Post files and let's have a look.

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AndyF
bike geek

AndyF wrote:

Post files and let's have a look.

Awesome, thanks! Let me know if this link works:

http://tpks.ws/6dZv

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Alex Arman

Strava

For a quick view and analysis:




Lap 3: Flat arms
Lap 5: Half Mantis
Lap 7: Full Mantis

I feel like I added drag going half mantis but then dropped drag overall going full mantis position.


Thanks in advance for anyone's input.

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Alex Arman

Strava

How do I pull down the ride file?

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AndyF
bike geek

I thought there may be a way to extract from Training Peaks. My bad.

Here is the .fit file in DropBox: https://www.dropbox.com/...01-07-00-58.fit?dl=0

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Alex Arman

Strava

Ok, next step is to figure out what the air density was at the time your were testing. Can you please find:
1) barometric pressure (at your altitude)
2) temperature
3) relative humidity
?

And then what your equipment was. Tires and tire pressure, wheels.

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AndyF
bike geek

There is big dip in speed on lap 5 and 7. Any idea what that is ?


Correction : there are some zeros (errors) in the data that are causing it

1) 29.95
2) 60 degrees F
3) 74% Dew Point 53F


Wheels were Williams 22s, basically. http://www.williamscycling.com/...l-System-22_p_7.html I used the same rims and hand built them.
Butyl tubes with Hutchinson Equinox 23c tires - about 85psi. Just my training setup.


This is an actual pic from that day, in full praying mantis mode.

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Alex Arman

Strava

Not a big deal, but how much do you weigh ?

At 78kg (bike+you) I see parrallell and half mantis very similar.2756/.2786ish, and praying mantis about .015 better at .2623

I used an Rho of 1.2174 and a crr of .004. At higher CRR I still see the full mantis better, but of course the cda numbers are different.

I had to correct those two dropouts in the data

Hope I was close. Andy is the goto guy!

Thanks! So .015 improvement, thereabouts, going to full praying mantis. We're talking about 10-15watts savings??

(Pink)Who wants to help fund a wind tunnel trip for validation?!?(Pink)

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Alex Arman

Strava

Ok, so I went to this page and found the air density to be:
1.2176 kg/m^3


Next up, your mass (bike included)?

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AndyF
bike geek

Might I ask, how did you set up the bars in full mantis? just rotate the base bar? or something else?

Yeah, I just rotated them up using my 3T clip ons. Some bars that do not have extension tilt in them, you can just mount a ski bend extension in backwards.

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Alex Arman

Strava

I would say about 78kg. I'm 67kg, plus shoes, Giro Selector helmet, and the bike above.

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Alex Arman

Strava

Wow, I'm so sorry this is so late, doublea334. I was at the PanAm Games and totally forgot.

The results are as follows (see this set of screenshots for details):

Lap | CdA (m^2)
3a | 0.2715
3b | 0.2788
5a | 0.2722
5b | 0.2809
7a | 0.2572
7b | 0.2699

Any idea why the start of the laps are always lower? If there's wind, then you'll want to several laps per setup to average things out. I would use 4 full laps with each setup. I know that can take a while, but it's better to get a small amount of good data than a whole bunch of bad data.

It seems to confirm that a full mantis works well for you. This is true for most people. Typically, the issue is the ability of a bike positioning coach to get you comfortable with that setup.


Hope this helps!

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AndyF
bike geek

So the deltas are 0.0073, 0.0087, and 0.0127... call it 0.0075 to make things easy so he saves ~7.5watts full mantis? Right?

That sounds right. Full mantis: it's a thing, now. ;-)

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AndyF
bike geek

Thanks!!

Maybe I sat up a bit at the end of each lap? Not sure. It was on a small .5mi neighborhood circle. 6 or so laps each run.

I tried to adapt to mantis position mid season but really struggled. So ultimately came back to level arms.

If ot saves me that 10ish watts, then I will certainly make it a priority to adapt this winter!


Thanks for all the help!!

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Alex Arman

Strava

This is just a thought, but maybe you need a good bike fitter? We make software and hardware that measures aero drag very well. But that's just the "what" of the aero question. The "how" is a different story altogether. I never aero position someone without consulting a top-notch bike positioning coach. I have a bag of aero tricks, but how to make them work for someone is the realm of professional bike fit.

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AndyF
bike geek