Advice interpreting ride data

[Guido_K]

Hello,
I spent today with my first try to get some CdA data for different setups. I got a few equipment item around and would like to figure out which combination is best for me on my bike. I got my road helmet, my Spiuk long tailed TT helmet, a Xlab Torpedo bottle, and a Torhans Aero 30 vertical bottle.

My plan for today was to set one reference point, I chose my road helmet and no bottle attached and did a calibration ride in this configuration.

This morning following the guidelines I chose long testing intervals of 15km each. After 3 rides I paused to have a look at the data and to be fair, I could not make anything from it.

In the late afternoon into the sunset (how temperature sensitive is this kind of testing?) I chose shorter intervals of about 1.5km but did 4 per configuration.

From the ride file I read the following:
Road helmet, no bottle: 0.241
Road helmet, Torpedo bottle: 0.238
TT helmet, Torpedo bottle: 0.233
Road helmet, Torhans bottle: 0.197
TT helmet, Torhans bottle: 0.214

The CdA for the first 3 configurations seems to be reasonable. While in aerodynamic terms not stellar I am very happy that I got such reasonable data. The final two seem to be off. However, what bothers me is that there seems to be a lot of variation between runs with the same setup.

I got basically three questions. Am I reading the ride file correctly, how do I figure out what went wrong at the end of my testing, and do you advice how to improve my approach?

Thank you very much for any advice,

Guido

[Velocomp]

Sorry for the delay in responding; I am traveling.

It looks like the ride file you attached is from your PM ride; is this correct?

You have lap markers in your ride file; are these for the 5 different configurations?

I don't see the "4 intervals per configuration". Where are they in your ride file?

It looks like you're using the "Tools/CdA Analysis..." function; is that correct? There is nothing wrong with that but note that Isaac recalculates CdA data in this window. I prefer to use the actual CdA data from AeroPod, available in the HR window. Take average HR, multiply by 4 then divide by 1000.

Here is the CdA data I get from your HR information:

Road helmet, no bottle: .208
Road helmet, Torpedo bottle: 0.208
TT helmet, Torpedo bottle: 0.204
Road helmet, Torhans bottle: 0.204
TT helmet, Torhans bottle: 0.198

In general, I trust AP/HR data more, because the CdA measurement methods in AeroPod come from real-time sensor data. The recalculations in Isaac use different, and "older" calculation methods.

There are two comments on your route:

1) You have a hill in the ride. You'll see that CdA data varies a bit in the humps. This is normal, but for maximum consistency I would avoid test routes with bumps/hills

2) At km 27 there is an abrupt reduction in CdA. My suspicion is that AP was bumped/rotated out of its position. Make sure you AP is securely attached.

The equipment changes you are trying to measure are pretty small. Your data looks good to me.

[Guido_K]

Thank you and no worries! Yes, I used the Tools/CdA analysis. I will revisit my ride file and check the position of my aeropod.

I am very sorry for the confusion, the interval markers are set by Isaac. I tried to change them but failed so far. I need to get deeper into the software yet.

One more question regarding the route. I read that you have no general objections against using multiple repetitions of smaller intervals. How long should they be? Would about 1km enough? That would cut out the hill and eliminate that problem. And would doing more repeats per configuration help.

Yes, the equipment changes are not big. But in a way, that is where the fun starts since every manufacturer claims their product makes one faster.

Thank you again,

Guido

[Velocomp]

1KM should be long enough, particularly if you are doing multiple repetitions . More data is better!

When you use the lap feature on your Garmin a lap marker is placed in the ride file.