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Forum: "The 33"-Road Bike Racing

02-27-14, 09:46 AM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

GPS's determine speed by the change in location...

GPS's determine speed by the change in location over time. They have the time piece right but they can be off by a couple of meters in location. That's not much but if you're trying to measure speed...

Forum: "The 33"-Road Bike Racing

02-27-14, 08:35 AM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

Sorry to take so long to respond. Real world life...

Sorry to take so long to respond. Real world life interruptions.

You've read the the .pdf (http://anonymous.coward.free.fr/wattage/cda/indirect-cda.pdf), right? Slide 70 discusses integrating the...

Forum: "The 33"-Road Bike Racing

02-25-14, 08:07 PM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

The simplest way is to convert from a...

The simplest way is to convert from a speed-and-power equation to a work-and-distance equation that solves for a CdA for a given Crr, and vice versa. If you have two runs taken at different initial...

Forum: "The 33"-Road Bike Racing

09-15-13, 11:51 AM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

Very nice. With those data I got slightly better...

Very nice. With those data I got slightly better fit with Crr=.0061 and CdA=.389 (but I probably make very slightly different assumptions about the course). In any event, for an actual test I would...

Forum: "The 33"-Road Bike Racing

10-22-11, 07:56 PM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

That's about it. In this example I did only two...

That's about it. In this example I did only two runs because I was only trying to show that it could be done, and done with pretty minimal equipment. I'd do at least one more in a real attempt, then...

Forum: "The 33"-Road Bike Racing

10-21-11, 08:43 PM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

Yeah, I wasn't suggesting turning your legs over...

Yeah, I wasn't suggesting turning your legs over because of a "windmilling" effect -- I was suggesting it for exactly the reason you were pointing out: I have difficulty remembering to get my legs in...

Forum: "The 33"-Road Bike Racing

10-21-11, 07:17 PM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

Well, as I said, there was a tiny amount of wind...

Well, as I said, there was a tiny amount of wind that we assumed away. The real reason not to simply solve the work conservation equation and stop is because we only had two equations for two...

Forum: "The 33"-Road Bike Racing

10-21-11, 07:09 PM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

Yeah, maybe 0.1% is a tad optimistic -- but...

Yeah, maybe 0.1% is a tad optimistic -- but there's something wrong with your dv/dt. I'm guessing you were just using a simple difference? Real roads don't change slopes as drastically as you're...

Forum: "The 33"-Road Bike Racing

10-21-11, 04:20 PM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

Ah, we must be calculating the dv/dt slightly...

Ah, we must be calculating the dv/dt slightly differently. Here are my slopes:

223965

Forum: "The 33"-Road Bike Racing

10-21-11, 03:19 PM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

Oh, I don't know 'bout that. 223948

Oh, I don't know 'bout that.
223948

Forum: "The 33"-Road Bike Racing

10-21-11, 03:15 PM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

So, here's the main point: if you have a way to...

So, here's the main point: if you have a way to record second-by-second speed (and more riders are buying devices that can do this every day) then you can do coastdowns that will let you estimate...

Forum: "The 33"-Road Bike Racing

10-21-11, 02:18 PM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

How about a hot dog cuz, ladies and germs, we got...

How about a hot dog cuz, ladies and germs, we got a WEINER. You can get max slope by plugging the Crr and CdA back into the power equation and solving for the slope. Overall average slope is -1.8%,...

Forum: "The 33"-Road Bike Racing

10-21-11, 01:22 PM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

Hmmm. I'd like to see me at 67 kg, too. I'd also...

Hmmm. I'd like to see me at 67 kg, too. I'd also like to see me younger, taller, better-looking, and flanked by nubile young women. Oh, wait. I've already got that last bit covered.

Let's not...

Forum: "The 33"-Road Bike Racing

10-21-11, 11:02 AM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

Ah, you're definitely on the right track. Here's...

Ah, you're definitely on the right track. Here's a hint: integrate the power equation over time to convert it into a work equation.

Exactly.

Not quite. That's close to true for the max...

Forum: "The 33"-Road Bike Racing

10-21-11, 09:52 AM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

Fair enough. I'm usually too lazy to do it that...

Fair enough. I'm usually too lazy to do it that way, too: pure coastdowns are more hassle than being able to do (powered) loops.

However, if you did solve the challenge, one of the important...

Forum: "The 33"-Road Bike Racing

10-21-11, 07:05 AM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

That's an acceptable method. I don't expect them...

That's an acceptable method. I don't expect them to do square roots or logarithms with paper and pencil, so using Aerolab is fine. The main point is that if you have a way to record speed you can do...

Forum: "The 33"-Road Bike Racing

10-21-11, 06:34 AM

Replies: 44

You know, it's possible to estimate CdA and Crr without a power meter

Views: 7,454

Posted By RChung

You know, it's possible to estimate CdA and Crr without a power meter

Y'all probably know that it's possible to estimate CdA and Crr with field tests using a power meter. It's also possible to do it without a power meter -- it's more hassle but it's still possible.
...

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