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FEATURED BUILD - FSW3 with PowerTap.

Our last trip to the wind tunnel proved that the Kinlin rims in our FSW3 wheels are every bit as fast as those 40+mm carbons you use on race day. So now that your everyday alloys can also be your game day wheels, there's no better time to add a PowerTap. Especially since we've added tires (installed) and knocked $135 off the price.

 

 

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Friday
Feb102017

Wind Tunnel Testing the Al33, XR31T(FSW3), and others, Part 2

Yesterday's was a quick post to show the basic results. Today's post will explain the Angle of Attack distribution that we've used, and fill in some of the finer details on the test. 

The test occurred at A2 Wind Tunnel in North Carolina. A2, along with the San Diego Low Speed Wind Tunnel, is one of the two default standard, publicly accessible wind tunnels in the US. If you want credible aerodynamics data, A2 is a an outsanding place to get it. No one from November was at A2, we Skyped in during the test. The test is a very standard one - 30mph test wind speed, temperature and pressure are normalized. We used a 23c sized (Continental's chosen descriptor) Continental GP4000sII tire, inflated to the wind tunnel standard 100psi. The alloy wheels used a tube with a 48mm valve stem while the Zipp used a 60mm valve stem, so valve stem protrusion was normalized as closely as possible. Other details of the builds have been detailed before

The standard test sweep is to go from 0* to 20* angle of attack, or yaw angle, in 2.5* increments. This is enough resolution to give an accurate representation of how the wheels perform through any statistically significant wind situation you will encounter. Wheels were tested alone, front wheel only. There are already some rattles of "this is irrelevant because it doesn't account for frame and fork" pushback on this. Simply, testing wheels standalone has decisively proven to have outstanding transfer to their performance in a bike system, and it's impossible to test with the range of bikes/forks/situations to satisfy everyone. The validity of this test's scope is established legislation, which you are free to relitigate as you wish, but it's not something we'll engage in arguing. 

Al33 in the tunnel at A2

Wind speed is 30mph. This is the standard test speed as it's been established to give the cleanest data. You can scale with software to produce results for more or less air speed, but the shape of the curves doesn't change - a wheel that's a laggard at 30mph doesn't become a star at 20, it stays a laggard. But since the effects of air resistance increase so quickly with air speed, the differences between wheels get compressed at lower air speeds.If you want to do the quick and dirty calculations on watts versus grams of drag versus time in the mythical 40k TT, here's the teacher's edition: using the 30mph parameter, 10g of drag roughly equals 1 watt, and 1 watt roughly equals 3 seconds in the mythical 40k. Not good enough for real science, but good enough to become a hyper-aware wheel consumer. 

Something we included in yesterday's chart that we've previously omitted are the blue bars showing the amount of time you're likely to spend encountering any given wind angle. How we arrived at this distribution needs explaining.

It had been an established convention that 10* was THE heavyweight angle, likely because Zipp's collateral always placed such heavy importance on 10* in particular, and the 10* to 20* range in general. When they give a time savings figure, it is computed at 10* as the only angle. However, the world has long since moved past "because I said so" as an acceptable premise, and Trek and Flo have both gone to the trouble of doing actual data collection in real world situations, and come up with distributions that show that lower angles are actually vastly more prevalent. In fact 10* is shown to be largely irrelevant.

We've linked a few hours of quality technical reading there, but the abstract is this: at real world riding speeds and in real world conditions, this is what you see. The Flo data is very plainly presented in percentages, and you'll notice that if you add the percentages up they don't equal 100% - that's because 0 to 20* doesn't encompass every situation encountered. You have a bunch of small data points going out from >20*. The Trek data is harder to break down, but break it down we did. 

The frequencies we show are a straight average of those three data sets - Flo's gathered data, Trek's data from the Ironman AZ course, and Trek's data from the quite windy Ironman Hawaii course. Anyone can argue with our methodology on this, but we think that this is the most robust, relevant, defensible distribution available. And for what it's worth, Hawaii distributed a bit differently, being very exposed and windy, but the Flo and Arizona data matched very well, and Hawaii really wasn't that different.

We are not asking you to believe anything on faith. Every bit of what's been done and how it's been done are available to you here and in the links. As none of these rims is our own or available exclusively through us, we derive no benefit from the data leaning one way or another, or shading the data in any way. This entire exercise to to provide the wheel market with good information to become educated about wheel aerodyamics. 

More in subsequent posts, but I've run long as is, so that's it for now. 

Thursday
Feb092017

Wind Tunnel Testing the Al33, XR31T(FSW3), and other alloys

This blog, and series, will be a way more difficult story to tell than I'd thought it would be. 

What we'd expected was that the Zipp 303 reference wheel would be that shade faster at the heavily prevalent and thus more important narrow angles of attack (aka yaw angles), and then extend that lead out into the angles that occur with much less frequency. What actually happened was that the Al33 (our RFSW3 wheelset's rim) and the Kinlin XR31T (that we use in the FSW3) both performed better than the 303 at the most prevalent low yaw angles, starting to cede a bit at around 7.5* and going on from there.

 

When you do a test like this, you get a lot of data, and it takes a while to chew and digest it. What we present here is just a first, very broad, pass at things. 

The blue vertical bars that you see in the graph are the amount of time the average cyclist is likely to spend encountering each wind angle during a ride. We will offer a very complete explanation of that in the next blog. 

For now, we're just trying to wrap our heads around this, and make good on all the teasing that we've done. Sorry for that, hope it was worth it. 

Enjoy

Wednesday
Feb082017

BYO Hubs in RFSW3

The particularly eagle-eyed among you may have noticed two "I'll send you my hubs" options in the hub pulldown options for RFSW3 builds. That's right, you can send us your hubs and we'll build them into a set of RFSW3s for you.

Some of Dave's cache of "I can't throw that out, no way!" stuff

A lot of you are probably like us, with a stash of stuff that seems too good and too useful to get rid of, but somehow you never get around to actually putting any of it to good use. Maybe you've got a set of wheels where the rims are worn out or dented or you crashed them or spokes started braking or whatever. Maybe the rims failed prematurely but the hubs still have plenty of life. You might have a set of wheels that came with your bike but they've got kind of crappy rims and spokes so you never used them. We've had a bunch of people contact us with these very situations, and we're very happy to help.

It does require some extra work for us, in that we have to manage incoming packages, assess the hubs (if we think you're better off not reusing them, we'll tell you), clean them up, measure them, blah blah blah, so we can't make it a bonanza of cost savings, but if you've got a set of hubs that's in good shape it's definitely worth doing. We've differentiated the price on straight pull hubs a bit because they're harder to measure and work with, but we expect there are a lot of LOT of almost-never-used take off wheel sets hanging in garages and basements and sheds that are perfect candidates for this. 

We're also building out a partial build service in the Custom section where you can add different components a la carte and have us assemble them for you. And yes, we'll be offering Al33 rims for sale as stand alone rims, we just haven't yet heard what if any MAP policies or whatever there will be, so we can't post that yet. 

It's sort of funny how excited I am about tomorrow's test. I am truly a geek. 

Monday
Feb062017

Aerodynamics thoughts

This week, the Al33 and a number of other rims will be tested in the A2 wind tunnel in North Carolina. We aren't paying for it, it isn't our test, but we agitated for it to happen, facilitated all of the arrangements, and designed the test. Without those inputs from us, the test wouldn't have happened. Call our stake sweat equity. We won't be there, but the US distributor will be, and we will be there in virtual.

I'm excited. I love testing, I love the wind tunnel, and I've learned a lot every time we've done it.  

The test will use a 2017 model Zipp Firecrest 303 as a baseline. Tested wheels will be a HED Belgium+, a Kinlin XR31T, the Al33, and a Flo30. All wheels are 20h rims built with CX Rays and standardized hubs, except for the 303 which is of course an 18h wheel which uses Zipp's own hub and CX Sprint spokes. 

The test will be done as a wheel only test. This has plusses and minuses, but it's proven to be an accurate way to test wheels and it allows wheels to be tested in a time efficient manner, which means we can include more wheels.

Test tire will be a Continental GP4000sII in 23c size. There will also be a 25c GP4000 there, how much testing gets done with it depends on time available.

All the quantitative data on each rim/wheel will be presented - depth, weight, inner and outer width, and retail price. 

We'll be doing the standard 20* sweep in 2.5* increments, on one side. Since these are all symmetrical front wheels, doing both sides would take time that would reduce the number of wheels we could test. We will also include steering axis force data as provided by A2. 

Not entirely certain how the data will be presented. My inclination is to show the standard graph like you've all seen 100 times, and then overlay some of the more defensible angle of attack distributions over top of those. It makes the most sense to then use those distributions to create a one number score for each wheel. 

I'd encourage anyone who wants to get the most from this information to become as informed as possible about the benefits and limitations of aerodynamics testing. Tour Magazin is an amazing resource, and you can go to the App Store, download their app, and buy issues for about $3 each. Issue 8 from 2016 is particularly good. Become familiar with the other methods like Chung and Alphamantis. 

A few bullet point thoughts:

1. Any quantitative test will have some strengths and weaknesses, but no wheel can make aerodynamics claims without credible quanification that allows at least some comparison to relevant standards. It shocks me how many brands still try to skirt past with a "trust us, we're fast!" line of bull. If the whole sales proposition for any wheel is that it's fast, yet it shows no data, I think you know what I'd say to that. This principle is why we insisted that the Al33 absolutely needed to be tested. 

2. Depth and speed are not interlocked. We first showed this four years ago when doing the original Rail 52 test, where the 52 proved faster than even the 85mm wheel than we'd been using, and was faster than the deeper Zipp 404 at angles from 0 through 5 degrees. 

3. We're still using the GP4000 in 23c size because that's been the standard, and it's still a VERY widely used tire in situations where aerodynamics are important. Our previous tests showed a reliable pattern that wider tires had a linear and predictable negative effect on outright aerodynamics. 

4. The Zipp 303 gets used "as is" because it's a wheel system, and its value as a baseline is in using it as it's been used in other tests. That allows you to make worthwhile comparisons to the greater universe of what's out there.

5. Have reasonable expectations. In the Tour Magazin test I referenced earlier (seriously, download it), the difference between best and worst was 13 watts. That's 40ish seconds in a 40k TT at 30mph between a Mavic Ksyrium and a 404 and DT Swiss 65, which were the fastest wheels in the test. That's about .4mph, worst to first. Anyone telling you you're going to go 2 or even 1mph faster by just switching to more aero wheels is selling you a load of crap. 

Okay, that's it for now. Looking forward to Thursday. 

 

Wednesday
Feb012017

Dave's road tubeless doubts

This post deserves a TL:DR summary, which is: If you aren't super comfortable with road tubeless and willing to spend some time and expense figuring out exactly which combo works for you, and also willing to petentially suffer a reduction in the lifespan of your wheels, stick to tubes. With a whole bunch of data now showing superior rolling resistance with clinchers and latex tubes, that may be the best way to go in any case. The ability to use latex tubes is another bonus of aluminum rims. 

For mountain bikes, tubeless is mandatory. For cross, it has its challenges (which we've done a heck of a lot to help eliminate) but the benefits can be so profound that the juice is for sure worth the squeeze. For road, though Mike and I personally use tubeless, we haven't been evangelical. It comes with downsides, which we'll talk about here. 

A potential "do as I say and not as I do" instance

We've been observing and talking about spoke tension drop in clinchers for a couple of years now. Since I've done THE WORST job at tagging posts, it's hard to find all the posts on the topic, but these two posts from last spring are good examples. There were a bunch of forum discussions in the spring of 2014, but I can't even recall which forum they were on. We even made a video to show the effect last spring. 

Wheel Fanatyk has what might be the second best wheel blog out there, and they did a series of posts in the fall about this whole topic, including the outward splaying of brake tracks which we'd discussed in above-linked post called "Pressure Drop Follow Up." What they did in particular, for which I have huge appreciation, is measure a bunch of tires to find how tightly they will fit. Their whole methodology and execution of this is excellent. What their measurements reveal is something that anyone who's installed more than one kind of tire will already have known - tire bead circumference varies by manufacturer and model. 

They've also measured overall circumference of a number of different rims, but they haven't shown the more relevant tire trough and bead seat diameters (which are simple secondary measurements from what they've done and shown). The overall circumference is of little value in its own right as, for example, a Zipp 404 shows a large outer diameter, but 404s are known to be relatively easy to fit tires onto (perhaps too easy?).

In order to resist the higher inflation pressures of road tires, road tubeless tires need a tight fitting carbon bead. The carbon bead more or less doesn't stretch, which is critical to having the tire not blow off the rim, and thus to keeping your teeth in your head. In that respect, it works quite well, but at what cost?

Non-tubeless road tires have either wire or Kevlar beads (if you're reading this, you probably have Kevlar beads). You probably notice that your tires get easier to install over time, which is because the beads stretch a bit over time. This stretch reduces the constricting pressure that the tire imparts on the wheel. 

Compressive tire loads cause a reduction in the circumference of the rim. Wheel Fanatyk estimates a possible 1mm reduction in the circumference, and my calculation gave me an estimate of .1mm in diameter reduction, so they estimate a bigger effect but we're not that far off in the absolute. I based mine off of "the spoke tension drop is x, the thread pitch of a nipple is y, the spoke tension drop is equal to z turns of the nipple, therefore the diameter reduction must be..." The important thing is that we're both seeing the same effect, in the same direction, with reasonably similar magnitudes. 

Compression is bad for the wheel for several reasons. It takes more initial spoke tension to maintain the minimum necessary functional spoke tension. Compression changes the dish of a wheel. Compression puts stress on the rim that almost certainly shortens a rim's useful life span. 

At the risk of speaking against my book somewhat here, I have two road bikes in current use (one disc, one rim brake, otherwise more or less identical) and those four tires are all tubeless. It works fine for me, but on a scale of 1 to 10 in tubeless experience, I'm about a 643. So if you are willing to invest time and money into getting your road tubeless set up perfectly, knowing that it comes with the potential to compromise your wheels, then it may be worth it to you. Otherwise, tubes are your best bet.