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Zipp Aero Data- finally- comparing data with rider
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I couldn't find this posted or discussed- but very interesting aero data- comparing various zipp wheels- on an aero fram P3, with rider, and actual savings gained versus nebulous "save x time by using this wheel"

http://www.zipp.com/...pAeroEdgeFlyer_2.pdf

For example- zipp- says the 1080 is 8 seconds faster than an 808- when used in rear position- in the above chart.


When they talk about their wheels in the product section- they say the 1080 is 16 seconds faster than the 808 (the seconds are nebulous and nicely doubled- but they aren't real world- i.e. rider and bike)
http://www.zipp.com/...?SortField=ISBN,ISBN

When you start looking at the numbers- the top rider chart seems inflated- (and of course- their stand alone data- has always been inflated) if we use data on zipp's webite- such as
http://www.zipp.com/.../ZippCatalog2007.pdf on page 36...

Zipp - Home of the 2 and-a-half times rounder bearing 1 watt = 2-3 seconds over 40 K. The difference between career defining


victory and just another finish. Which explains why cyclist and triathletes are so obsessed with watts.


So- let's give Zipp the benefit of the doubt on their numbers and be in the middle where 1 watt = 2.5 seconds. So when you compare the 808 versus 1080- with the top chart- they are saying a difference of 33 to 35 watts- or 2 watt difference- is actually 1.5 seconds x 2 watts = 3 seconds- not the 16 seconds listed above in the wheel data section (as that's 8.0 seconds/watt), nor the 10 seconds (as that's 5.0 seconds/watt) listed with their rider/Cancellera chart. And ALL their numbers in the Cancellera chart uses 1 watt = to 3 seconds or more... in a sense inflating the savings of every single wheel- over the base wheel. They make a fine product- but man- can't they at least be consistent? Or give a range- 24 watts saving = 48 to 72 seconds... not just the 72 seconds.
Last edited by: mlinenb: Apr 2, 08 19:27
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Re: Zipp Aero Data- finally- comparing data with rider [mlinenb] [ In reply to ]
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 I do belive that Zipp wheels are excellent , and one of the best if not the best nut thios data are inconsistent and show the marketing manage that try to raise the bar of his numbers
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Re: Zipp Aero Data- finally- comparing data with rider [mlinenb] [ In reply to ]
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The problem is that bearings don't experience yaw angles. A bearing is always, always, always going to save 1 watt.

Wheels, on the other hand, DO see yaw angle. So the time savings shown are a reflection of normalizing with some metric over a range of yaw angles. The 1080 is going to be much faster than the 808 at higher yaw angles, and not much faster at all at lower yaw angles.

And it is industry standard to test wheels in a standalone environment, because it is much more repeatable. So testing a wheel solo gives a much cleaner picture. It often does give different numbers than testing wheels on a bike, but then again, you can't test every wheel, on every bike, with every rider.

You are attacking Zipp for being open and honest that not all wind tunnel sessions say the same thing because not every windtunnel session uses the same protocol (wheel only, wheel + bike, wheel + bike + rider).

Zipp is not trying to pull the wool over anyone's eyes. It's not their math that doesn't add up. It's your understanding of how windtunnel tests are conducted.

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp
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Re: Zipp Aero Data- finally- comparing data with rider [Rappstar] [ In reply to ]
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Rappstar- first- maybe disclose that you are sponsored by zipp....? then... check out the following.

okay- just look at the pdf... the rider data- and tell me what the seconds per watts, equal?

14->16 W = 2 W = 6 sec = 3 sec / watt
16->20 W = 4 W = 14 sec = 3.5 sec/wat
20->21 W = 1 W = 2 seconds = 2 Sec/Watt <---- maybe about right
21->24 W = 3 W = 8 sec = 2.66 sec/watt
24 ->26 W = 2 W = 8 sec = 4 sec/watt
26 ->27W = 1 W = 2 sec = 2 sec/watt
27->30 W = 3 W = 8 sec = 2.66 sec/watt
30 ->33 W = 3 W = 8 sec = 2.66 sec/watt
33 -> 35 W = 2 W = 10 sec = 5 sec/ watt <---- hyper inflated

The PDF makes no sense, since the seconds per watts are not uniform.
Unless I'm missing something -- I'm not saying zipp is wrong -- just that
the PDF lacks much explanation and seemingly makes no sense.

Even in their data- on the rider they mention this:
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Zipp Tangente Tires can save an additional 3-9 seconds or 1-3 watts).

So- zipp feels their non bearing data should also be falling in line with their max high side of 3 seconds/watt. hmmm and you were saying somthing about the above bearing data not equal to aero data and watts saved ?not? equalling the same time seconds? The numbers in the chart have increases completely inconsistent- as low as 2 seconds/watt (20->21 W = 1 W = 2 seconds = 2 Sec/Watt )... to the grandaddy of them all- (33 -> 35 W = 2 W = 10 sec = 5 sec/ watt ) so please explain why a watt can't be equal to seconds again??? We're talking about Power.


I'm not going to even get into test protocal- where they say the rider "averaged" 300 watts... probably using a watt measuring system that's +/- 1.5-2%... or that using humans on bikes to test wheels- even the slightest movement will change drag data... (that's why cervelo built a zabriskie model to test their frames and equipment- b/c humans are NOT always consistent- a tilt on the saddle, a head movement, anything moving differently) etc. It's nice to see real world data- but it should be taken with a grain of sand... especially the way it's presented.

http://www.trigearreview.com/...ticle.aspx?REVID=523


Last edited by: mlinenb: Apr 3, 08 5:45
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Re: Zipp Aero Data- finally- comparing data with rider [mlinenb] [ In reply to ]
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In Reply To:
Rappstar- first- maybe disclose that you are sponsored by zipp....? then... check out the following.
It says that in his signature, no? Seems like disclosure to me.


----------------------------------
Justin in Austin, get it? :)

Cool races:
- Redman
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Re: Zipp Aero Data- finally- comparing data with rider [mlinenb] [ In reply to ]
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In Reply To:
Rappstar- first- maybe disclose that you are sponsored by zipp....? then... check out the following.

okay- just look at the pdf... the rider data- and tell me what the seconds per watts, equal?

14->16 W = 2 W = 6 sec = 3 sec / watt
16->20 W = 4 W = 14 sec = 3.5 sec/wat
20->21 W = 1 W = 2 seconds = 2 Sec/Watt <---- maybe about right
21->24 W = 3 W = 8 sec = 2.66 sec/watt
24 ->26 W = 2 W = 8 sec = 4 sec/watt
26 ->27W = 1 W = 2 sec = 2 sec/watt
27->30 W = 3 W = 8 sec = 2.66 sec/watt
30 ->33 W = 3 W = 8 sec = 2.66 sec/watt
33 -> 35 W = 2 W = 10 sec = 5 sec/ watt <---- hyper inflated

The PDF makes no sense, since the seconds per watts are not uniform.
Unless I'm missing something -- I'm not saying zipp is wrong -- just that
the PDF lacks much explanation and seemingly makes no sense.

Even in their data- on the rider they mention this:
Quote:
Zipp Tangente Tires can save an additional 3-9 seconds or 1-3 watts).

So- zipp feels their non bearing data should also be falling in line with their max high side of 3 seconds/watt. hmmm and you were saying somthing about the above bearing data not equal to aero data and watts saved ?not? equalling the same time seconds? The numbers in the chart have increases completely inconsistent- as low as 2 seconds/watt (20->21 W = 1 W = 2 seconds = 2 Sec/Watt )... to the grandaddy of them all- (33 -> 35 W = 2 W = 10 sec = 5 sec/ watt ) so please explain why a watt can't be equal to seconds again??? We're talking about Power.


I'm not going to even get into test protocal- where they say the rider "averaged" 300 watts... probably using a watt measuring system that's +/- 1.5-2%... or that using humans on bikes to test wheels- even the slightest movement will change drag data... (that's why cervelo built a zabriskie model to test their frames and equipment- b/c humans are NOT always consistent- a tilt on the saddle, a head movement, anything moving differently) etc. It's nice to see real world data- but it should be taken with a grain of sand... especially the way it's presented.

http://www.trigearreview.com/...ticle.aspx?REVID=523


std aero ROT: 0.1 lbf drag (measured @30mph) ~=5W ~= 0.005 CdA ~=0.5 sec/km at TT speed

So 1W is about 0.1sec per km or 4 seconds over 40km ... unless you're riding very quickly or fairly slowly.

As I check I ran a baseline static speed/power case with 0.25 CdA, rho=1.2, m=80kg, Crr=0.004. At mid-range TT speed of 12.5 m/s (45 kph) the baseline power is 332.2W and the time 53:20. Note this neglects getting up to speed, hills, wind, turnarounds. Add 1 single W of power to 333.2 W and the time drops to 53:16 for a savings of 4-seconds -> exactly what the ROT suggests.

Re what Zipp has presented, have you considered the effects of simple rounding of power and time to the nearest integer?
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Re: Zipp Aero Data- finally- comparing data with rider [rmur] [ In reply to ]
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If your data is 4 seconds/watt- that is 33% higher than what zipp's research shows... so if YOUR data is correct- Zipp grossly underreported the benefits of purchasing their premium wheels. Why would any company do this? Unless... your data/assumptions are not 100% correct. Zipp's data- for example- on their tires- are a 3 fold range of 1-3 watts saved- that's a huge difference- and what's the margin of error on that testing... 1-2 watts ;)
Last edited by: mlinenb: Apr 3, 08 6:15
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Re: Zipp Aero Data- finally- comparing data with rider [mlinenb] [ In reply to ]
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In Reply To:
If your data is 4 seconds/watt- that is 33% higher than what zipp's research shows... so if YOUR data is correct- Zipp grossly underreported the benefits of purchasing their premium wheels. Why would any company do this? Unless... your data/assumptions are not 100% correct. Zipp's data- for example- on their tires- are a 3 fold range of 1-3 watts saved- that's a huge difference- and what's the margin of error on that testing... 1-2 watts ;)

I stand my calcs for the conditions I assumed. Please note the equations are NOT linear and the ROT only applies for small changes.

I honestly do not know what model Zipp are using. I assume they used FC's actual CdA and mass + bike with some assumptions about Crr and ... possibly wind.

They state the drag was measured at beta=10 degrees but I'm not sure what they incorporated into a model to calculate time savings per w. Was the 300W referenced for FC the model power or simply what he was turrning over at the LSWT erg?

Personally I'd rather just see bloody drag in lbf or gf @30mph and then anyone can simply translate that into conditions and power levels/speed time appropriate to themselves!
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Re: Zipp Aero Data- finally- comparing data with rider [mlinenb] [ In reply to ]
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The power saved doesn't scale linearly with time saving.

Remember the energy related to velocity³ equation? It's something like going from 9 to 12m/s requires a doubling of power.
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Re: Zipp Aero Data- finally- comparing data with rider [mlinenb] [ In reply to ]
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Disclose that I'm sponsored by Zipp? You mean the fact that it is listed in my signature line is not adequate?

I wasn't at the testing, so my answer is not necessarily right.

But a couple things to note:

First, something I missed last night, the 1080 is 8 seconds faster than the 808 when used in the rear configuration. The margin of difference is larger when you compare front wheels, as the frame has no interference. So 16 seconds is probably closer to that, which most closely mimics wheel-only testing (wheels are usually tested in a fork). So, perhaps Zipp should list the margin between all wheels in front and rear configuration, but that gets to be a bit confusing.

What you also don't see in that chart is the weighting metrics used for various yaw angles NOR do you see error bars. The wattage savings is obviously some sort of average over a range of yaws. They also base the data on a set of multiple runs with each wheels. There is going to be some rounding. There is going to be some margin of error. A lot of it has to do with the savings at various yaw angles. With these deeper wheels, you have a much larger savings at some of the higher yaw angles. I believe this is the case with the 1080, which actually outperforms a disc at many yaw angles, but then at the much higher yaw angles, underperforms against a disc once the spokes start to see a lot of air.

So maybe Zipp should include error bars, total number of runs done, mean variance, the weighting schema they used, and any rounding they did in their brochure. But that would make it a windtunnel whitepaper, not a marketing pamphlet. The data is presented in such a way to be comprehensible to a lot of people.

I also never said bearing data in terms of watts-secs didn't match up with aero data. I said bearings do not see any yaw. The savings of better bearings at 5deg of yaw is the same as at 15deg of yaw. THAT is what you don't see with wheels. The savings of a 1080 vs an 808 at 5deg is not the same as it is at 15deg.

And, why does Zipp underreport if rmur is correct at 4sec/watt? Because people have hard time with 3 sec/watt, so I'd underreport too. They are being more conservative in their estimates, which I actually know is a fact, because people have a hard time grasping the savings they do report. So they round down to be safer.

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp
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Re: Zipp Aero Data- finally- comparing data with rider [rmur] [ In reply to ]
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std aero ROT: 0.1 lbf drag (measured @30mph) ~=5W ~= 0.005 CdA ~=0.5 sec/km at TT speed

So 1W is about 0.1sec per km or 4 seconds over 40km ... unless you're riding very quickly or fairly slowly.

As I check I ran a baseline static speed/power case with 0.25 CdA, rho=1.2, m=80kg, Crr=0.004. At mid-range TT speed of 12.5 m/s (45 kph) the baseline power is 332.2W and the time 53:20. Note this neglects getting up to speed, hills, wind, turnarounds. Add 1 single W of power to 333.2 W and the time drops to 53:16 for a savings of 4-seconds -> exactly what the ROT suggests.

What, you don't trust me? I'm hurt! ;-)
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Re: Zipp Aero Data- finally- comparing data with rider [mlinenb] [ In reply to ]
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Wow, this is definitely not how I envisioned the discussion on this going down. To start with, the rounding errors in the method Mark is using to compare the data is what are hyperinflated. By comparing the delta time between runs, you are dividing relatively small numbers and getting relatively misleading delta watts. This is the type of thing that companies can (and do) do to make their products look good if they choose...but you see what we have actually done is use the rule of thumb that 1w=3s, and divided the total time savings (which itself was calculated directly from tunnel measured CdA) by 3. Using that method our chart breaks down like this:

42s/3=14w (claimed 14w)
48s/3=16w (claimed 16w)
62/3=20.66w (claimed 20w)
64s/3=21.33w (claimed 21w)
72s/3=24w (claimed 24w)
80s/3=26.66w (claimed 26w)
82s/3=27.33w (claimed 27w)
90s/3=30w (claimed 30w)
98s/3=32.66 (claimed 33)
108/3=36w (claimed 35)


So in every instance except 1, we have actually rounded down, and in the one we rounded up, it was up by 0.33 watts...and I'm not mentioning that we also rounded the time savings in second down as well. This is an excellent lesson for all of us in how easy is can be to manipulate a data set simply by the way you choose to analyse the data.

On top of that, we using a very low rule in saying that 1w=3s. Anybody can go to analytic cycling can run numbers and see that 1w is generally going to equate to 3.5=4.5 seconds for most any condition...but we choose a low number to avoid looking as if we are trying to inflate the numbers upward, and we have been asked by Fabian and CSC not to use the actual number we use in our computer models for Fabian, as that piece of data combined with this info could allow somebody to back-calculate Fabian's CdA...which as you can imagine is a bit of a secret.

As for the arguments about the rider wattage influence on the data. we use 300 watts rider output for athletes in the tunnel as that is an output that is high enough to make the rider sit on the bike and pedal in a way similar to what is realistic, but low enough that he can repeat it numerous times without fatiguing, which generally leads to position changes over the course of a test like this...if we made him pedal at his full TT output, we would definitely struggle with repeatability toward the end of the data set...remember, this sort of data set takes hours to create! So ultimately the 300w and the power meter used has no influence on the data, as the time savings is calculated directly from CdA comparisons using a formula long relied upon by pretty much everybody who does this sort of testing daing all the way back to Chet Kyle and Jim Martin. As for data quality, these CdA values are calculated from average CdA taken for a 1 minute interval at 100hz, so each data point is the average of 6000 measurements, and each point much also satisfy a std deviation criteria for those 6000 points, such that the data point is thrown out and recreated if there appears to be drift or abnormally high deviations within the set (fabian is amazingly stable and we only had to recreate 1 point)

Lastly, in correlating stand alone wheel testing to in bike testing, we have always maintained a reduction coefficient on rear wheel efficiency..and acknowledge that there is also a coefficient for the front wheel depending on fork. This coefficient currently exists in analytic cycling, and is also a rule of thumb value for drag reduction on the rear wheel caused by frame and rider. This number is different for every frame and is also different for wheel in frame only vs wheel in frame with rider as the rider adds additional shielding to the rear wheel. So the argument about the 808-1080 rear wheel being worth 8 seconds in the chart vs 16 seconds in the wheel only data is pretty much exactly as one would expect, with the 16 seconds being spot on for a front wheel and the 8 seconds being about right for a rear in this situation, which was rider on bike at 10 degrees...for this bike w/rider at that angle a 50% reduction coefficient is pretty accurate...note that in the last 2 data points the 1080 front vs 808 front is worth 14 seconds...which is pretty darn accurate to the wheel only data considering all of the added complexity in the system.

Look we certainly aren't claiming to be perfect or to have perfect methods or perfect data, but like any sort of testing, there are always tradeoffs. We will never stop wheel only testing as it is the best way to determine small variations between prototypes, as well as it allows us to look at things more than just drag, mainly side force, stability, and stall performance, all things that are lost in more complex systems. We have even been talking with the LSWT about ways to improve the balance system so we can get individual component drags from more complicated systems...this is currently done using stings at the ARC wind tunnel about 3 miles from our offices here in Indy (too small and fast for bikes)...and could be very interesting for cycling...but at this point is very cost prohibited and still won't solve the question of rider or no rider for product testing. But like anything esle, nothing will be perfect, just like the cervelo tunnel dummy gives high repeatability, but can't offer real world flow conditions on the rear half of the bike due to being static (a condition we also experienced when we used a dummy during development of the zipp 2001 in the early 1990's), our system of doing wheel only, wheel in fork, wheel in bike and wheel with rider (a system that nobody else even attempts) still has flaws as it cannot accurately replicate any fork or any bike....but what it can do is tell us the relative trends between designs and concepts, and it can help us build more accurate math models for converting wheel only data into time/wattage data for our athletes...and in the end I don't think anybody does as much to contribute to the available data and discussion on this topic as we do...and hopefully that is worth something to all of you...

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc
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Re: Zipp Aero Data- finally- comparing data with rider [joshatzipp] [ In reply to ]
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Josh - 2x comments if I may:
1) Why are CdAs quite so secretive? I can see why you don't give CdAs sufficient that we can all work out numerical drag differences between positions, but can you not even give data from an undisclosed previous date so some of us have some numbers to play with?

2) Can you possibly give me an idea of CdA of a pro cyclist. I was using 0.8 as that's what bicycling science said, but most reports I've read said 0.9. Just a generic value for a good position. Please? *puppy dog eyes*

Just because some people slate your data that doesn't make it bad. I purchased your wheels (and thus didn't eat for months) because you publish data. Keep it coming please!
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Re: Zipp Aero Data- finally- comparing data with rider [zebragonzo] [ In reply to ]
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2) Can you possibly give me an idea of CdA of a pro cyclist. I was using 0.8 as that's what bicycling science said, but most reports I've read said 0.9. Just a generic value for a good position. Please? *puppy dog eyes*

Kyle published data a long time ago that would put Cd (which seems to be what you're really asking about, not CdA) in the 0.65-0.75 range (depending on yaw angle) for someone in the aero position.
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Re: Zipp Aero Data- finally- comparing data with rider [Andrew Coggan] [ In reply to ]
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Sorry, you're quite right Andrew; I was after Cd.

The problem is that the data you're refering to is from 1989 I think; cycling science, 1st edition, aero bars and helmets (or some such title) and I was after something with modern kit.

Reference values and improvement of aerodynamic drag in professional cyclists (Journal of Sports Sciences, Volume 26, Issue 3 January 2008) and based on the old Kelme team, indicated a Cd of 0.9ish.
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Re: Zipp Aero Data- finally- comparing data with rider [zebragonzo] [ In reply to ]
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In Reply To:
Sorry, you're quite right Andrew; I was after Cd.

The problem is that the data you're refering to is from 1989 I think; cycling science, 1st edition, aero bars and helmets (or some such title) and I was after something with modern kit.

Reference values and improvement of aerodynamic drag in professional cyclists (Journal of Sports Sciences, Volume 26, Issue 3 January 2008) and based on the old Kelme team, indicated a Cd of 0.9ish.

AFAIK, you can't practically separate the two (for the bike/rider ensemble) so why worry about Cd in isolation?

thinking about it: I figure Obree probably had the lowest going for the egg or Superman. Something around 0.55 in the Padilla et al Indurain Hour record paper.
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Re: Zipp Aero Data- finally- comparing data with rider [rmur] [ In reply to ]
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Capelli et al got about 0.22 as a CdA for the Obree. Pretty similar to the CdA of a rider in the who-cares-if-I-die descent position (Kyle & Burke 84)

Regarding separation of Cd and A; Cd is very helpful as it tells you a lot about the shape of a body. Cd and A separately are far more helpful.
Last edited by: zebragonzo: Apr 3, 08 8:39
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Re: Zipp Aero Data- finally- comparing data with rider [zebragonzo] [ In reply to ]
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Sorry, you're quite right Andrew; I was after Cd.

The problem is that the data you're refering to is from 1989 I think; cycling science, 1st edition, aero bars and helmets (or some such title) and I was after something with modern kit.

Reference values and improvement of aerodynamic drag in professional cyclists (Journal of Sports Sciences, Volume 26, Issue 3 January 2008) and based on the old Kelme team, indicated a Cd of 0.9ish.
I haven't had a chance to read that paper yet, but what do you suppose accounts for the difference: UCI rules, the refusal of many European pro roadies to get serious about aero positioning, or the use of sub-optimal TT equipment by the Kelme riders?
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Re: Zipp Aero Data- finally- comparing data with rider [zebragonzo] [ In reply to ]
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Capelli et al got about 0.22 as a CdA for the Obree. Pretty similar to the CdA of a rider in the who-cares-if-I-die descent position (Kyle & Burke 84)

Regarding separation of Cd and A; Cd is very helpful as it tells you a lot about the shape of a body. Cd and A separately are far more helpful.
hmmm .... I can see that for a 'bluff body' but a bike & rider is such a mess of different shapes, some rotating relative to the airstream, some fixed ... etc. What does overall Cd and overall A tell you that overall CdA does not? just wondering what your application is?
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Re: Zipp Aero Data- finally- comparing data with rider [rmur] [ In reply to ]
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I figure Obree probably had the lowest going for the egg or Superman. Something around 0.55 in the Padilla et al Indurain Hour record paper.

I'd forgotten that Padilla et al. had estimated Indurain's Cd...
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Re: Zipp Aero Data- finally- comparing data with rider [Andrew Coggan] [ In reply to ]
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In Reply To:
In Reply To:
I figure Obree probably had the lowest going for the egg or Superman. Something around 0.55 in the Padilla et al Indurain Hour record paper.

I'd forgotten that Padilla et al. had estimated Indurain's Cd...

see ... you clearly can't be trusted :-) Neither can I, as the paper actually suggests 0.50 for the Egg and 0.55 for the Superman and .... for comparison Merckx at 0.75.

I guess these are all actually at a track-weighted average yaw angle - around five degrees or so.
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Re: Zipp Aero Data- finally- comparing data with rider [rmur] [ In reply to ]
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I'm investigating the praying mantis position and you'd be shocked how many people say something like:
"Well my frontal area dropped by Xm² thus my drag will drop by X newtons as Cd will remain the same"

Basically, I want to know what happens to Cd as the mantis position is adopted!
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Re: Zipp Aero Data- finally- comparing data with rider [rmur] [ In reply to ]
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In Reply To:
the paper actually suggests 0.50 for the Egg and 0.55 for the Superman and .... for comparison Merckx at 0.75.

Hmm. Sounds to me as if the values are underestimated across-the-board.
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Re: Zipp Aero Data- finally- comparing data with rider [zebragonzo] [ In reply to ]
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In Reply To:
you'd be shocked how many people say something like:
"Well my frontal area dropped by Xm² thus my drag will drop by X newtons as Cd will remain the same"

I think you should bring this topic up for discussion on www.biketechreview.com.
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Re: Zipp Aero Data- finally- comparing data with rider [Andrew Coggan] [ In reply to ]
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I have!

Sorry for hijacking the thread; back to Zipp are rubbish and they lie and they use actual kitten blood to make their wheels go fast. Or something.

PS. I'm still after a Cd if possible Josh :-)
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