Jump to the table at the end, and you’ll see that in runs 9-12 they compared a Sub 9 against a 900 mounted in a P3C (as shown in the pics) and with a rider aboard at both 10 and 20 deg of yaw. What isn’t clear to me (and perhaps someone who has been to the A2 wind tunnel can chime in) is whether or not the data have been corrected for the (minor) differences between runs in wind tunnel speed (and hence dynamic pressure, q). Assuming that they have, however, the Sub 9 appears to have ~20 g less drag at 10 deg of yaw, but ~20 g more drag at 20 deg of yaw. As such, these results appear consistent with Zipp’s claims re. the magnitude of the potential time savings with a “bulged” disk vs. a flat disk (i.e., ~20 less grams of drag at 10 deg of yaw = a savings of ~10 s in a 40 km TT).
What is the data in the far right (under the red headers) represent? I couldn’t figure out why it was done at 40 mph, that doesn’t look like straight scaling of data from the ~29.5 mph data so I didn’t quite understand.
Assuming that they have, however, the Sub 9 appears to have ~20 g less drag at 10 deg of yaw, but ~20 g more drag at 20 deg of yaw.
well, considering the variance between runs one and two w/the 404/sub-9 combo @ 20 degrees, I’m not even sure about that one. I think the test rider must have ‘pulled a Tom’ and raised his head or something…
A 37 gram difference between two runs, while trying to get resolution on a 20 gram difference? I’ll let Robert tells how many runs we’d need to make the results statistically significant, but I’m guessing it’s more than ‘two’…
I think this speaks to the difficulty of testing wheels with a pedaling riders as much as anything else (which, in principle I think is a really good idea). That said, I’ll use this as evidence anyway to show that I was right about a bulged disc in a P3C, and use it as my ‘told you so’ moment. Thanks!
The ‘808/sub-9’ data seems conspicuously absent, as well? Who the hell TT’s with a box-section 404, anyway??
Assuming that they have, however, the Sub 9 appears to have ~20 g less drag at 10 deg of yaw, but ~20 g more drag at 20 deg of yaw.
well, considering the variance between runs
Apparently you were absent that day in class when we discussed the true meaning of the word “appears” to a scientist.
Assuming that they have, however, the Sub 9 appears to have ~20 g less drag at 10 deg of yaw, but ~20 g more drag at 20 deg of yaw.
well, considering the variance between runs
Apparently you were absent that day in class when we discussed the true meaning of the word “appears” to a scientist.
I think I blew it off to attend a logic class (or was it stats??). Regardless, it ‘appears’ to me that 'testing wheels with a pedaling rider is tricky business…
Jump to the table at the end, and you’ll see that in runs 9-12 they compared a Sub 9 against a 900 mounted in a P3C (as shown in the pics) and with a rider aboard at both 10 and 20 deg of yaw. What isn’t clear to me (and perhaps someone who has been to the A2 wind tunnel can chime in) is whether or not the data have been corrected for the (minor) differences between runs in wind tunnel speed (and hence dynamic pressure, q). Assuming that they have, however, the Sub 9 appears to have ~20 g less drag at 10 deg of yaw, but ~20 g more drag at 20 deg of yaw. As such, these results appear consistent with Zipp’s claims re. the magnitude of the potential time savings with a “bulged” disk vs. a flat disk (i.e., ~20 less grams of drag at 10 deg of yaw = a savings of ~10 s in a 40 km TT).
Hmmmm^TM…when comparing the CdAs of the 2 setups at 10 degrees, it looks like they’re identical (@ 2.007 ft^2)…and at 20 degrees, the 900 setup has a lower CdA than the Sub9 setup (1.734 vs. 1.760 ft^2)…and I agree that the “variation” between the 2 Sub 9 runs is sorta high…although neither run is as low as the 900 setup.
Now you can see why I think CdAs should be compared when looking at wind tunnel data, NOT “grams of drag” or whatnot…I’d also be curious to know why A2 insists on using ft^2 instead of m^2 for the area measurement?
As such, I think these results are MORE consistent with Mr. Vroomen’s claims that with a well shaped seat tube, a “shaped disc” doesn’t get you much…
Hmmmm^TM…when comparing the CdAs of the 2 setups at 10 degrees, it looks like they’re identical (@ 2.007 ft^2)
Indeed, they are - in my late-Friday-afternoon haste I only looked at the drag data; the odd units of the CdA results caused me to overlook them. I’m also used to looking at data from the TAMU tunnel, where the drag data are normalized for difference in q.
In the case of a disk wheel, there are few, if any
conditions where a front disk wheel
outperforms a low drag, low spoke-count
wheel, and there are few if any conditions
where a rear spoked wheel outperforms a disk
wheel. Front disk wheels maintain popularity
in indoor track events which is mostly a carryover
from technology decades ago when low
spoke count; aerodynamic rims could not
outperform disk wheels. However, dozens of
low spoke-count wheels are available that
outperform even the lowest drag disk wheels.
Other than for the Kirin event, there is no
reason to use a front disk wheel.
Do you think the GB track cycling team forgot to test this and just went with tradition!?!
Now you can see why I think CdAs should be compared when looking at wind tunnel data, NOT “grams of drag” or whatnot…I’d also be curious to know why A2 insists on using ft^2 instead of m^2 for the area measurement?
As such, I think these results are MORE consistent with Mr. Vroomen’s claims that with a well shaped seat tube, a “shaped disc” doesn’t get you much…
Maybe because they are located in NASCAR country?
Pay for shaped seat tube = save money on flat disc.
“AC is an arrogant ass” - Paulo Sousa 03/20/09
Why thank you! Coming from the original smartasscoach, that’s quite a compliment. Unfortunately, I can’t add it to my .sig file as I’m already at the five line limit. Maybe if you come up with something a little more original?
Assuming that they have, however, the Sub 9 appears to have ~20 g less drag at 10 deg of yaw, but ~20 g more drag at 20 deg of yaw.
well, considering the variance between runs
Apparently you were absent that day in class when we discussed the true meaning of the word “appears” to a scientist.
I think I blew it off to attend a logic class (or was it stats??).
Well it must not have been stats, or if it was then you have forgotten that neither alpha nor beta should be considered written in stone, but instead chosen based on the context of how the results will be applied.
