Faster vs. Slower
#27
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From: Hill Country ;-)
While I wasn't thinking specifically about wind resistance when mentioning "efficiencies," you are correct that the faster speed will require more force. How much of your total power goes toward resisting the wind versus everything else (friction of the chain, the actual work required to move ___ lbs over a certain distance, etc.) would be interesting to know.
#28
While I wasn't thinking specifically about wind resistance when mentioning "efficiencies," you are correct that the faster speed will require more force. How much of your total power goes toward resisting the wind versus everything else (friction of the chain, the actual work required to move ___ lbs over a certain distance, etc.) would be interesting to know.
Wind resistance and rolling resistance (tires and drivetrain). Here's an example chart.
At 20 kph (12 mph), rolling and wind are each about half.
At 30 kph (19 mph), or 40 kph (25 mph) wind resistance goes way up compared to rolling resistance.
From the chart,
A 20 km ride at 20 kph is around 90 watts for an hour (add the two lines together.)
A 20 km ride at 40 kph is around 340 watts for a half hour.

At 20 kph (12 mph), rolling and wind are each about half.
At 30 kph (19 mph), or 40 kph (25 mph) wind resistance goes way up compared to rolling resistance.
From the chart,
A 20 km ride at 20 kph is around 90 watts for an hour (add the two lines together.)
A 20 km ride at 40 kph is around 340 watts for a half hour.

#29
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Over a fixed distance, riding harder will require more work and therefore burn more calories even though it will take you less time.
I have a flat route that I ride often. It's 10.8 miles. I compared a hard ride against a mellow one.
Hard ride: 27:21, 23.8mph, 295w, 484kj (https://www.strava.com/activities/57...ts/14048151684)
Mellow ride: 34:13, 18.4mph, 172w, 366kj (https://www.strava.com/activities/72...ts/17797804990)
There's a difference, but it's probably not as great as you might expect. The difference between an on-the-rivet TT effort and a smell-the-daisies recovery ride is 118 calories over almost 11 miles. That's like two Oreos. For 3.7 miles, it's going to be much smaller.
I have a flat route that I ride often. It's 10.8 miles. I compared a hard ride against a mellow one.
Hard ride: 27:21, 23.8mph, 295w, 484kj (https://www.strava.com/activities/57...ts/14048151684)
Mellow ride: 34:13, 18.4mph, 172w, 366kj (https://www.strava.com/activities/72...ts/17797804990)
There's a difference, but it's probably not as great as you might expect. The difference between an on-the-rivet TT effort and a smell-the-daisies recovery ride is 118 calories over almost 11 miles. That's like two Oreos. For 3.7 miles, it's going to be much smaller.
#30
Covering the same distance in less time on a bike burns more calories because you must overcome air resistance, which is proportional to your speed.
#31
#34
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Air resistance (drag) is proportional to the square of speed.
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
#35
#36
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From: Middletown NY
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Moving on a bike at a faster speed will burn more calories per minute but maybe not overall any more than at a slower speed. But there is something to be said about increased wind resistance effort and then, after the ride is over, your metabolism still stays elevated.
Even though it is a short ride, I would push myself to ride it as fast as I am capable of and log it on an app like Strava about once a week to chart my progress. Racing myself is a good motivator but yielding health benefits makes it that much better.
Even though it is a short ride, I would push myself to ride it as fast as I am capable of and log it on an app like Strava about once a week to chart my progress. Racing myself is a good motivator but yielding health benefits makes it that much better.
#37
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From: Albuquerque, NM
You can't seriously believe that air resistance pushes a rider ahead (negative resistance is propulsion).
You can't seriously believe that drag is proportional to e raised to the power of v squared (grows exponentially with velocity squared).
#38
Air resistance is proportional to

(sign is unnecessary here, you don't need the constant when saying "proportional", it's not exponential, and velocity in this question is the bike's ground speed)
#40
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Take your bike out in a gale that would knock you off your feet. Turn it downwind and enjoy a free ride at 30+ mph.
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
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#41
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#42
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#43
if we're getting geeky and picky here:
Air resistance is proportional tothe negative half of the drag coefficient, cross sectional area, and air density, and grows exponentially with in proportion to velocity the apparent wind speed squared.

(sign is unnecessary here, you don't need the constant when saying "proportional", it's not exponential, and velocity in this question is the bike's ground speed)
Air resistance is proportional to

(sign is unnecessary here, you don't need the constant when saying "proportional", it's not exponential, and velocity in this question is the bike's ground speed)
Last edited by jfowler85; 11-08-16 at 01:13 AM.
#44
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Drag = 1/2 roe V^2 S Cd where roe = the mass density of air, V= velocity, S = Area (wing area for this treatise), Cd = coefficient of drag
Drag (sir resistance) grows with velocity squared and is proportional to area, air density and coefficient of drag, ie the drag characteristics of that shape.
I'm just a dumb engineer trained in fluid mechanics. I have never heard of the 'negative half of" anything, nor that air resistance grows exponentially with velocity. Maybe I was asleep (for six years) or perhaps my professors were not the best. Granted, the reference I gave, although once considered the bible on wing sections and the reference from which many airplanes were designed (and flew), was published in 1949 and probably quite wrong by now.
Ben
#45
From "Theory of Wing Sections" by Abbot and von Doenhoff:
Drag = 1/2 roe V^2 S Cd where roe = the mass density of air, V= velocity, S = Area (wing area for this treatise), Cd = coefficient of drag
Drag (sir resistance) grows with velocity squared and is proportional to area, air density and coefficient of drag, ie the drag characteristics of that shape.
I'm just a dumb engineer trained in fluid mechanics. I have never heard of the 'negative half of" anything, nor that air resistance grows exponentially with velocity. Maybe I was asleep (for six years) or perhaps my professors were not the best. Granted, the reference I gave, although once considered the bible on wing sections and the reference from which many airplanes were designed (and flew), was published in 1949 and probably quite wrong by now.
Ben
Drag = 1/2 roe V^2 S Cd where roe = the mass density of air, V= velocity, S = Area (wing area for this treatise), Cd = coefficient of drag
Drag (sir resistance) grows with velocity squared and is proportional to area, air density and coefficient of drag, ie the drag characteristics of that shape.
I'm just a dumb engineer trained in fluid mechanics. I have never heard of the 'negative half of" anything, nor that air resistance grows exponentially with velocity. Maybe I was asleep (for six years) or perhaps my professors were not the best. Granted, the reference I gave, although once considered the bible on wing sections and the reference from which many airplanes were designed (and flew), was published in 1949 and probably quite wrong by now.
Ben
To say that air resistance grows exponentially with velocity is just another way to say that it is proportional to the square of velocity - which we can say because the exponent in question is on an identified variable - and is more a reference to the graphed function rather than the equation itself. The plots in a graph of the axes velocity and resistance do not rise in a linear fashion, they rise with an exponential slope.
It's a convoluted derivation which is simplified for the sake of rough estimation, as I posted above. The point here is to nit-pick the nit-picker by complicating the formulation for the sake of being a dick, though ironically those who responded to this have instead simplified the formula to a more basic estimation of air drag. Makes me chuckle.
Last edited by jfowler85; 11-08-16 at 02:18 AM.
#46
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From: Albuquerque, NM
#47
Okay let's do some basic algebra. Draw a graph with velocity and air resistance each on a respective axis - it doesn't even matter which goes where. Now plot some arbitrary points using the air resistance formula.
It should look something like this:
https://www.everythingmaths.co.za/sci...fffb562e27.png
Get it yet? My guess is that you did not read and/or understand the whole of the comment to which you are replying. Try a re-read.
#48
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From: Vancouver, BC
Okay let's do some basic algebra. Draw a graph with velocity and air resistance each on a respective axis - it doesn't even matter which goes where. Now plot some arbitrary points using the air resistance formula.
It should look something like this:
https://www.everythingmaths.co.za/sci...fffb562e27.png
Get it yet? My guess is that you did not read and/or understand the whole of the comment to which you are replying. Try a re-read.
It should look something like this:
https://www.everythingmaths.co.za/sci...fffb562e27.png
Get it yet? My guess is that you did not read and/or understand the whole of the comment to which you are replying. Try a re-read.
#49
It should look something like this:
https://www.everythingmaths.co.za/sci...fffb562e27.png
Get it yet?
https://www.everythingmaths.co.za/sci...fffb562e27.png
Get it yet?
#50
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Joined: Apr 2006
Posts: 4,609
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From: Albuquerque, NM
I love when I get to write that (probably too much).






