drop bars, no aero anything) hour record in 2005 on a bike that was equipped with very heavy wheels for exactly that reason.

I even notice this effect on Zwift. At a high simulated road speed when the trainer flywheel is really motoring I find that the perceived effort at say 250W is lower than when climbing at 250W at a much lower flywheel speed. My trainer also has a motorised virtual flywheel to simulate descents. Again this makes perceived effort feel lower.

Again this is all about how crank inertial load varies with speed and gearing.

Yes, that's why asking riders what their cadence is or, worse, advising other riders what their cadence should be, is mostly misguided. Cadence varies with power, crank inertial load, fatigue, and volitional intent. Cadence is a red herring.

interesting. i find it much harder to sustain a certain amount of power either into a headwind or going uphill. tailwind feels like 15% more power for the same RPE. i have always suspected inertia more than cooling but physics was too long ago.

the math says it takes around 3x the power to sustain 15mph in a 15mph headwind, which makes sense given the other less exponential variables. at studlier speeds, say 20mph, and more typical winds, like 5mph, it’s 40% more.

Right. It's like the difference between climbing at threshold for half an hour vs trying to do threshold on the flats for half an hour. Same power but it FEELS totally different. I find it WAY easier to motivate myself to do the climb than to try that on the flat.

I think some riders are more sensitive to differences in crank inertial load than others, just like some riders are more sensitive to hotter/cooler conditions than others. I think I tend toward better power modulation under low CIL than high.

I liked the idea of doing TTs but I kinda suck at it. Most TTs are relatively flat and are done under high CIL conditions and I had a lot of trouble modulating power: I'd either undershoot or overshoot my power target. It's much easier for me to modulate power on a climb (though I have that watts/kg thing going against me, so there's that). Basically, I'm a perceptual dullard.

Their theory on why cadence naturally increases with high CILis quite interesting.

My local roads are constantly undulating with very few long flat sections. Trying to hold constant power or cadence or constant anything is pointless and slow anyway on these roads. My only steady state efforts are on the indoor trainer, but other than long alpine climbs I prefer riding undulating Zwift courses too. I find flat roads very boring when riding solo. In a fast group they can be fun though!

Are you, perhaps of a brawny physique? I'm thin, so I guess I have a high surface area to mass ratio. Winds affect me fairly heavily. My friend is a similarly strong rider. I have the edge at climbing. I asked him about headwinds, and he responded as if he hadn't heard of them. He's heard of them, but he doesn't really notice them. I think if you're bulky, you have a lower surface area to mass (or surface area to power) ratio.

I remember once, riding with woman who was probably 110lbs soaking wet - about half my weight at the time. We were swapping pulls and we had just reached the top of a mile-plus descent of around 1-2%. She figured it was her turn, so she took the lead and tried to pull, pedaling like mad with me behind her constantly braking to keep from rolling over her. I told her, "Here, let me" and just pulled the rest of the way down the descent. I knew the basic physics, but seeing her struggling to reach 20 mph on a road where I could coast up to 25+ was revealing. I weighed twice as much, but didn't have twice her frontal area.

freaking gravity!!!!

Not to mention aerodynamics.

Recently ran across two rides I did days apart that tell the story of wind. First one 200km down the Florida Keys to Key West, completed in 7 hours including stops, with a significant tailwind start to finish. Back north a few days later into the wind, 10 hours. I do not have power data, but my recollection is I rode hard on the downwind leg just because it was so frickin' fun. I worked hard on the headwind leg because I had no choice.

The difference was 3 more hours of perceived misery than hours of perceived joy.

No, it's not gravity. Heavy things fall at the same rate as light things. It's the aerodynamic drag that makes a difference.

No, it is gravity. In the scenario above, she would have had less drag than him. The benefit he got from being behind is a big factor of course (especially at only 1-2%) but heavy things definitely do not fall at the same rate as light things.

Not until you reach terminal velocity and that would be higher for her.

edit: I am not posting before 5AM again. Of course mass isn’t the cause of a heavier rider rolling downhill faster (doh!), but the lower drag force relative to the graviational force as per the comment above about not being twice the frontal area.

uh, the force exerted on the object is proportional to its mass, which is why the relationship of force to drag is changed and heavy objects roll downhill faster.

Do you actually own a power meter?

Ime, ppl rider harder into the wind to maintain speed, just like they ride harder up hill. Thats why they "think" hills and headwind is hard. They are not compensating enough, ie. not slowing down enough. If you own both, try pairing a power meter and a HR monitor and Im betting your HR is the same no matter if you do 150w at 12 mph into the wind, 150w in a tail wind at 24 mph or 150w up a hill, as long as you maintain the same cadence. One watt is one watt, no matter what you do.

The gravitational force is proportional to mass, but so is the force required to acheive a certain acceleration so they cancel out and all other things being equal (primarily aero or mechanical drag) then all objects will fall or roll down hill at the same speed. Of course, all other things are not equal.

It depends how you look at it.

If both riders had the same mass then any difference in speed would be due entirely to differences in aerodynamic drag and rolling resistance.

But if one rider was significantly heavier they would roll faster even despite a potential increase in aero drag. Mass is the dominant factor in the equation. Changes in mass affect rolling speed in a cubic function, while aerodynamic drag affects speed in a square function.

So really it is mass which makes fatter riders roll faster on descents unless they have a parachute on the bike!

yes, and the force which acts/depends on mass is gravity, so the root cause of moving downhill at all is gravity! that was my initial and subsequent point, despite being well aware that the rate of acceleration from gravity is not dependent on mass. i remember that much physics

with dramatically reduced gravity but similar aerodynamic friction (say inside a habitat on the moon), the result would be different.