November in the wind tunnel: "semi-aero"

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Tunnel testing alloys was actually more exciting for us than it should have been.  While a lot of people choose to buy builds from us with the rims on test, this essentially amounts to a "public good" test, simply because these rims are so widely available.  The excitement mostly came from the fact that the internet was seemingly ready to have an aneurism there was so much demand for us to do this (which is a funny concept when you think about it - no one else spends the money to do this for people, not even the rim makers), and because so many "eyeball wind tunnel" experts had definitively pronounced the results long ago. 

We have to once again stress that directly comparing this test on this day with that test on that day is a fool's errand.  The way that we have designed our testing protocol, we will always be able to make significant back-references, but direct comparisons between different tests are worthless. Relative results of one wheel vesus another from test to test are valuable, which is why we have tied ourselves to the benchmark of the 404 wheel we used in our original test.  We will always keep that wheel as the reference standard. 

We tested these with a 23mm Continental 4000s II tire - one tire used in all tests, as it must be. That is perhaps the most popular tire used with the rims we tested, and is a standard for the wind tunnel.  Significantly, you must take note of the tire width as it is on each wheel when looking at these results.  The same tire will inflate differently on different rims: the wider the interior dimension between the brake tracks, the wider the tire will set up.  Among the rims in this part of the test, the differences are fairly small.  As we get into other rims, this difference will become more significant. 

 The biggest lesson out of this test is how much closer the Kinlin and Pacenti rims come to the performance of carbons than what the A23 did.  The overall delta between worst and first in this test was much smaller than it was the last time.  Tony Martin's not going to read this and think "you know, maybe I ought to use some nice mid-depth alloys in my next time trial," but the gap is much smaller.  Again, we are only able to make this statement because the A23 was tested against our reference wheel using the same tire (although we used a different type of tire last time), and the same reference wheel was used to measure the gap this time.  There is the noise of "maybe that's just a particularly bad tire for the A23" in there, but that's at most a very small part of the story.  Using our back-check method, the Rail 34 is faster than an RFSC38, while the alloys in this test are slightly slower.  

The Kinlin was the faster alloy.  As we will explore later, the tire's increased width on the Pacenti may account for all of the difference between the two.  It is impossible to normalize one tire to the same width on two different rims, and you wouldn't want to anyway.  What you could do is test a narrower tire on the wider rim and interpolate from there, but with these rims we were more interested in seeing if there were any gross differences between the two, and how they stacked up compared to the carbons on test.  We will explore the effect of inflated tire width in more detail in subsequent posts. 

 


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  • Will on

    I'm a little confused with the first chart because I have no idea what does the x and y axis mean.

  • Dave K on

    Thanks for the comments everyone. Mario – That would have to be measured. Nothing I've ever seen suggests that weight on that order of magnitude makes much perceptible difference, but we are going to try and take our own stab at it in the near future. Not this week.pyf – For this chart and others, we use the AoA-weighting protocol developed by Tour magazine. This protocol recognizes that as you travel at higher speeds, the lower angles of attack are more relevant, and as you slow down, the angles of attack broaden. We do this because we believe in it, not because it makes our wheels look better (which it doesn't do). We will include all relevant objective data on wheels used (some of it is part of what we learned and the story behind it that we are developing, so we aren't going to just vomit up a large chart for now), but we (you and I) have had the discussion recently that you can not reference un-linked tests. How many grams of drag wheel A did on March 2nd is not comparable to what company B did on April 12th. There are too many variables there. I spent most of Tuesday switching tires from wheel to wheel so that each wheel setup used the same tire – we had ONE 23mm tire and ONE 25mm tire. Run wheels with different tires, even if they are the same brand/model/width, bought in the same store on the same day, you have an invalid test. Literally, anything we can do to discourage people from making the comparison you're after, we're going to do. Two companies that test against a common wheel like a 404 can be compared against each other, TO A LIMITED DEGREE, but without a common wheel, nope. It's hard as hell to find a creditable direct comparison of 404 versus 303, so the two are not linked. Now you even have to specify which 404. 16 or 18 spokes? Ours is 16, because that was the model at the time we did our first benchmark test, and we are referenced to that specific wheel. It's quite a good bet that 18 is at least ever so slightly slower. Firecrest or Firestrike? Firestrike has a different internal width, and anyone who wants to bet against me that Firestrike is a small bit slower in the tunnel (but also probably overall a better wheel) than Firecrest, I'll take that bet. Do not compare tests that are not directly linked to one another, period, end of story. another dave – Thanks. People's opinions take a ton of time to change. Think of how long the paradigm of 19mm tires for TT lasted, the collective subconscious thought they "looked" aerodynamically faster. Now a big huge tire "looks" aerodynamically faster. We tested it and now know the answer of what's aerodynamically faster, so far as we measured. And our measurements certainly make an exceedingly strong general implication. In any discussion about quantifiable things, we much prefer to be the guys with the actual info as opposed to the dogmatic and strongly held opinions.

  • another dave on

    re: why bother? Hey Mike, just wanted to clarify my prior post. "Why bother?" was a bit facetious. I know you guys bother because you have a passion for what you do, you take pride in your work, and you wanna spread the luv. So spread that luv already, dammit…

  • pyf on

    Thanks for sharing those first results ! Looking forward to seeing the next ones :-) .Couple of questions if you don't mind me asking :1) when you calculate seconds saved at different speeds, how much importance do you give at each yaw angles, is it something like 10% 0° + 15% 2.5° + 25% 5° + 20% 7.5° + 15% 10° + 10% 12.5° + 5% 15° … well I don't know what the exact numbers are but just wondering if you average this way ?2) do you think you could provide for each wheel tested (all front wheels ? so when you say Enve 3.4 it's actually Enve 3 being tested ?) hub use, number of spokes, spokes type, nipples (internal or external), internal rim width, width of tire tested on the particular rim ? Maybe you could create a little tech sheet with a picture of each wheel and the techniical information next to it ?3) if we look at three wheel manufacturers who tested at A2 Wind Tunnel (with results widely available) with the same tire : Flo with GP4000S 700×23 "1", Boyd with GP4000S 700×23 "1" and November with GP4000S 700×23 "2", you are the only one providing the Y axis with watts of drag, If you use the same setup and can provide the same graph with grams of drag then it makes the information even more valuable (considering there is also the ZIPP 303 firecrest on the Boys results, etc.). Just saying… ;-) .Thanks a lot in advance for your answer !

  • Mario on

    Wow! In other words…at speed the kinlin would be faster…but due to the lighter weight of the pacenti, it rolls up to speed faster ….I don't think you could feel that roll up difference from a dead stop….how many grams are we talking about? 60 +- grams? I don't know if I'm numb or what…but the only time I could feel a roll up difference from a wheel, is if the rear wheel is at least 100 grams lighter…What about momentum and weight? Will a slightly heavier rim ( using same spokes and hub) roll/ slow down longer? That seems to be the case when it's on my truing stand…



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