5,284 reputation
11731
bio website
location
age
visits member for 3 years, 3 months
seen 2 hours ago

Jun
13
comment Is there a simple way to measure, record, and use wind resistance or tail winds?
Very nice. Two small correction: in part 2, air resistance varies with the square of air speed. Therefore, the power needed to overcome that air resistance approximately varies with the cube of speed (actually, (ground speed)*(air speed)^2 ). And, wind doesn't alway cancel out over the same route. Wind often has a pattern determined by geography and season, and wind speeds follow a Weibull distribution so, for example, you can end up with more extreme headwinds in the afternoon than tailwinds in the morning.
Jun
10
comment Is there a simple way to measure, record, and use wind resistance or tail winds?
Yes, the iBike (and other bicycle power meters) was discussed in this bicycles.stackexchange answer.
Jun
10
comment Is there a simple way to measure, record, and use wind resistance or tail winds?
Actually, we can measure all of those individual factors. However, measuring them all is either hard or expensive, and the OP's question was whether "there is a simple way" to do this. I was struggling with a way to write a simple response to a simple question but your short response is superior to the long (and growing) answer I was working on so I'm going to upvote yours and abort mine.
Jun
9
comment Is there a simple way to measure, record, and use wind resistance or tail winds?
There are, but they're of limited usefulness because you'd then need to "subtract" your ground speed from the indicated air speed to get the net speed of the wind. But since you're mostly interested in accounting for the wind speed in order to get a better sense of performance gains, there are other ways to measure that. I'll work on an answer.
Jun
8
comment Is there a simple way to measure, record, and use wind resistance or tail winds?
Is your question about measuring wind, or is it really about measuring performance improvements in the presence of wind that confounds the measurement? That is, there are anemometers that can measure and record wind but that's not particularly a bicycle-specific question.
Dec
24
comment How accurate are the power numbers from a Tacx Flow?
I'm not sure I understand your comment. The TACX documentation did not specify a particular value for calibration, so I just calibrated it so that it would be the same value (= zero) each time I used it. As I said, the Flow was consistent but inaccurate.
Dec
4
comment What bags will fit a Challenge Seiran SL?
Doesn't Challenge sell both a short rack and a Voyager rack that will fit the Seiran?
Nov
30
comment DIY computational fluid dynamics for aerodynamics?
Yeah, I guess I'm "that" guy. I think your question was a little open-ended but there's an interesting bicycle-related kernel in there. I'm thinking about how best to answer the kernel.
Nov
30
comment DIY computational fluid dynamics for aerodynamics?
Defraeye et al. (2010) did some work with CFD and wind tunnel measurements, and claimed to get reasonably good modeling. Getting quick CFD is the holy grail, of course -- but the problem is "quick."
Nov
29
comment DIY computational fluid dynamics for aerodynamics?
I don't know, I sorta like the reference to "the Chung Method."
Nov
15
comment Is the Power Pilot the only speedometer / computer that will work on a LeMond Revolution Trainer?
An alternative to buying a Power Pilot may be to mount a cheap speedometer using the small magnet attached to the "wheel", then use the information here to calculate power for speed, print that out on a sheet of paper, and tape it to the wall next to your trainer. If you can afford a slightly nicer ANT+ capable speed sensor plus ANT+ USB dongle, you can then use the trainerroad application or Golden Cheetah to display speed and power on a computer screen.
Nov
2
comment Terminology index - a list of bike part names and cycling concepts
@freiheit: It's an English word that is also a French word. That's like saying "Paris" is an English word that's commonly mistaken for a French word. In English, we pronounce "pannier" as "PAN-yer" and "Paris" as "PAIR-iss" but in French they are pronounced "Pan-YAY" and "Pa-REE."
Oct
31
comment Why choose a traditional frame over an aerodynamically streamlined frame?
Speed increased for the same power output. Power output decreased for the same speed. Power and speed were recorded electronically at one-second intervals. The electronic recording device was not influenced by the rider's beliefs, so claiming that the estimation of Crr and CdA was the result of a placebo effect is incorrect.
Oct
31
comment Why choose a traditional frame over an aerodynamically streamlined frame?
@meagar: Exactly. But the metrics are not speed and power. The metrics are CdA and Crr. We're using a power and speed recorder to record the data in order to calculate CdA and Crr, which are independent of speed and power. In fact, it's the variance in speed and power that make CdA and Crr estimable. We could have done the estimation with a powered electric bicycle, varying the throttle and speed and still estimated CdA and Crr. Even if the rider had a prior belief it's the relationship between power and speed that matters -- and that is what is recorded.
Oct
31
comment Why choose a traditional frame over an aerodynamically streamlined frame?
First, how could "a placebo effect" alter the recorded speed and power? Second, the field test was consistent with wind tunnel measurements. How could a placebo effect affect the wind tunnel? Third, I already pointed out that it was an example comparison of two frames that were already considered aero -- I used this example because the difference was smaller than usual. We really should move this to a discussion room if you wish to continue.
Oct
31
comment Why choose a traditional frame over an aerodynamically streamlined frame?
@DanielRHicks - we can (and probably should) move this to a discussion room if you wish but these advantages don't disappear. Here's an example of a field test under real-world conditions that measured the difference between two frames that were already pretty aero. Subsequently the rider raced in a 40K TT and his actual time came within half a second per km of the predicted time.
Oct
31
comment Why choose a traditional frame over an aerodynamically streamlined frame?
@DanielRHicks - You may have doubts but the differences have been measured in wind tunnels (with rotating front wheel) and also in field tests. Whether the difference is large enough to matter is a legitimate question; but whether the frames "provide measurable improvement" is not.
Oct
29
comment What road bike tire pressure is best for speed?
There is an example of rolling resistance on real roads increasing with increasing pressure about two-thirds of the way through this article.
Oct
16
comment Effective breathing for efficient cycling
Unlike weight-lifting or yoga, but like running and swimming, cycling is mostly about aerobic capacity. However, the efforts during cycling tend to be much more variable than running or swimming (especially running on a flat track or swimming in a pool). That means your respiration rate is going to be much more variable than in running or swimming (or weight-lifting or yoga). Sports which are more steady-state allow for more steady-state rhythm in breathing.
Oct
16
comment Velodrome atmospheric conditions
Oh, I was just commenting on your calculation of the power demand. At the speeds you were using in your example, rolling resistance will account for ~50 watts or so. OTOH, if you were just looking at differences in power demand with air density, it's easier to notice that an x% change in air density translates to exactly the same x% difference in aero drag.