Meaningful Differentiation

The one convention we have left to cover following last week's wind tunnel test is the "how many seconds will I save or spend in the mythical 40k TT by making any of the above choices?" Since the results so clearly deserve a different take on it than what's been presented in the past, we're going to express it in terms of distance rather than time. 

Our last wind tunnel trip really has the big guys sweatingUsing a 303 instead of a Kinlin XR31T/FSW3 or an AForce Al33/RFSW3 will put you 40mm (we originally said .4mm - Mike carried the 2 wrong somewhere earlier, and an eagle-eyed commenter caught it) ahead after 40k. The construct here is that the 303 is ridden at a power that makes the rider go 25 mph, and the others ride at that same power. The FLO30 and HED Belgium+ are a couple of bike lengths behind. That's it, and that's the extent of our summary report there.  

Maybe we just magically picked the 5 wheels where this would occur? Maybe our distribution (which again, is something of a distribution of distributions) is a bit off? We can't help but concluding that if you choose any good, modern wheel of some moderate depth and width, you're putting yourself at no aerodynamic disadvantage with the (possible) exception of in high level TT competition. 

There are some other differentiators, though. One is rolling resistance. Your rims don't make any real difference there, but your tubes might. And latex tubes have been shown (note that I didn't use the word "proven" since some of you are already screaming "but that's not a real world test!!!!") to have lower rolling resistance than butyl tubes, and the delta is bigger than the aero gap seen in our test. And rolling resistance doesn't decrease when you draft. If you use butyl tubes, there's a range of rolling resistance there, too (same link as above).

Tires make a difference too. Much bigger than wheel aerodynamics. Just yesterday, I read some guy on a forum that he could clearly feel the difference when he switched to his carbon clinchers versus his other wheels that have Gatorskins on them. He didn't say what tires were on his carbon clinchers, but it's not at all unlikely that there was a 20w difference in the tires he's using - so OF COURSE he can feel it. And this is likely to be the "noise" in the usual anecdotal comments like this. Our guess is that people had always put the garden hose tires on the alloy training wheels, with fast tires on the carbon race wheels. Now that people are sharing great info on rolling resistance and people are paying more attention to it, it's likely that the tires were making the difference, yet people blamed it on the wheels. Isolate your variables.

So, within wheels, what does make a difference?

Looks make a difference. I mean let's face it, carbon looks pretty freaking cool. If carbon happened to be really ugly, would people use it? If you dig deeper or shallower wheels, that's going to make a difference to you. We've plainly stated before and will plainly state again right now that getting a Special Edition matte finish on our XR31Ts exponentially increased our enthusiasm for what was otherwise already an easy rim to love. And then there's the whole "ceramic coated Al33s sold out in 4 days" thing. So go with it, and don't feel guilty about it.

If Victoria's Secret had a wheels catalog...Price makes a difference. You could pay for an entire season of race or gran fondo/century entry fees (with enough left over to buy fresh tires all year long) with the price gap between FSW3s and 303s. Having money left over to not think twice about saying yes to an event you want to do makes a difference. You can put a Powertap into a set of RFSW3s and still save most of a grand from a lot of carbons. Training with power helps you make a difference. 

Handling makes a difference. Not getting blown around in crosswinds makes a big difference. Tire set up and cornering makes a big difference (never forget that the impetus behind the Rail series was width more than anything else). Having a front wheel that holds a line makes a difference.

Weight makes a difference. I'll get skewered for saying that, but "light and stiff" are the two most popular answers when we ask people what they're looking for in a set of wheels. They often exist on competing curves, so getting the right mix of both is a compromise, but we're able to do it with PLENTY of builds. 

Hubs make a big difference. We've said it for years and years - buy hubs first. You won't roll any faster out of the box with fancy hubs, but good hubs will see you through several sets of rims - rims are a wear item, hubs don't have to be. 

And finally, build quality makes a huge difference. When you install your wheels they should be silent, round, and true, with nice even tension on the spokes. And they should stay that way for a good long time. If the builder has spent some effort helping you discover what mix of components will work best for your use, you should be able to ride them for a long long time without doing much more than keeping them clean (WITHOUT using a pressure washer!!). 

Good thing I wore my kevlar underoos today because I have a feeling we'll take some heat for such heresy. 

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Mike – ThanksJoe – We're not doing a direct measured test as there isn't any reason to do so. German Tour Magazin identifies a 3 watt gap between current FC303 and FC404 in their issue #8 from 2016. Zipp also identifies a 3 watt gap between FC 404 and pre-FC 303 in this flyer – We've posted both in relation to this topic. Hopefully those do it for you, because they close the issue for us.


30mph = 44fps. 9 seconds at 30 mph cover 396 feet.304.8 mm in a foot.The difference in those benchmark rims is 120,700.8 mm.Yes, the difference between those rims at 25 mph will be less than 120,700 mm. Perhaps it is even a meaningful differentiation. Now I too, have a handle on the difference between the two benchmark rim depths. I appreciate the info.Thanks for the links.


We aren't belligerent or defensive. Neither do I think you're the only one who's curious as to how the 404 or the 52 compares to what we build now, I just think other people feel they've been given a good handle on that, and we agree. At 30mph, the difference between a 404 and 303/FSW3/RFSW3 is 9 seconds over 40k, correct. At lower speeds, of course, the wattage differential to equalize speed declines. To my point that we think we've given a good handle on these differences, that conversion was given in bold italics in the previous linked post.


DaveIt's not that I agree or disagree with your methodology.I just wanted to find out how the Rail 52, a product you developed and subsequently discontinued for various well documented reasons, compares to the products that replaced it. The Rail is a product that November most likely has the most knowledge on its Aerodynamic properties. Given the time and effort to obtain that knowledge, I, for one (and apparently the only one), was curious how the current product line compares to your previous offering. That is all. You had a product. You discontinued a product. You offer a new product. I would like to know how your new product compares to the old product.It seems that you get very defensive when this topic comes up almost to the point of belligerence.I have bought multiple sets of wheel from you in the past and even tested a set of RFSWC 60s years ago and have been consistently pleased. (Although those 60s where a little too much wheel for me) I really had no intention of setting you off. Oh and it's 9 seconds.


Hi Joe,Zipp collateral was discussed as recently as this post, which also spells out very clearly how a 3 watt difference is accounted for in the mythical 40K TT. The Tour Mag test was most recently discussed in You have to pay to download that one, which is worth doing. I know I've also discussed them in other posts and in various forum posts and other venues, but I don't catalog references like that so those two links will have to do. For the test we just did, we proposed the 303 as the most relevant benchmark. You can, and it seems like you do, feel differently. That's fine. We've given what we feel is a very clear array of information about the topic. Again, it seems like you disagree with it. That's fine. If you'd like to take a 52 or a 404 to the tunnel and test for yourself, we'd loan you the rims to do it. But for us the issue has been addressed and closed, and we're not going to address it any further. We've done our job.ThanksDave


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