viewtopic.php?f=2&t=205
and therefore borrowed this late-1990s Campy Shamal front wheel from my friend Jim Martin to test using my usual approach:
Letting the intercept "float", the results were:
Zipp 808:
CdA = 0.241 +/- 0.003 m^2
Crr = 0.00345 +/- 0.00029
Campy Shamal:
CdA = 0.240 +/- 0.003 m^2
Crr = 0.00365 +/- 0.00067
So, seemingly a very slight edge to the Shamal. However, both wheels were fitted with new Bontrager Aerowing TT tires that were purchased at the same time and weighed within a couple of grams of each other, both were inflated to the same pressure immediately before testing using the same pump, and the tests were done back-to-back on the same day under essentially constant environmental conditions. One could therefore argue that fixing the intercept using the average of the two sets of experiments would be a better approach - if you do that, the picture reverses:
Zipp 808:
CdA = 0.240 +/- 0.003 m^2
Crr = (fixed at 0.00355)
Campy Shamal:
CdA = 0.241 +/- 0.003 m^2
Crr = (fixed at 0.00355)
Thus, my overall conclusion is that it is basically a wash, at least when both wheels are fitted with narrow, aerodynamically-designed tires and tests are performed at/near 0 deg of yaw. It is quite possible, however, that a significant difference would exist under other conditions (with the 808 presumably out-performing the Shamal).
As for why my results seemingly differ from Alex's (who in some comparisons found the Shamal to be faster than an 808 or a front disk, but in other tests found it to be slower), I do not know. It could be due to differences in the way the tests were performed (e.g., higher average yaw angle on the track), or it could be due to the fact that Alex's wheels were fitted with very similar, but not identical, used tubulars, which could have varied in either their rolling resistance or their aerodynamic properties.
(BTW, to make certain that I was really comparing apples-to-apples, for each of the runs I calculated the development of the fixed gear that I used based on the gear ratio, my cadence, and my speed as measured at the front wheel - on average, the difference between the two sets of experiments was only 0.1%, i.e., the circumferences of the two front wheels were apparently within 0.1% of each other. Nonetheless, I corrected for this trivial difference anyway.)
