Sunday, January 22, 2017

Getting Caught Up II's been awhile. Lots of things happening in the last year.

Anyway, It's time to get caught up. Although this tire rolling resistance data was published last spring after I did a collaboration with Jon and Chris of Flo Cycling (see report here), I have been remiss in adding it to the spreadsheet linked to on the right side of this blog. These are tires I roller tested for the Flo tire aero study, models of which I had not already tested. Here are the additions from that testing:

Continental GP4000SII   25C = .0031, 28W for pair @ 40kph
Continental GP Attack   22C  = .0033, 31W for pair @ 40kph
Continental GP4000SII   23C = .0034, 31W for pair @ 40kph
Schwalbe One Tubeless 25C = .0037, 34W for pair @ 40kph
Schwalbe One Tubeless 23C = .0041, 38W for pair @ 40kph
Felt TTR1                      23C = .0048, 45W for pair @ 40kph
Continental Gatorskin     25C = .0048, 45W for pair @ 40kph
Continental Gatorskin     23C = .0052, 48W for pair @ 40kph

The interesting points in there for me are the confirmation that the GP4000SII rolls the same as the previous GP4000S, plus how poorly the Gatorskin models roll at 17-20W worse than the GP4000SII for a pair at 40kph. Wow.

Additionally, in August of 2016, I finally got around to testing a pair of tires that Eric Reid had sent me. One was a brand new model of the Continental Force tire (I had only previously tested a lightly used one) and also a Continental GP TT tire. The latter is a tire that hasn't had much test data on it, so it's something I really wanted to see. Here are those results:

Continental GP Force   24C = .0030, 27W for pair @ 40kph
Continental GP TT       23C = .0028, 26W for pair @ 40kph

That result for the GP TT makes it the new "top dog" for brand new tires I've roller tested. One caveat on that tire measures much larger (24.6mm) than it's rated 23C on my narrow Mavic Open Pro rim, or nearly 2mm wider than a Continental SuperSonic 23C (22.8mm) on the same rim, and is only .0001 lower Crr (~1W difference at 40kph for a pair, or what I consider "tied").

Finally, in October of last year, I roller tested a couple of other tires. One was a newer version of the Continental 20C SuperSonic. I was interested to see if, like some of Conti's other tires, it had gotten any faster since I had last tested that model in 2012.  It did. Here are the results:

Continental SuperSonic 20C = .0030, 28W for pair @ 40kph

That's a fairly significant change from the previous measurement of .0034 for that tire, and corresponds to an improvement of ~3W @ 40kph for a pair, and is just as fast as many tires of MUCH greater width.

The other tire I tested in October was the Specialized S-Works Turbo Tubeless 26C model. This tire was interesting to me because it had been getting some "buzz" about how it was a super-fast tubeless tire (most aren't up to this point).

In this case, I tested it both with a latex tube inside, and then also set up tubeless, with Orange Seal sealant inside (~20ml). Both tests measured nearly exactly the same (within less than .0001 Crr) with the result being:

Specialized S-Works Turbo Tubeless 26C = .0032, 30W for pair @ 40kph

Although that's relatively fast for a tubeless tire, it's not the world-beater it had been hyped to be...especially considering that it's mounted width on my Hed Jet+ wheel for that testing was nearly 30mm!

Anyway...good to be back at it, and I've got some other fun stuff (not so much tire related, hopefully) to be sharing with all of you shortly. Again, all of these updated entries are in the spreadsheet link in the upper right of this page.

edit 23Jan2017: After roller testing a newer version of the Continental SuperSonic in 2016 as described above, I decided to use the newer value in calculating the total power for the H3/Conti 20C SS combination in the chart shown in my last "Win Tunnel Playtime" post. With those changes, the chart looks as follows, and it appears the old H3 has some pretty good speed in it still with that tire:

Sunday, March 6, 2016

Win Tunnel Playtime - Part 3 (The "After Party")

About a week after the fun session in the Specialized Win Tunnel (outlined in Part 1 and Part 2), I received an email from Cam Piper which included "wheel only" data for the Roval CLX64 wheel and each model size of both the S-Works Turbo (22C, 24C, 26C, and 28C) and Turbo Cotton (24C and 26C) tires. At the time I visited I had asked about this data set, and although they had all the data, it wasn't easily collated into a single file. So, on the following Friday, Cam took on the (large) task of running and procuring a dataset for all of those tires in a single session. That data is summarized in the CdA vs. yaw angle plot below:

Roval CLX64 Wheel

As one can see, that's a really nice data set, especially the symmetry. Also, one can clearly see the effect of tire size on drag, especially with the S-Works Turbo sizes. In regards to size, it's important to note that the listed tire sizes typically "grow" by ~2mm when mounted to a wheel with such a wide interior bead width, such as the Roval CLX64 (nearly 21mm, if I recall correctly). For example, the 22C S-Works Turbo actually measured slightly >24mm wide when installed on that wheel.

Not long after receiving this data, I also received a box from Specialized containing samples of each of the listed tires for me to roller test personally for Crr.  Wow...that's a lot of tires to test, plus at the time I didn't have a bike capable of testing the 28C S-Works Turbo when mounted on a wide rim. Luckily, I was in the process of building up a "gravel bike" (based on a 26" rigid MTB frame...I digress...) and so eventually I could get the Crr data for that one as well. 

When the tires arrived, I realized that it may be time to revisit my tire testing protocol and tweak things to make the process more amenable to testing wider tires. When I started roller testing tires, I was mainly looking at TT tires and wheels of the time were still significantly narrower than they are today, so testing at 120 psi seemed reasonable. However, as rims and tires have gotten wider, I've been uncomfortable with pumping tires like 26C and 28C models up to 120 psi to test...and in fact, have had a couple cases where I couldn't get tires that wide to stay on the rims when inflated! Knowing that, while testing this batch of Specialized tires I decided to do some narrow (Mavic Open Pro) vs. wide (Hed Jet+) rim testing along with tests at 120 psi and 100 psi. To make a long story short, I found that in general, a tire will roll approximately the same on my rollers on a narrow Open Pro rim at 120 psi as it will on the extra wide Jet+ rim at 100 psi. That was a valuable thing to discover, and it means that my future tests will be run at 100 psi on a 20.5-21mm internal width diameter rim. I especially wanted to test all of these tires on a wide internal width rim for Crr so that it would best match the tires as mounted on the Roval CLX64 wheels used in the aero testing.

The Crr results for the 6 Specialized tires are as follows:

Specialized S-Works Turbo 22C = .0041, 38W for pair @ 40kph
Specialized S-Works Turbo 24C = .0036, 33W for pair @ 40kph
Specialized S-Works Turbo 26C = .0035, 32W for pair @ 40kph
Specialized S-Works Turbo 28C = .0035, 32W for pair @ 40kph (note: AC101 disc wheel)

Specialized Turbo Cotton 24C = .0029, 27W for pair @ 40kph
Specialized Turbo Cotton 26C = .0028, 26W for pair @ 40kph

By comparison, here's the results for the "benchmark" GP4000S (tested on Open Pro @120psi):

Continental GP4000S 23C = .0034,  31W for pair @ 40kph

There are a couple of interesting takeaways in those results. First, I was somewhat surprised at the seemingly non-proportional "hit" in Crr the 22C S-Works Turbo took in comparison to the 24 and 26C sizes. It was also interesting that 28C size basically rolled the same as the 26C size, although that may be attributable to the fact the 28C was tested on a low profile, 32 round spoke disc brake wheel, while the 26C was tested on a Hed Jet6+ deep wheel with bladed spokes. One other interesting result is that in the Turbo Cottons, the 26C tire rolled only slightly faster than the 24C. This may mean that the Crr of that tire model is driven more by the tread composition (both tires appear to use the same width tread) than by the casing material properties. Lastly, these results appear to confirm that the S-Works Turbo tires in the 24C and 26C sizes are basically "tied" with the Continental GP4000S in terms of Crr (remember that I consider anything within .0001 of Crr to be "tied")., if any of you have read some other blog posts of mine, you probably know where this is going.  Yep...what does it mean when we combine the Crr and CdA results? Which of the tires above gives the best combination of rolling resistance AND aero for a particular application? 

Well, to truly get at that answer requires some fairly detailed modeling, such as that performed by, for example. However, it's possible to at least get an inkling of which tire may give the best combo using some simple assumptions.  In this case, I made the assumption that the wheel load is 38kg (~45% of my typical "all up" mass of 85kg, typical of a front wheel for me) and a ground speed of 35 kph (~22 mph).  Figuring out the power for each tire at that speed is easy, and is merely Crr x Speed x Mass x gravity.

The expected power for the aero drag is slightly more difficult...and involves using the apparent wind speed expected for the particular ground speed AND yaw angle. It's probably easier to explain with some vector diagrams (and I'll do that if the interest is shown), but suffice to say that if your ground speed is 35 kph AND you have a non-zero yaw angle, then the apparent wind acting on the rider is going to be greater than 35 kph. It's important to remember that the results coming from a wind tunnel are the CdA (or sometimes grams of drag) in the body axis of the wheel, or bike, for a given APPARENT wind speed (typically set to ~30mph for better resolution). So, what that means is that there is some trigonometry that needs to be undertaken for non-zero yaws for the power calculation. In this simplified analysis, it's also an assumption that any sidewind is a "pure" crosswind, or oriented 90 degrees to the riders travelling path. Thankfully, the data acquisition setup at the Specialized Win Tunnel already does that trigonometry for us. This is sometimes referred to a "beta correction" in wind tunnel parlance.

So, I set up a spreadsheet to handle all of that, and here's the expected combined power for a single wheel with a 38kg load, travelling at 35 kph.

Roval CLX64, 38kg load, 35 kph ground speed

So, what can we take from that plot? As I've said previously, "Low rolling resistance can make up for a LOT of 'aero sins' " (Here, and here)...and that plot above helps bring that home. Although the S-Works Turbo 22C tire was the clear leader in the CdA plot, when combined with the expected Crr of the tires, it actually isn't as good as any of the other tires at 10 degrees and below of yaw angle.  In my view, the Turbo Cotton tires are the clear winners in the combined power plot, with the edge going to the 24C version, at least in my mind. The total power at 0 and 5 degrees are basically identical, but the 24C has a slight edge at 10 degrees. At 15 degrees, the 2 tires are tied again.

In looking at the S-Works Turbo tires only, it appears that the best overall of the bunch is the 24C model, with the 26C nearly tied with it.

Now obviously, that's the results for that given load and ground speed. For different wheel loads, the Crr contribution is going to vary proportionally up and down relative to the load, and for different ground speeds, the aero proportion is going to vary with the cube of the ground speed up and down. So, for lighter and/or faster riders than what is assumed, the aero effects will be relatively more important, while for heavier and/or slower riders the Crr effects will be relatively more important.

After calculating these results, of course I also applied them to the wheel and tire combos that were taken during my Win Tunnel visit.  To remind everyone of the CdA plot of all of the combos looked, here it is again:

Combining that plot with the Crr results like we did above, results in the following overall expected power plot:

I think I'll just leave that there without further comment...Enjoy!

The spreadsheets containing the data and calculations can be viewed here:

- Roval CLX64 plus Specialized Tires

- All wheels from Win Tunnel Visit

edit 23Jan2017: After roller testing a newer version of the Continental SuperSonic in 2016, I found that it had significantly improved the Crr in comparison to the c2012 version I had previously tested. So, I decided to use the newer value in calculating the total power for the H3/Conti 20C SS combination in the chart above.  With those changes, the chart looks as follows:

Sunday, October 25, 2015

Win Tunnel Playtime - Part 2

In the previous blog post (Win Tunnel Playtime - Part 1), I described how this particular adventure came about, and I presented the bulk of the data collected, which was the result of a large amount of wheel and tire testing. In this post, I'll be covering the remaining testing we did on that day. In short, we did a small number of bike-only runs, varying the front wheel on the bike. This was done in an attempt to see how the differences in drag compared to the wheel-only runs for changes in front wheels. Most of the testing was done using my personal bike (a Stinner Frameworks custom steel road frame), and for comparison sake, we also tested a brand new Specialized Venge ViAS which just happened to be available <smirk>.

So...let's get to it. Shown below is a summary plot of all of the bike-only runs. As a bit of explanation, the combinations tested were as follows:

  1. Stinner with Hed Jet6+ wheels and 24C Specialized Turbo Cottons. Specialized Virtue bottle. This setup represents my own personal rig, set up in what I like to call "crit mode".
  2. Same as #1, with front wheel swapped for a Roval CLX64 with a 22C Specialized S-Works Turbo tire.
  3. Same as #1, but with front wheel swapped for Flo 90 with 23C Continental Super Sonic tire.
  4. Same as #3, but with round bottle and bottle cage swapped over from Venge ViAS frame on downtube (low location).
  5. Venge ViAS with Roval CLX64 wheels, 22C Specialized S-Works Turbo front, 24C rear. Round bottle on downtube.

Aside from how impressively low the drag is for the Venge ViAS in that chart above, what is particularly interesting is how those 3 upper plots (with the same bottles on the bike) compare to each other, AND to the wheel-only data. To do that comparison, I looked at the differences seen between those particular combinations of wheels and tires during the wheel-only testing and compared them to the bike testing.  Those comparisons are summarized in the following 3 charts.

What we can see from the above is that in most cases the differences in drag observed from wheel only data are within 0-.002 m^2 of the differences observed when those same wheels are swapped for the front wheel in a bike. There are a couple of differences that vary by .003m^2 in that data, but overall I'd have to say that the "predictive" utility of how a front wheel will perform within a bike based on wheel only data is pretty good.

Now we get to the part where we put a "floppy human" (me!) on board and see what happens.  Due to time constraints, for this portion of the data gathering we only took 2 yaw data points (0 and 10 degrees), which each consisted of 60s of sampled data. Since the Venge ViAS was there (and in my size!) of course I made sure to get a set of runs in on that. Since the Venge was the last bike from the bike-only runs and was already mounted to the tunnel balance platform, that was the first up.

Next was the Stinner with the Hed Jet6+ and Turbo Cotton tires (in my "crit setup")

And finally, we swapped the front wheel for the Roval CLX64 and 22C S-Works Turbo.

Here's how that all played out:

As you can see, the difference at zero yaw between the Roval wheel and the Jet 6+ (as configured) was ~.003 m^2, which compares pretty favorably with the ~.002-.003 m^2 observed in the wheel-only and the bike-only testing for those combinations.  

At 10 degrees of yaw, the difference appears to be somewhat larger, with the bike-with-rider testing showing a difference of ~.012 m^2 whereas the bike and wheel-only testing was more like .006-.007 m^2 of difference observed.

What's truly interesting though, is how closely the overall drag was brought together between the Stinner and the Venge ViAS when a rider is on board. At zero and 10 degrees of yaw, the drag difference appears to be less than half of what was observed in the bike-only testing. This puts my overall drag when on the Stinner to within .004-.006 m^2 of what it was on the Venge ViAS at zero and 10 degrees of yaw. Obviously, there must be something going on with bike interactions near the rider. Also, it's important to point out that the comparison between the bikes wasn't completely "apples to apples" since the water bottles were different. However, the Venge ViAS is designed to be basically "bottle neutral", so that's not too big of a factor. Another difference was that the bars were not identical, neither in model or in width. But again, the bars on the Stinner, although slightly narrower (40 vs. 42 for the Specialized bar) also have drops which are, that probably ends up being a "wash" in the bike-only testing.

So...another large dump of data...with a few good conclusions. It appears that when making changes to the "leading edges" of the bike equipment (such as wheels, forks, bars, etc) drag differences observed in component-only and bike-only testing "hold" when applied to testing with a rider on board, at least for near zero yaw.  However, that probably can't be said for pieces of the puzzle that are further back in the flow and interact more closely with one another.

As always, if you have any questions, just fire away in the comments...oh, and the data for this portion of the testing is found here: Bike and Rider data

Monday, October 5, 2015

Win Tunnel Playtime - Part 1

As I mentioned in my last post, thanks to the generosity of Specialized, Chris Yu, and Cam Piper (both pictured above), I recently had the opportunity to spend a day in Morgan Hill, CA at Specialized's Win Tunnel facility. You're probably asking "How did THAT happen?" (something I asked myself repeatedly)...and well, it's a long story. I had met Chris Yu a few years back when I had the opportunity to observe the wind tunnel testing of my friend and professional triathlete, Jordan Rapp. At the time, Specialized had recently opened their "Win Tunnel" facility and I had a great time watching the proceedings and trying not to be too annoying in peppering Chris and Mark Cote with questions. Since that time, Chris and I had "conversed" on various forums, and even swapped a few emails.

Earlier this year, Chris had sent me an email asking if I was interested in participating in one of their videos that they occasionally produce. I jumped at the opportunity and said "Sure!" and we planned on doing something in the July/August time frame. thing led to another, and the planned purpose of the video was changed...and then it turned out the video team wasn't going to be available on the dates we had planned. No worries though. As Chris explained to me, the tunnel time was already blocked out, and it turns out that like most forward thinking companies based in the SF Bay area (i.e. Google, Apple, etc.) Specialized allows their engineers time to "play", or pursue subjects that may not have an immediate application...on the thought that this "playtime" may spark some unexpected innovation. Chris told me we could brainstorm and come up with some things to look at, and like most tests, we'll most likely come up with some answers, but also some good additional questions to pursue. Sweet. How could I say no?

Due to the VERY large amount of data collected, what you'll see here in Part 1 is mostly the results of the morning of testing on that day in the Specialized Win Tunnel. I came up with the idea of trying a host of wheel and tire combinations, and then following it up with some of those same wheels and tires in bare bike tests...and then finally, I was hoping to get into the tunnel on a bike myself for a few runs. Shown below are the wheel/tire results. Part 2 (coming later) will show the remainder of the data. The idea was to see what sort of info could be gleaned about how wheel and tire combos are affected by the tire mounted (especially width) and if the differences observed "carried through" to both bare bike testing and testing with a rider. It was an "ad hoc" plan and group of equipment, but I figured at a minimum I would be getting a crash course in wind tunnel testing and the difficulties of doing so.

What you see above is the test matrix I put together for the wheel and tire testing. The wheels listed in the column on the left are the ones I would had available to me, and run the gamut from shallow to very deep. Across the top are listed the tires. Knowing that there was a limited time for the wheel/tire runs, I decided to go for a mix of tires on the wheels, with the one I was most interested in seeing was the one in the first column, the new S-Works Turbo 22C model. The greyed cells are the combinations tested, with the number in front of the hyphen the order in which they were to be tested. I wanted to make sure we weren't wasting time waiting for a tire to be swapped for a run.  The number after the hyphen is the measured width, as mounted.

So, let's get to the data...but, before we do that, I want to point out how difficult it is to get "clean" data using equipment this sensitive. Seemingly small things can throw some of the results off...which is why it's good to have guys with tons of experience running the show. For example, when we ran the first runs using a "known" wheel/tire combo (the Roval CLX64 with S-Works Turbo 22C), Cam immediately noticed that the positive yaw values seemed "off"...and it was traced to simply an end cap on the wheel fixture not being fully seated. Anyway, after 11 runs, here's how the data looked as a whole.

The big takeaway there is that the Roval CLX64 w/S-Works Turbo 22C truly is the "benchmark" for this grouping of wheels and tires tested. The Jet 6+, also with the S-Works Turbo 22C tire, basically matches it, although at the positive 15 deg point there appears to be an asymmetry (which should probably be investigated - Is it the wheel? Fixture? Tire?).

Looking closer at just the Jet 6+ runs, here's how they looked:

Another thing to note about the above data is that the Turbo Cotton 24C tire tested was my own personal tire with ~700 miles of front wheel use at that point.  As can be seen, the wider 24C tire gives up some drag, not only at zero yaw, but especially so at the higher yaw angles. However, don't forget that the Turbo Cotton tires have VERY good Crr properties, so when we look at this data in an "overall speed" context, the differences may not be as large. THAT analysis will be done in a later blog post.

Another wheel tested was my personal Zipp 101 wheel. For this one, I wanted to see the effects of tire width for such a shallow wheel, so the comparison was between the S-Works Turbo tires in both the 22C and 24C sizes. As you can see, the 2mm wider tires results in a fairly fixed offset across the range of yaw angles tested:

One of the things I wanted to check out in the wheel/tire testing was how well the venerable Specialized Trispoke/Hed H3 wheel performs vs. more modern, I wanted to see how well it worked with a VERY narrow tire, like it was designed around. As such, I took a brand new "out of print" Bontrager Aero TT 19C tire and compared it to the 20C Veloflex Record (that the wheel owner used as a tire) and also a 20C Continental Supersonic. As can be seen below, as compared to the Roval "benchmark", the older wheel leaves a bit to be desired, especially at yaw angles above 5 degrees. To be fair, this data doesn't include "power to rotate", which some claim can be a significant advantage for the Trispoke/H3. In any case, I think it's fair to say that of the tires tried, the 20C Continental Supersonic is probably the best combination of aerodynamics and Crr for that particular wheel.

Lastly, we looked at my personal Flo 90 front wheel, comparing the aero performance between a Continental Attack 22C, a Continental SuperSonic 23C, and an S-Works Turbo 22C tire. The surprising result there (for me, at least) was how well the SuperSonic tire performed out to 10 degrees of yaw as compared to the other slightly narrower tires. Combine that aero performance with the excellent Crr of that tire, and it looks to be a tough combo to beat as a front wheel application (I'll have more on the aero+Crr combos in a later blog post). It's also important to note how well the Roval CLX64 wheel performed vs. a wheel 26mm deeper!

That's about it for now for this blog post.  There's a ton of data I'd like to go through, and I figured it was high time I started sharing some of this stuff.  I wanted to throw this stuff out there first to generate discussion. I'll have more analysis later.

For those interested, the entire data set can be found in this spreadsheet here: Wheel Aero Data

Monday, September 7, 2015

Getting Caught Up...

Yeah...I's been about a year since I posted to this blog. Lots of "life" happening here.  Anyway, I recently had an unbelievable opportunity to "play" with Chris Yu and Cam Piper at the Specialized "Win Tunnel", and before getting into and (over?)analyzing the data from that adventure (we're talking wheel and tire combos, bare bikes, and even rider-on testing!), I thought it would be good to get my Crr spreadsheet up to date. I did test a few tires over the past year...not many...with the majority of what's been added being various flavors of Continental tires.

The spreadsheet linked to in the upper right corner of this blog page has had the following entries added:

Continental Supersonic 23C (New) = .0029, 27W for pair @ 40kph
Continental Attack 22C (~140 miles, "magic tire") = .0029, 27W for pair @ 40kph
Continental Force (used) = .0034, 32W for pair @ 40kph
Continental Attack 22C (ave. of 2 new) = .0036, 33W for pair @ 40kph
Continental Attack 22C (1 of 2 above, 118mi) = .0036, 33W for pair @ 40kph
Clement Strada LGG Gumwall 25C = .0045, 42W for pair @ 40kph
Kenda Kountach 25C = .0049, 45W for pair @ 40kph

So...a bit of discussion about those results above, especially in regards to the Attack models. As of now, I've tested a total of 4 Attack tires, with 3 of them being new and all of the new tires rolling ~the same at .0035-.0036. Even when taking one of those tires and putting ~120 miles on it, the Crr did not appear to change appreciably.  However, there was one Attack that was sent to me with what was claimed to have only ~140 miles on it...and that one rolled SIGNIFICANTLY faster at .0029. That's the one I call the "magic" tire. Knowing this, I would have to say that for anyone who wishes to run a Conti Attack as a TT/Tri tire, I would highly recommend roller testing the particular tire to make sure you have one of the lower Crr versions. For me, the majority of the Attack tires I've rolled have all been significantly slower. It might take quite a few tials...

The other interesting data point is the used Conti Force tire.  I had previously rolled another lightly used Force tire at .0029, as opposed to this particular one at .0034.  Again, like with the Attacks, it appears the Crr for these tires from Conti is highly variable.

The new 23C Continental Supersonic tested out at what I had previously estimated a new one would based on a well-used version I tested back in July of 2014, at .0029 vs. .0027. That ties it with the excellent Specialized S-Works Turbo Cotton 24C.

Well...that's about it for now.  The spreadsheet is updated with the tires I've tested in the past year.  Look for a couple of posts soon on my Specialized adventure!

Wednesday, October 29, 2014

An Oldie, but a Goodie...Field Testing Frame Differences with a Power Meter

I originally posted this back in 2008 on the forum and is an example of the types of equipment differences that can be determined with careful field testing.  Here's the link (click on the title below) to the full thread on's long but informative, and there's some pretty good "back and forth" with a few skeptics:

Something Borrowed...Something Fast!

So take this guy and his position:

...and put him on this guy's bike and adjust it so that they fit identical.

Then, let the first guy test both of these "back to back" using the same 404 wheelset with PT SL hub and cover....Any guesses on what the aerodynamic drag differences (if any) one would see?

Using RChung's most excellent methodology described here: Method to the madness

Here's the results for the P2K with the 404 wheels (the wheels on the P3C above):

And here's the results for the P3C:

So...what's the bottom line?

Well...taking the same rider, the same wheels, the same basebars and brake levers, and with the seat and extensions adjusted to deliver the same basically zero yaw conditions I apparently measured a drag difference of ~.023 m^2 of CxA (or Cda, whichever you prefer - .228 m^2 for the P2K and .205 for the P3C). Using Doc C's "rule of thumb", that basically equates to ~2.5s per km of time savings.

With only an extremely small amount of crosswind however (I could just barely detect it on my skin, not enough to even move leaves on trees), the drag on both setups drops significantly, with the P3C setup dropping more at .190 m^2 vs. the P2K's .220 m^2 for a growing difference of ~.03 m^2. That translates to a difference of ~3 seconds per km...or a full 2 minutes over 40K.

Can you imagine comparing the difference between a P3C (or even the P2K) against a frame that actually increases in CxA with increasing yaw, which is actually fairly common?

Sunday, September 7, 2014

New Zipp Tangentes - Speed, Course, and SLSpeed - the Crr results

A bit over a week ago, Zipp announced at Eurobike the release of their entirely new tire line; specifically, the Tangente Speed and Course clincher models (in 23C and 25C versions for both) along with the Tangente SLSpeed Tubular models (a 24C and a whopping 27C version).  Below you'll find my roller testing results for these new tires. The Speed models are based on a 220tpi nylon casing and forgo an under the tread puncture belt, while the Course models use a 127tpi nylon casing and use puncture belt.  The SLSpeed tubular models use a similar tread that is glued to a 320tpi cotton tubular casing with a latex tube inside and they also feature a puncture belt.

The previous Tangente models from Zipp were apparently very good from an aero standpoint.  From a rolling resistance standpoint however, they were "less than stellar"...especially in this day of tire companies understanding the value of low Crr tires and their effect on performance and "comfort".  So, one of the main drivers of this new tire development was in lowering the Crr of their tire offerings.  On this point, I'd have to say that they've succeeded, in that Course models are basically tied with the current "industry standard" Continental GP4000S 23C from a Crr standpoint, with the Speed models being slightly faster. Their new tubular models, the Tangente SLSpeed, are also very low rolling resistance, with the 24C model basically tied with the benchmark Schwalbe IronMan Tubular, and the 27C (with the helping of its extra wide casing) taking over the current top spot for a "brand new" tire on the overall list of tires I've tested.

So, here's the nitty-gritty data for these tires, including data for the Schwalbe IM tubular, my "benchmark" GP4000S 23C tire, and the old model Tangente tubular.  All of the clincher data for this round was performed on a Zipp Super 9 clincher disc, with the tubulars all tested on Zipp 900 tubular discs for consistency. In rank order from lowest Crr to highest:

Zipp Tangente SLSpeed 27C Tubular = .0028,  26W for pair @ 40kph, width = 26.8mm
Zipp Tangente Speed 25C Clincher = .0030,  28W for pair @ 40kph, width = 24.8mm
Zipp Tangente SLSpeed 24C Tubular = .0032,  29W for pair @ 40kph, width = 23.5mm
Schwalbe IronMan Tubular 22C = .0032,  30W for pair @ 40kph, width = 21.7mm
Zipp Tangente Speed 23C Clincher = .0033,  31W for pair @ 40kph, width = 23.8mm
Continental GP4000S 23C = .0034,  32W for pair @ 40kph, width = 24.8mm
Zipp Tangente Course 25C Clincher = .0035,  32W for pair @ 40kph, width = 24.7mm
Zipp Tangente Course 23C Clincher = .0035,  33W for pair @ 40kph, width = 23.8mm
Old Zipp Tangente 23C Tubular = .0045,  41W for pair @ 40kph, width = 22.4mm

So...what are the takeaways here?  Well, I think it's fair to say that Zipp accomplished their goal of significantly improving the Crr of their tires, which can be easily seen by the comparison to the old Tangente tubular. Even the slowest of the new tires would save ~7W for a pair at 40kph, with the faster tires requiring more than 10W less at 40kph.  That's significant.  Also, in comparison to the GP4000S, the 25C Course model is basically tied with it, both in Crr and in actual tire width (at ~24.7mm) with the 23C Course model being only slightly slower (within the error margin of the testing).  The 23C version of the Speed models tested out slightly faster than the GP4000S (again within the margin of error) but measures a full 1mm narrower when mounted on the same rim.  That should help its aero properties. The 25C Speed model, however, is significantly lower Crr than the GP4000S saving a predicted 4W for a pair at 40kph, while measuring out at the identical width.

On the tubular front, the new 24C Tangente SLSpeed tire rolls just slightly better (within .0001 Crr) of the Schwalbe IronMan tubular, which is not surprising considering their similar construction (tread glued to a 320tpi cotton casing).  The 27C Tangente SLSpeed tire rolls VERY fast, but its extra wide 26.8mm mounted width is going to result in an aero hit.  I'd call that one a "rear use only"...but only as long as it can be shown that the width doesn't "give back" aerodynamically the gains that are made in Crr.

Well, that's the Crr results. What remains to be seen is how these tires perform aerodynamically.  But, as I've said before, and we've seen recently with tires like the Specialized Turbo Cotton, low Crr can "make up for a lot of aerodynamic sins".