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Commuting Bicycle commuting is easier than you think, before you know it, you'll be hooked. Learn the tips, hints, equipment, safety requirements for safely riding your bike to work.

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Old 04-10-14, 09:11 AM   #51
e0richt
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When I would wear a backpack, I found that the straps would start to stress my chest / pecs causing me to be more tired than riding without it. But this was a general backpack... probably the higher end ones are more aero and I would hope that they would have a chest strap to alleviate strain...
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Old 04-10-14, 11:38 AM   #52
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Originally Posted by wphamilton View Post
I hadn't seen this until someone revived the thread, but if you're still reading the total mass was the same for all tests.
I think droy45 was just talking about the comfort factor of weight on the torso (adding to pressure at the butt/seat interface) vs weight on the bike. But perhaps you meant to respond to Aravilar, who was asking about mass and speed...
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Old 04-10-14, 12:00 PM   #53
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Good info real useful to bicycle commuters
Obviously filling the large backpack with greased bowling balls will allow a speed obsessed commuter to shave a few micro seconds off the commute, especially if the commute is on the face of the moon.
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Old 04-11-14, 09:08 PM   #54
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Originally Posted by Aravilar View Post
Earth's atmosphere is not a vacuum. Conceptually, the gravitational force scales linearly with mass (since gravitational acceleration is constant, for this anyway) but the air resistance (drag) does not.

Longer explanation is here: https://sites.google.com/a/mpstraini...nlighterriders
Congratulations, you completely missed the point of my post.
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Old 04-14-14, 03:16 PM   #55
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Congratulations, you completely missed the point of my post.
All I read was some useless exposition on a scenario completely unrelated to cycling. I just made sure other people wouldn't be confused by it.
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Old 04-14-14, 03:23 PM   #56
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I think droy45 was just talking about the comfort factor of weight on the torso (adding to pressure at the butt/seat interface) vs weight on the bike. But perhaps you meant to respond to Aravilar, who was asking about mass and speed...
Precisely so, I must have clicked on the wrong post to quote.

I'm just letting the side conversation run, although I will say that weight matters on the coast-down due to higher density objects having a higher terminal velocity. And more momentum per drag area when the slope levels off. Not sure where a vacuum enters into it.
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Old 04-16-14, 03:22 PM   #57
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Precisely so, I must have clicked on the wrong post to quote.

I'm just letting the side conversation run, although I will say that weight matters on the coast-down due to higher density objects having a higher terminal velocity. And more momentum per drag area when the slope levels off. Not sure where a vacuum enters into it.
Thanks for doing this experiment. Do you mind uploading or sending me the source data?

That said, are you serious? There is no air in a vacuum, hence there is no drag. If there is no drag, terminal velocity is only limited by how far you have to fall until you reach relativistic speeds.
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Old 04-16-14, 03:42 PM   #58
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Thanks for doing this experiment. Do you mind uploading or sending me the source data?

That said, are you serious? There is no air in a vacuum, hence there is no drag. If there is no drag, terminal velocity is only limited by how far you have to fall until you reach relativistic speeds.
If I can dig it up I could just post it here.

Re vacuum, it's not very pertinent to coasting down a hill or biking to work. That's sufficiently handled with rho in the drag equations, which you utilize for terminal velocity. I think for our purposes we can consider the air density to be constant during a ride, and even disregard the actual value entirely if you're just looking for a ratio of drag coefficients (it divides out).
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Old 04-16-14, 03:45 PM   #59
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If I can dig it up I could just post it here.

Re vacuum, it's not very pertinent to coasting down a hill or biking to work. That's sufficiently handled with rho in the drag equations, which you utilize for terminal velocity. I think for our purposes we can consider the air density to be constant during a ride, and even disregard the actual value entirely if you're just looking for a ratio of drag coefficients (it divides out).
Thanks!

We're talking about two different things; for your experiment, the drag coefficient is essentially constant. I was speaking re: vacuum regarding the other conversation about falling in atmosphere and falling in vacuum.
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Old 04-16-14, 05:12 PM   #60
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Good experiment, especially given the budget...

If you had a barometer and a thermometer you'd have enough info to solve P=rho*R*T but over the course of your test series it seems unlikely to change much and not enough overall to change the conclusions for different weather.

If you are interested in a condition where drag doesn't matter - one of my longtime online aquaintances was a judge recently at the NASA rover challenge where high school teams build folding 4-wheel offroad HPV's and ride them around Redstone. I can't think of any way that streamlining would help those guys.

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