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j.shanney wrote:
Looking over my garmin data it was around 26MPH as recorded by a magnetless garmin speed sensor.

Is that what the 6W figure relates to, or is it normalized to the 200W given in the chart?
rruff wrote:
j.shanney wrote:
Looking over my garmin data it was around 26MPH as recorded by a magnetless garmin speed sensor.

Is that what the 6W figure relates to, or is it normalized to the 200W given in the chart?

My guess is it is normalized to 200W so we have a common point for comparison but you would have to ask Jim since im not an expert on all the formulas involved.

The speed data his calculations use were from a different speed sensor mounted on my chainstay that used a magnet on the rear wheel. I think he said the magnetless one wasn't accurate enough. So his speed data may be slightly different than mine.
Quote:
Maybe you've learned to have a more intuitive sense of CdA, but I think you'd be in the minority there. We spend all day looking at power meters. Except Jim, and a few others. I do my own Chung testing, but even then I like to look at Watt differential at the speeds I'm going.

Right now, I would say the easiest way to get a sense of CdA is try out BestBikeSplit. You'll quickly get a sense of what a change of 0.007 means for you and your chosen course.

Case in point.
• local monthly TT course (hilly 24km out and back)
• reduce my calibrated CdA by 0.007
• hold everything else constant
BBS' prediction suggests I would save 15 seconds. That seems to agree well with the ERO Sports article.
Given the amount of time that I have spent in the wind tunnel testing athletes and my experience with Jim at ERO, perhaps I do understand it a bit more. It would do well for you to take the time to understand it also. Most of the watt savings stated are based off the ROT that goes .005CdA~=.5sec/km~=5watts. This is at the typically tested tunnel speed of 48kph.

A .005 reduction to CdA at 48kph is almost 7 watts, But it takes a rider ~400 watts to go that speed with a starting CdA of .25. A rider capable of pushing 200 watts is going to be looking at a savings of a bit less than 3 watts.

As others have said when someone says something saves X you have to look at the specific conditions and speeds in which they were tested. CdA completely eliminates the guess work as it is a relative constant and scale pretty linearly.

trail wrote:
Ex-cyclist wrote:
CdA doesn't change appreciably with speeds that cyclists ride. Watts on the other hand can vary quite a bit.

There are CdA figures, near the bottom. Though I find Watts more useful.

Yeah, I get it. But at least for me differential Watts are a more accessible mechanism for understanding the magnitude of effect.

If he had just reported the CdA differences of 0.006 (which is roughly what it was), I'd have to spend some time converting that to something else.

Reporting that it saved 6W @ 200W is immediately accessible.

Maybe you've learned to have a more intuitive sense of CdA, but I think you'd be in the minority there. We spend all day looking at power meters. Except Jim, and a few others. I do my own Chung testing, but even then I like to look at Watt differential at the speeds I'm going.[/quote]

Heath Dotson

Seems like a big delta. My garage wind tunnel work moons ago suggests a smaller difference between brakes:

Garage Wind Tunnel Data!

in order to get 3W at 30mph with my setup, I had to do this:

Furthermore, I noticed the phrasing of "transparency" in the tri rig article linked above. A long time ago, a simkins brake was tested using the same field testing approach and the raw power meter data files were published. That was a nice touch by Matt.

cheers,

=================
Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
=================
The Omega is on sale right now from Tririg. I just ordered one for my IA16. I have the Vision Trimax that I got from someone who upgraded an IA10. Now it's time for me to really upgrade.

---------------------------
''Sweeney - you can both crush your AG *and* cruise in dead last!! ðŸ˜‚ '' Murphy's Law
I'll try to get all the Excel files up online if I get a chance; doubt I'll have time before Rio. Next test I post, I'll make the files available for download, though that, too, will be after Rio.

These articles have to be consumable to the average athlete, not those who like to pour over all the data, which I respect, but most people would stop reading real quick if I put all the data in the article itself.

As for the CdA's, well, I have to swallow my pride and admit I was the third test rider and, at 6'2", 240lbs, my CdA is a bit embarrassing. We're actually going to have some fun with that and keep recording my drag numbers both on the velodrome and in the tunnel as I lose about 50-60lbs. That will be a fun article...How Weight Really Matters! My next test will be in about 3 weeks and down about 20lbs.

Jim Manton / ERO Sports

Aero Tidbits posted on Instagram & Facebook
Jim, just have to say that I really enjoy your postings......but my bank account doesn't. I just had to buy myself a brake after reading the data. Early birthday present I guess.
Would be very interested to see how the Magura caliper compares (with and without the fairing).
Nick B wrote:
As much as I like ERO and Tririg (owned an omega brake and tested with ERO), these time savings seem too large.

Agreed:

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