One more excuse to skip riding when it's cold
#251
climber has-been
Thread Starter
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,238
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3540 Post(s)
Liked 3,695 Times
in
1,851 Posts
To avoid confusion, it might be better to speak of the partial pressure of O2. Which does increase with air density.
#252
Senior Member
Join Date: Jul 2008
Location: 25 miles northwest of Boston
Posts: 29,592
Bikes: Bottecchia Sprint, GT Timberline 29r, Marin Muirwoods 29er, Trek FX Alpha 7.0
Mentioned: 112 Post(s)
Tagged: 0 Thread(s)
Quoted: 5234 Post(s)
Liked 3,609 Times
in
2,357 Posts
why is it "fluid" dynamics, if one is talking about a gas?
#254
climber has-been
Thread Starter
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,238
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3540 Post(s)
Liked 3,695 Times
in
1,851 Posts
A gas and a liquid are both considered a “fluid”, because they both move and change shape in response to forces.
Likes For terrymorse:
#255
Tinker-er
Join Date: Oct 2007
Location: Mid-Atlantic
Posts: 481
Bikes: 1956 Rudge Sports; 1983 Univega Alpina Uno; 1981 Miyata 610; 1973 Raleigh Twenty; 1994 Breezer Lightning XTR; V4 Yuba Mundo aka "The Schlepper"; 1987 Raleigh "The Edge" Mountain Trials; 1952 R.O. Harrison "Madison"
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 177 Post(s)
Liked 291 Times
in
198 Posts
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.
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.
#256
Grupetto Bob
Join Date: Sep 2020
Location: Seattle-ish
Posts: 6,374
Bikes: Bikey McBike Face
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 2663 Post(s)
Liked 5,861 Times
in
3,017 Posts
#257
climber has-been
Thread Starter
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,238
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3540 Post(s)
Liked 3,695 Times
in
1,851 Posts
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.
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.
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.)
Last edited by terrymorse; 12-14-22 at 09:19 AM.
#258
Full Member
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.
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.
#261
Cheerfully low end
Join Date: Jun 2020
Posts: 1,980
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 646 Post(s)
Liked 1,051 Times
in
670 Posts
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
Otto
Likes For ofajen:
#262
Sock Puppet
Join Date: Oct 2022
Location: Planet Earth
Posts: 1,701
Bikes: 2014 Cannondale Synapse Carbon, 2017 Jamis Renegade Exploit and too many others to mention.
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 1031 Post(s)
Liked 863 Times
in
573 Posts
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%.
#265
climber has-been
Thread Starter
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,238
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3540 Post(s)
Liked 3,695 Times
in
1,851 Posts
density = PM/RT (ideal gas formula)
Likes For ofajen:
#267
climber has-been
Thread Starter
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,238
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3540 Post(s)
Liked 3,695 Times
in
1,851 Posts
And since dry air is more dense than moist air, there is slightly more wind resistance when absolute humidity is low.
Likes For DangerousDanR:
#269
Senior Member
Join Date: Jul 2008
Location: 25 miles northwest of Boston
Posts: 29,592
Bikes: Bottecchia Sprint, GT Timberline 29r, Marin Muirwoods 29er, Trek FX Alpha 7.0
Mentioned: 112 Post(s)
Tagged: 0 Thread(s)
Quoted: 5234 Post(s)
Liked 3,609 Times
in
2,357 Posts
#270
Senior Member
Join Date: Jul 2008
Location: 25 miles northwest of Boston
Posts: 29,592
Bikes: Bottecchia Sprint, GT Timberline 29r, Marin Muirwoods 29er, Trek FX Alpha 7.0
Mentioned: 112 Post(s)
Tagged: 0 Thread(s)
Quoted: 5234 Post(s)
Liked 3,609 Times
in
2,357 Posts
#271
Tragically Ignorant
Join Date: Jun 2018
Location: New England
Posts: 15,613
Bikes: Serotta Atlanta; 1994 Specialized Allez Pro; Giant OCR A1; SOMA Double Cross Disc; 2022 Allez Elite mit der SRAM
Mentioned: 62 Post(s)
Tagged: 0 Thread(s)
Quoted: 8186 Post(s)
Liked 9,099 Times
in
5,054 Posts
Likes For livedarklions:
#272
Tragically Ignorant
Join Date: Jun 2018
Location: New England
Posts: 15,613
Bikes: Serotta Atlanta; 1994 Specialized Allez Pro; Giant OCR A1; SOMA Double Cross Disc; 2022 Allez Elite mit der SRAM
Mentioned: 62 Post(s)
Tagged: 0 Thread(s)
Quoted: 8186 Post(s)
Liked 9,099 Times
in
5,054 Posts
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.)
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.)
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.
Likes For livedarklions:
#273
Senior Member
Join Date: Jan 2022
Location: Albuquerque NM USA
Posts: 520
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 233 Post(s)
Liked 323 Times
in
206 Posts
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.
I've had a scotch and I'm feeling a bit pedantic today.