Puzzling results
Posted: Mon Apr 15, 2019 6:06 am
I'm still having a hard time getting results that make sense when I do CdA testing.
Yesterday I did some comparisons between two bicycles, my road bike with clip-on aerobars and my tt bike. The road bike has shallow road rims (Velocity A23 rims, Industry 9 hubs) and the TT bike has aero wheels (Zipp 404 front, 808 back).
I used the same TT helmet and wore the a skin suit for all of the tests.
The course is an out-and-back.
The weather report at the beginning showed wind speed of about 6-7 mph and it did not feel gusty though I'm not sure the wind speed was correct; I don't have a way to measure that independently. It felt like the wind increased gradually during testing, again I don't have a way to measure.
The bikes both use C1 chainring DFPMs that appear to correlate well when compared against a 3rd DFPM (either P1 pedals or my trainer; I strongly prefer Speedplay pedals but the P1s have their uses).
Immediately prior to each of the activity files I have attached I did a full calibration ride on the same road, though the calibration ride included a longer section of the road so the final continuous riding portion could be done without braking or turning around. Immediately prior to the calibration ride I re-set the zero offset of the DFPMs.
The CdA estimates were obtained by selecting the relevant lap and using the average HR reported by Isaac.
The road bike activity files are limited to data from the actual test.
The TT bike activity file has 5 laps, laps 1,3 and 5 are the CdA tests. Lap 3 differs from all the other test laps in that I wore a jersey over my skin suit to see if I could measure the difference.
Other than the change of bikes and the use of the jersey everything under my control was exactly the same.
The results do not make sense to me:
Road with Clip-on
0.294
TT bike (lap 1, no jersey)
0.277
TT (lap 3, with jersey over skin suit)
0.264
TT (lap 5, no jersey)
0.270
Road with Clip-on
0.209
On the TT bike I did lap 5 as a measure of the stability of the estimates from Laps 1 and 3. On the road bike the second CdA measurement was used for that same purpose.
I know from extensive experience that I am significantly faster on the TT bike than on the road bike even when I use the clip-on aerobars on the road bike so the 5th test (repeat test of the road bike) makes no sense at all and the difference between the two road bike measurements is huge.
It's hard to imagine that wearing a jersey makes me more aero.
Is there an obvious problem with either the ride files or the protocol?
Yesterday I did some comparisons between two bicycles, my road bike with clip-on aerobars and my tt bike. The road bike has shallow road rims (Velocity A23 rims, Industry 9 hubs) and the TT bike has aero wheels (Zipp 404 front, 808 back).
I used the same TT helmet and wore the a skin suit for all of the tests.
The course is an out-and-back.
The weather report at the beginning showed wind speed of about 6-7 mph and it did not feel gusty though I'm not sure the wind speed was correct; I don't have a way to measure that independently. It felt like the wind increased gradually during testing, again I don't have a way to measure.
The bikes both use C1 chainring DFPMs that appear to correlate well when compared against a 3rd DFPM (either P1 pedals or my trainer; I strongly prefer Speedplay pedals but the P1s have their uses).
Immediately prior to each of the activity files I have attached I did a full calibration ride on the same road, though the calibration ride included a longer section of the road so the final continuous riding portion could be done without braking or turning around. Immediately prior to the calibration ride I re-set the zero offset of the DFPMs.
The CdA estimates were obtained by selecting the relevant lap and using the average HR reported by Isaac.
The road bike activity files are limited to data from the actual test.
The TT bike activity file has 5 laps, laps 1,3 and 5 are the CdA tests. Lap 3 differs from all the other test laps in that I wore a jersey over my skin suit to see if I could measure the difference.
Other than the change of bikes and the use of the jersey everything under my control was exactly the same.
The results do not make sense to me:
Road with Clip-on
0.294
TT bike (lap 1, no jersey)
0.277
TT (lap 3, with jersey over skin suit)
0.264
TT (lap 5, no jersey)
0.270
Road with Clip-on
0.209
On the TT bike I did lap 5 as a measure of the stability of the estimates from Laps 1 and 3. On the road bike the second CdA measurement was used for that same purpose.
I know from extensive experience that I am significantly faster on the TT bike than on the road bike even when I use the clip-on aerobars on the road bike so the 5th test (repeat test of the road bike) makes no sense at all and the difference between the two road bike measurements is huge.
It's hard to imagine that wearing a jersey makes me more aero.
Is there an obvious problem with either the ride files or the protocol?