First Attempt at Aero Field Test- Need help Estimating Crr

Triathlon Forum
1

After months of waiting for a day without snow or strong winds I attempted my first aero field test this morning.

The weather was perfect except for the temperature, zero wind but only 38 degrees. I read something by rruff that says to adjust Crr by .8%/F. The surface was a paved rail trail, I would call it smooth, but not perfect. On a 1 - 10 scale I would rate it a 7 or 8 for smoothness.

I was running GP4000S with latex tubes. If the temp was hot I would use something like .004-.0042 for Crr. If I am understanding rruff’s correction factor, I would use about .0056 at 38 degrees? This makes a pretty significant difference to the computed CdA.

If it matters here is the rest of the weather data:
38 degrees F
30.09 in barametric pressure
35.2 Dew Point
87% humidity
calm

I did 10 runs of an out and back course, five each way, at varying speeds. I have run the info through several different spreadsheets to determine CdA, but the assumed Crr has a large impact.

Anyone have any input?

Thanks

2

Thanks Tom.

I ran the numbers through rruff’s spreadsheet using your figure of .0042 for Crr. For the 10 runs CdA ranged from a low of .178 to a high of .224 with an average of .209. Some of the variance may be due to the fact that there were a few people walking on the trail during some of the runs which resulting in looking up more often. These were the runs with the higher CdA.

I guess this highlights the importance of head position.