Aero/power testing results
I posted a while back that my power drops from an FTP of about 235 sitting up to 200 or so in the aero position. To confirm that I'm faster in aero at 200 than at 235 sitting up, I did some aero/power testing based on the Chung method. You can read the details on the Wattage Google Group, but the basic jist is to do multiple laps of a course with some elevation variation without touching the brakes on a windless day. You then import the power file into a spreadsheet, estimate rolling resistance (typically .004 to .006 depending on tires and road conditions), and manually adjust CdA or aerodynamic coefficient until the hills and valleys of the loop elevation are all at the same height when seen on a graph in the spreadsheet. It's really not all that complicated, and very effective. I tried it using various rolling resistances, each of which come up with a different CdA, but the relative differences are all about the same.
The bottom line is that sitting up my CdA is .363 with a CRR of .005. In aero position, my CdA goes to .288 with the same CRR. The resulting speeds are that at 200 watts, my speed in aero on flat ground is 22.1 mph given the weather conditions that day (warm and humid), and 21.8 at 235 watts sitting up. So I go .3 mph faster while using 35 fewer watts. Given that the speeds are about a wash (4 min. difference over 112 miles) , hopefully the lower power will translate into more energy for the run. One more data point: given my positions, 195 watts in aero = same speed as 235 watts sitting up.
These tests were done without aero wheels and a regular helmet. One of these days, I may test the advantage of putting the deep wheel in front and the cover on the back to see real world how much it helps.
Comments
This type of testing is on my long list of things I want to do someday but haven't made time to do.
Mike
No "hopefully" about it. This is the whole point of the EN race exeuction strategy. You could estimate your TSS for 112 miles for an NP of 165 aero (and IF of 0.7 for your FTP of 235) vs 198 (sitting up), and then look at the "Legs Bank Account" table to see just how wasted you'd be. But don't bother. You wouldn't even finish 56 miles at 198 watts sitting up and be able to run 13.1 miles.
Vince
For those that have poked at the Chung method in the past and had their eyes roll back in their head (not that I'd know anything about that), check this out:
I haven't tried Aerolab yet, but will give it a try.
The regular Chung method isn't too hard. The most important thing is to find a good course. Anywhere from .5 miles to a 1.5 miles is good, and try for four or more laps. It must be a windless day, and you cannot touch the brakes at all. Don't change position at all either. Coasting is OK. (I had one 90-degree left turn that I had to coast before.) You also need some altitude variation. The course I did had about 35 feet of up and down per mile, which was plenty. Hit lap at the start and again at the end of all the laps together so you can find the section easily, or just note the approximate times. If you're having trouble with the spreadsheet, you can send me the power csv file and I can play with it.
I tried another method last fall that consisted of multiple passes at different speeds on a perfectly flat course. That method is capable of resolving both CdA and crr. Unfortunately, after an hour or two of testing without gloves on a 40 degree morning, my Garmin 310XT destroyed the power file, so I don't have the results. That was on my road bike.