Snapshot CdA's

[nn1]

I have recently upgraded to the iaero but still run a wired type mount with speedo sensor only. Have done my 20 coast downs and 4 mile ride and getting great results. But I cant get a snapshot CdA reading when coasting down hill with a 0 watts reading showing on the aero. Is this because there is no cadence signal?
I can see a wireless stem mount being ordered soon.
Neil (New Zealand)

[Site_Admin]

You do need a cadence sensor to get the Snapshot CdA.

[carstenj]

I am also having problems getting a Snapshot CdA. I use the Garmin heart rate strap and combined speed/cadence sensor and when I coast down a hill with the power window on the iAero I don't see a Snapshot CdA. I am not pedaling, cadence is 0, and I don't move for 20 seconds while going downhill.

Any idea about what I do wrong?

[coachboyd]

I am also having problems getting a Snapshot CdA. I use the Garmin heart rate strap and combined speed/cadence sensor and when I coast down a hill with the power window on the iAero I don't see a Snapshot CdA. I am not pedaling, cadence is 0, and I don't move for 20 seconds while going downhill.

Any idea about what I do wrong?

This might be a silly question, but in the setup screen do you have Cda turned on?

[Site_Admin]

Make sure you have cadence on your mount....

[carstenj]

@coachboyd: Yes I have turned Cda on in the setup screen.

@Whareagle: I am using cadence sensor and it is working just fine.

Any other ideas?

[iodaniell]

Any other ideas?

Two words (much speculation, of course)--circuit quiescence. Your iAero's circuit for detecting when to turn on the Snapshot CdA might be above threshold (noisy).

[carstenj]

I went into setup and turned the CdA feature on and off a couple of times and now it is working. Strange.

Next question

How should these snapshot CdA's be interpreted? In my profile I have a CdA of 0.393. When I did 3 snapshot CdA's today I got the following values: 0.51, 0.71, and 0.73. What are these value telling me?

[iodaniell]

I went into setup and turned the CdA feature on and off a couple of times and now it is working. Strange.

Next question

How should these snapshot CdA's be interpreted? In my profile I have a CdA of 0.393. When I did 3 snapshot CdA's today I got the following values: 0.51, 0.71, and 0.73. What are these value telling me?

The snapshots show that you were less aero than when you composed the profile currently loaded into your Aero.

The increase in CdA could occur because you were riding in a different position then when you did your CDs or have different clothing on (floppy jacket, arm warmers, leg/knee warmers, floppy pants, etc.) then when you did your CDs or you have different equipment mounted on the bike (fenders, lights, bags) then when you did your CDs.

Since, the numbers you provided are from one ride, then it could be assumed that you changed your position, such that 0.51 -may- be on the hoods and 0.71 and 0.73 -may- be on the tops and sitting more upright.

[andrep]

Fernando?!

I think about an upgrade to newton +. I am not so much interested in the powerstroke thing because I think that most the time in the relevant riding position (triathlon) my stroke and movements are not so bad. I had some tests in the past (ONLY Pressure measurement IN the shoes + DFPM on a trainer) and the results where not bad (but I had more power on the left than on the right side - round about 60/40 - so I am very interested if you one day will be able to measure the different feed or if you are working on it ... from my not sophistic point of view it should be possible for the Newton, to calculate differences in the power of the different legs ... but you are the experts. To much data? Or ... ? Some thoughts?

But beside this I am very interested in the upgrade because of the snapshot CDA? Please explain me how it is working? In the moment the cda is fix for my sice, weight and riding position (and still will be fix in the profile, I know) how is the snapshot working? What is my advantage of having it? will it help to dial in my profile more accurate because I know my cda in my riding position? What else is possible with it? Because I haven´t got another DFPM I can´t use the other functions and so you, Velocomp, has to tell me in your best words, why I should invest in the snapshot Cda By the way: Is the fathers day offer still available?!

[ronpei]

I too would like to know if the snapshot CdA requires a DFP device or does it work in stand alone on the Newton, as well I assume that the CdA is displayed in real time on the Newton while you coast?

[Velocomp]

I too would like to know if the snapshot CdA requires a DFP device or does it work in stand alone on the Newton, as well I assume that the CdA is displayed in real time on the Newton while you coast?

Snapshot CdA does not require a DFPM. Whenever you coast, CdA will appear on the screen after about 10 seconds of coasting.

[andrep]

Dear Velocomp,

would be nice, if you answer my questions above!

thank you!

[Russ]

andrep,

Since I have been tinkering with snapshot Cda since it was first released I will offer some observations that may help you.

On my typical rides, coasting downhill, I typically see a range of variability in my 'snapshot Cda' readings. That said, most of the hills on my ride vary in the roughness of the road surface, grade and at times curves.

In addition, to get usable data, your wind scaling value should be well dialed in (and zeroed, of course).
When the wind is variable or cars are passing, forget the data that is displayed.

So in simple terms, to make it most usable for position testing, a smooth straight hill, with conditions of zero wind make the feature the most usable. Taking several runs under those conditions at each position and averaging them may also be best, though I have not used it that rigorously, I think some have.

An oddball reason that I like it is that it gives me, over time, a feel for the way the iBike works as I begin to realize the contribution of riding on a surface that matches my Crr or one that is off a bit.

On a good day, I may see my Cda go from about .38/.39 to .44 or more on smooth to rough roads where my photographically measured and coastdown measured Cda is around .41 on the hoods. In this case I have my Crr set for +.1 over smooth roads. With winds I may see .32 or .50 or so pop in from time to time.

Also I was able to determine that my (now declared winter tires) Crr changed significantly with temperature by the offset occuring in my snapshot Cda readings. I can also use out of spec readings to find my wind zero or wind scaling may be off. The wind scaling does seem to be affected by large temperature differences, at least a bit.

On a day that I see my Cda display changing abnormally as my coasting speed increases, for a hill that I have come to know well, I may suspect my iBike settings (wind zero, windscaling or temperature affected Crr out of range). I also keep an eye on my relative wind to see if it changes much as speed increases - again only really meaningful if the wind is zero or if I keep seeing a pattern.

I think this is a somewhat ignored feature as using Cda with the DFPM makes for some much greater ease of collecting data and gets most of the attention in posts, from the sound of posts on that topic.

Hope this helps and I bet some will take issue with some of my observations. If I am wrong in some place perhaps better explanations may be offered!

Regards,
Russ

[KenS]

Also I've noticed with snapshot CdA that it seems to work best when you get up to a speed around 30km/h or more then slow down (not braking) or at least stop accelerating. The high speed is so that aero resistance swamps rolling resistance and I guess slowing down helps with the calculations. Of course this could just be my imagination.
Also, braking messes things up, so if I need to brake I backpedal first so Newton reads the cadence and turns of snapshot CdA. This is especially important if you want to analyse in Isaac afterwards.

[andrep]

Dear Russ and Ken - many thanks. you gave me some good arguments for purchase the upgrade!!!