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...

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...

Good info real useful to bicycle commuters :rolleyes:
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.

Congratulations, you completely missed the point of my post. :rolleyes:

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.

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.

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.

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.