terrymorse 

To avoid confusion, it might be better to speak of the partial pressure of O2. Which does increase with air density.

rumrunn6

planes fly higher to gain benefits from "thinner" air
why is it "fluid" dynamics, if one is talking about a gas?

spelger

liquid, gas...all the same

terrymorse 

A gas and a liquid are both considered a “fluid”, because they both move and change shape in response to forces.

PhilFo 

Don't move the goal posts. This is solely about air density.
Yes, wind is a thing and drag from it is definitely a force that cyclists must overcome. Wind is not air density. That said, the difference in density (in a standard atmosphere, with the same amount of water vapor) between 0C and 35C is not a factor because the difference is so very slight. Any difference in performance is due to other confounding factors.
But keep on, keeping on. You do you.

rsbob 

terrymorse 

There is definitely some density on display here <eye roll>.

One more time: Wind drag is the dominant force to overcome in cycling, wind drag is a linear function of air density, and air density varies with the reciprocal of (absolute) temperature.

A drop in temperature from 35C to 0C *increases* air density and thus wind drag by about 11%. That is a significant increase to the dominant force in cycling!

That’s as simple an explanation as I can think of. Hope that it makes sense this time.

(BTW, about “me doing me” — Thermal Sciences were my specialty, academically and professionally.)

cjenrick

Cooler air does slow you down. Anybody who has done their fare share of riding knows this by actual experience. I average about 1 mph less in the winter. Part of this is the extra clothing and lack of motivation to pedal hard in harsh weather along slippery surfaces. And then there is the reduced tire pressure and soggy leaves and wet pavement to add to the mix.

If you have ever bombed down a long decent and hit a patch of cooler air you will notice a dv/dt.

And of course the humidity is a lot higher in the winter time.

But these are just my viewpoints, put forth to help you with your holiday depression.

ofajen

I think air density should vary as 1/T, correct? It will look fairly close to linear over such a relatively small span of absolute temperature.

Otto

DangerousDanR

For some of us the absolute humidity is much lower in the winter.

ofajen

I think it would be sobering to see the rolling resistance of a tire as a function of temperature. Lower temperature has a significant effect on the properties of rubber materials. My instinct is that rolling resistance changes more than air resistance for the tires I run and for my relatively low winter MUP speeds.

Otto

Lombard

Correct. The dew point is obviously much lower in the winter than in summer - otherwise we would be in a perpetual state of frozen precipitation.

Relative humidity isn't a whole lot different in cooler vs. warmer weather, but in a heated building where the dew point doesn't change a whole lot from outdoors, relative humidity drops drastically hence the feeling of the air being very dry in winter. We speak of "hot and humid" weather when it's 90 and the dew point is 70. However, when it's 70 and the dew point is 50, it's a comfortable day. In both of these cases, the relative humidity is 50%.

Flip Flop Rider

so what's the verdict..ok to ride in the cold?

Lombard

If we had an official verdict, this thread might end. We can't have that.

terrymorse 

You’re right, thanks for catching that.

density = PM/RT (ideal gas formula)

ofajen

I hope it’s not… that way I can feel naughty when I do. 😊

Otto

terrymorse 

Probably true in most places.

And since dry air is more dense than moist air, there is slightly more wind resistance when absolute humidity is low.

DangerousDanR

Also when there is a 30 MPH North Wind howling down from Manitoba 🥶

rumrunn6

I prefer Absolut condensation

rumrunn6

go for it. you won't be alone

livedarklions

OK for most people, not ok for those it's not ok.

Any "controversy" here was created by distorting the point of the OP.

livedarklions

To me the issue is that if I ride here (NH) in the winter, the road conditions are so generally bad that I won't be able to achieve speeds where I'd notice that 11%.

I think this whole discussion of air density started with a claim that you get some kind of fitness bonus riding in the denser air. This is really just the "heavier bike means better workout" fallacy yet again. Your effort is your effort regardless of marginal differences in resistance. All increasing the density of the air does is mandate that you'll be going slower for the same effort.

Mtracer

As someone else mentioned, liquids and gases are in fact both fluids. But liquids and gases are not the same thing. Air at standard conditions is a gas (like the air we breathe), while at standard conditions, water is a liquid (like what we drink).

I've had a scotch and I'm feeling a bit pedantic today.

spelger

i was being nonchalant with my response. consider mine to be a summary of the OP's response.

prj71

moist.