2ND CDA

[racerfern]

I'm getting comfortable enough with the current iBike setup that I'm ready to tackle the 2nd CDA adjustment. The problem is that with the current software I'm seeing a lot of "NaN" where I would want to change the numbers. I can't seem to get it working. Ideas and suggestions are welcome.

[Site_Admin]

Just. Hang. On. It's doable, but it's largely a WIP.

[travispape]

I'm getting comfortable enough with the current iBike setup that I'm ready to tackle the 2nd CDA adjustment. The problem is that with the current software I'm seeing a lot of "NaN" where I would want to change the numbers. I can't seem to get it working. Ideas and suggestions are welcome.

Where are you seeing the NaNs? Maybe a screenshot would help.

[racerfern]

Where are you seeing the NaNs? Maybe a screenshot would help.

As soon as I get home this evening, I'll post it. From memory it's in the advanced screen of 2nd CDA, I think.

[racerfern]

Here is the screen shot with the NaN. Under detailed analysis, I click on Add Second CdA...

2NDcda.jpg (79.24 KiB) Viewed 11532 times

And if I click the up or down arrows at the 2nd CdA (m^2), then I also get NaN just above for the 2nd CdA Factor.

[travispape]

And if I click the up or down arrows at the 2nd CdA (m^2)

I'm not sure how you would have gotten an NaN, but fave you tried typing in a number instead of just using the arrows? Try typing ".4".

Travis

[racerfern]

OK. Here's the deal. I can add a 2nd CdA if I open the original downloaded file. I keep all my original downloaded files in one directory. Then I do the weather, analyze the tilt, etc and save to a separate location. If I ever mess up a file for whatever reason, I can just load the original download and start over.

When opening the file that has already been analyzed I get NaN, when opening the original, I can make the 2nd CdA adjustments along with using all the other analysis features.

Now, I thought that using the 2nd CdA was to allow for being in a more "tucked" or aerodynamic position at higher speeds. Therefore the power output at those speeds should go down in relation to the original info. That is not happening. If I up it to .4 the power and change the cutover speed to 22, the power goes up. What am I doing wrong?

[travispape]

OK. Here's the deal. I can add a 2nd CdA if I open the original downloaded file. I keep all my original downloaded files in one directory. Then I do the weather, analyze the tilt, etc and save to a separate location. If I ever mess up a file for whatever reason, I can just load the original download and start over.

When opening the file that has already been analyzed I get NaN, when opening the original, I can make the 2nd CdA adjustments along with using all the other analysis features.

Could you send me one of your analyzed files that gives you an NaN? Just in case, export the profile that belongs to it also.

Now, I thought that using the 2nd CdA was to allow for being in a more "tucked" or aerodynamic position at higher speeds. Therefore the power output at those speeds should go down in relation to the original info. That is not happening. If I up it to .4 the power and change the cutover speed to 22, the power goes up. What am I doing wrong?

Actually, the 2nd CdA is for the opposite case. The assumption is that you have done your coastdowns & 4 mile ride in your aero position (e.g., in the drops or with bent elbows) and that you use your aero position most of the time. The 2nd CdA is for introducing a less aero position that you use at lower speeds below the cut-over speed (e.g. straight arms on the hoods or on the tops). So if you do introduce a 2nd CdA, the power should only go up.

Travis

[racerfern]

@ travis: Check your email.

Also, I understand about the 2nd CdA. So I should look to make CdA changes climbing hills.

I did my Cds and 4 mile ride in my most common riding position elbows slighly bent, hands right behind the brake hoods. Now when I go down to the drops on some higher speed flat or slightly downhill runs I was looking to make a CdA adjustment for that part.

Thanks,

EDIT:
So the Cutover Speed should really say Cutunder Speed?

[scittkit]

Okay, I get the 2nd CDA. Is there a big enough power difference between riding in the drops and the hoods to concern myself with? I rotate between the two constantly and it would be a nightmare trying to figure that out.

[racerfern]

Actually, the 2nd CdA is for when sitting upright and being less aero not more. Thanks Travis for straightening me out on this. So the question is when huffing and puffing up a significant length hill how much extra effort am I making because I'm sitting straight up.

I guess I should do a set of CDs and a four mile ride sitting straight up just so I know what my CdA is in that position.

It will be sweet when you can highlight a section of your ride and apply a 2nd CdA to that section. I'll keep my eye out for v2.1.

[Isaias]

Actually, the 2nd CdA is for when sitting upright and being less aero not more. Thanks Travis for straightening me out on this. So the question is when huffing and puffing up a significant length hill how much extra effort am I making because I'm sitting straight up.

I guess I should do a set of CDs and a four mile ride sitting straight up just so I know what my CdA is in that position.

It will be sweet when you can highlight a section of your ride and apply a 2nd CdA to that section. I'll keep my eye out for v2.1.

Wouldn't a hill be way to the other end of the spectrum (i.e., air resistance is not the big factor, gravity is)? I'd think that the 2nd CdA would be more appropropriate in conditions where air resistance is a big factor (like on flats or descents), but your position is less aero than the 1st CdA.

[travispape]

Wouldn't a hill be way to the other end of the spectrum (i.e., air resistance is not the big factor, gravity is)? I'd think that the 2nd CdA would be more appropropriate in conditions where air resistance is a big factor (like on flats or descents), but your position is less aero than the 1st CdA.

It is definitely true that when climbing, aero resistance is a smaller factor than gravity; however, the idea with this feature is that the rider would use their best aero position for most of their riding since aero resistance is by far the largest source of loss for most road riding conditions. You want to do your coastdowns in the ride position that you mostly use. The purpose of the 2nd CdA feature is to get a better measurement of your power if you take a more comfortable position at lower speeds. Even though aero is a smaller factor at the slower speeds, it is nice not to be penalized in your power tally for taking the more comfortable position for climbs.

I can see that some riders could tuck into and even better aero position than their primary position for high-speed decents and it might be useful to introduce a 3rd CdA feature; however, it would only be useful if you actually pedal during those decents. If you don't pedal, power will record as zero no matter what aero position you take. (Of course, you'll get better coasting speed if you tuck, but power is always zero for coasting.)

Also, there's the argument that if you have a better pedaling tuck position, why not use it all the time when you are working against the wind?

Anyway, I'll make a note of the idea. In the mean time, think of 1st CdA as your aero-efficient position for working against the wind--the position you would usually use--and think of 2nd CdA as your comfortable position for climbing and tailwind scenarios. For the best overall accuracy, you would want to do your coast-downs in the fast position that you employ in the majority of your riding when your primary foe is wind.

Travis

[racerfern]

I can see that some riders could tuck into and even better aero position than their primary position for high-speed decents and it might be useful to introduce a 3rd CdA feature; however, it would only be useful if you actually pedal during those decents. If you don't pedal, power will record as zero no matter what aero position you take. (Of course, you'll get better coasting speed if you tuck, but power is always zero for coasting.)

Also, there's the argument that if you have a better pedaling tuck position, why not use it all the time when you are working against the wind?

I do have a better tuck position for sure but not for producing power. I find myself hunkering down and pedaling hard in slight downhill -.5% to -3% or long flat tailwind runs in a group. These are relatively high speed. It's a tradeoff for me. I definitely produce less power in the drops (10% less maybe even less than that??) but save on aero. When I am in the drops the change of using different muscles to do most of the work takes its toll on the legs. At least that's how I feel it happening.