We’re continuing on our quest to evaluate a slew of 650c-sized equipment. Today’s episode covers Zipp’s 404 650c Firecrest Carbon Clincher. We took a brief look at the wheels when they debuted in February of this year - HERE. You can also find a two-part in-depth piece on our 650c Serotta Project Bike (the bike that we used to test these wheels), linked at the bottom of this page.

When we first learned of this new mini-size 404, Zipp claimed that it packed all of the technology of the larger wheel. It has the same rim shape, same hubs, same spokes, and the same special high-temperature resin to safely deal with brake heat. We later learned that the 650c wheel even carries a potential aerodynamic advantage over the 700c wheel, which we will detail later in this article.

At first glance, the wheels look as we expected: B-E-A-utiful.

Our test pair of wheels shipped with the same accessory kit that consumers receive. Each wheel includes:

-One stainless steel quick release skewer (front/rear specific)
-One 650x20mm rim strip
-One 650c Zipp Tangente butyl inner tube
-One removable core valve extender
-Two valve extender wrenches
-One pair of Tangente Platinum Pro EVO brake pads
-Instruction manual
-1.8mm 11-speed spacer (rear wheel only)

Zipp gets a big-ol’ pat on the back for including inner tubes. I don’t know of anyone else that does that. Zipp got a ton of grief in the past for not even giving you quick release skewers with their wheels (and the grief was well-deserved). It looks like they’ve listened to customer feedback and now give you a whole bag of tricks with your wheels.

The first thing I noticed about the rim is that – finally – the 650c Zipp wheels have their trademark dimples.

According to Zipp, the internal rim width is 16mm (ETRTO 16-571). This is much wider than their 13mm aluminum hybrid wheels (such as the older 404 650c clincher), but narrower than some competitors’ 17mm+ internal widths.

It seems to me that Zipp has taken a slightly different approach than some competitors. We have a few that have stayed narrow, such as Madfiber, Campagnolo, and DT Swiss. We have some that are slowly going wide, such as Shimano, Reynolds, and Enve. Then there are those that appear to be making their new product as wide as possible (internal and external), such as Hed.

My opinion is that Zipp is taking a calculated and moderate approach. They are committing to wide rims for all of their carbon clinchers, but they’re only going so wide. All of the competing rims with 17mm internal widths are technically too wide to use a 23mm tire, per the ETRTO set of standards.

Are the standards outdated; not taking into account modern tire technology and stronger carbon/Kevlar beads? Perhaps. It appears that many people are using 23mm tires successfully on 17c rims. Because there isn’t an official ruling on a ‘16c’ rim such as Zipp’s Firecrest line (the ETRTO standards only cover odd numbers), we’re able to assume that a 23mm tire is safe-and-sound – or at least more so than a 17c rim.

Zipp couples their moderate internal width with a slightly angled braking surface and moderate external width. At the center of the brake track, the 404 650c Firecrest Carbon Clincher measures 24.7mm. Maximum width at the broadest point of the rim is 26.5mm.

The widest point on the rim is nearly 2mm wider than the braking surface, and is located quite close to the spokes. The shape is literally in the opposite orientation of old V-shaped rims. Call it a fat-bottomed U-shape rim. Can I trademark that?

Given the internal and external rim width of the Firecrest line, Zipp recommends 23mm tires for most users. You can use whatever width you want, but they say that 23mm hits the sweet spot of aerodynamic and rolling performance.

Zipp has had many behind-the-scenes revisions of their 88/188 hub set, but the basics remain the same: adjustable bearings, snap-on spoke covers, and 17mm axles:

The rear 188 hub features an 11-speed Shimano-compatible freehub for 2013. The wheels include a 1.8mm spacer for use with 9 and 10-speed SRAM and Shimano cassettes.

Hubs are one place that I’m eager to see some changes. I think Zipp has a very good racing hub. It is light, minimal, and has low bearing drag. It does everything a racing product should do – which is maximize speed at the expense of longevity.

I’ve learned over time that most triathletes actually want the appearance of speed, but without the reality of actually dealing with and paying for the required maintenance of real racing products (sorry – it’s true). With this same model of hub on other wheels I’ve ridden, I usually re-adjust the bearing preload every 2-3 months, and replace the bearings every 6 months (weather dependent). I’d love to see Zipp go to a 15mm axle, non-adjustable preload, and large angular contact bearings. I think a simple and durable design wins with 99.9% of customers, and would likely only cost half a watt of bearing resistance.

Aero Performance

While on the phone with Zipp Technical PR Manager, Dave Ripley, I asked about the performance of this wheel in the wind tunnel. Back when I was just getting into the sport, there was a hot debate as to whether 650c or 700c wheels were faster. Proponents of 650c said that the smaller surface area meant that they were faster. There’s less wheel for the wind to see. As a bonus, their lighter weight improved acceleration. Proponents of 700c said that they have the advantage of turning fewer revolutions for a given ride distance, so the spokes encounter the air less often (reducing drag). Also, their heavier weight means that they hold momentum better.

Who is right? The bickering has seemed to die down in the past several years, so I’m here to start it back up – and add some data in to the mix.

Zipp Technical Director, Josh Poertner, provided a graph and some information for us.

“The new San Diego [Wind Tunnel] data sheet format doesn’t import directly into our internal database yet… so pardon the Excel graph. Here is a direct comparison of 700c 404FC carbon clincher overlaid onto the 650c test we did comparing Firecrest to the 404 [aluminum] hybrid clincher. These 3 tests were all done within a few hours of each other on the same day. Tires are [Continental] GP4000 on the 650 and GP4000 S on the 700c. Tires are a potential bit issue as we see differences between same model of tires due to different molds… so, for instance we buy specific GP4000 S tires from the identical mold for tunnel testing, and even then keep them marked ‘A’, ‘F’ etc. We can see ~10 grams difference between tires from same mold and as much as 20 between different molds of same model… so we’ve tried to keep them as close as possible, but at the small differences between 700 and 650, it’s hard to say what’s tire and what’s wheel.

Per data point, the difference is as low as 8 grams at 17.5 and as much as 20 grams at 5, but averages 12 grams delta. At this velocity, 9 grams is 1 watt of power. Ultimately it looks like the [rolling resistance] data will sway this one way or another. I’ve never seen any 650 vs 700 data for same tires, but am interested to see if it’s a real difference or more just theoretical similar to the wider tire bead seat, which calculates out to be lower Crr, but has proven immeasurable every single time we’ve tried it.”

On the graph below, the red line is a 700c 404 Firecrest Carbon Clincher, the blue line is the older 650c 404 aluminum hybrid clincher, and the pink line is the new 650c Firecrest Carbon Clincher.

Because the graph is so small, I’ll zoom in on the ‘meat’ of it – about 7.5 to 17.5 degrees:

Just eyeballing it, I see about a 15 gram delta at 12.5 degrees of yaw between the 650c and 700c Firecrest 404s. According to Poertner, that’s about 1.5 watts, assuming we’re controlling perfectly for variation in tire manufacturing.

The big take-home for me is this: We can confidently say that – if nothing else – 650c wheels are NOT inherently slower than 700c. If anything, they are slightly faster. The reason I point this out is that there are still some people out there who simply assume that 650c wheels are “slow”. They’re different, so they’re bad. They’re just stupid. Who would want them? Ahem! Not ten years ago they were the norm, and there are still far more female Kona champions who have ridden 650c (or smaller) wheels than 700c wheels. They’re not slow, and I’m throwing that argument right out the window.

Editor’s Note: Yes, someone is going to point out that nobody makes a 650c size clincher latex inner tube yet. We know that. We’re talking about wheels (not inner tubes) at the moment, and believe that it’s only a matter of time until someone makes your beloved latex tube.

Ride Impressions

Data aside, how do the wheels ride? I’ve ridden quite a few miles on the 700c version of this wheel, and can only say that the 650c is similar… but better. They’re lighter than their 700c counterparts, laterally stiffer (due to the smaller size, equal number of spokes, and identical flange spacing), and less influenced by crosswind.

It’s the crosswind handling that I really notice and enjoy. This is also an area that makes me even more confused when I see smaller ladies wanting to ride 700c wheels. Proper fit and handlebar drop aside, the small 650c front wheel is noticeably easier to handle when the wind whips up. This also makes me really want a 650c version of the 808 Firecrest… why not have the aerodynamic benefits of the deep rim, plus the handling benefits of a smaller diameter? If Zipp truly wants to capture the 650c market, I think they will have to take that step.

When coupled with Zipp’s Tangente brake pads and Dura Ace 9000 levers/calipers, the braking performance of the 650c 404s is outstanding. This is also one area that can be hugely affected by weather, so I should mention that I only had the opportunity to ride the wheels on warm days (i.e. 70-80 degrees Fahrenheit), and with dry to light rain conditions. We recently tested a pair of Profile-Design carbon clinchers that had wonderful braking ability in warm weather, but very poor braking with cold temperatures and pouring rain. At this time, I cannot make any general statements about all carbon clinchers’ braking performance in cold/rainy weather. Fortunately or unfortunately, we can’t test every product in every possible weather condition.

At $2,725 per pair, the 404 650c Carbon Clinchers don’t come cheap. I think Zipp is offering a lot of product for your dollar, and I’m not one to harp on price in general. If you have that much cash burning a hole in your pocket, this is not a bad way to spend it. If you can't afford them, there are cheaper (and fast) options out there, such as Hed's $1,900 Jet 6, and the ever-present used market.

Michelin Pro 4 650c tires

We needed some tires for our 650c wheels, and Michelin sent along a pair of their Pro 4 clinchers:

We installed these, along with Zipp’s butyl inner tubes and valve extenders. At 100psi, the tires measured exactly 23.0mm wide when new.

It is worth noting that the maximum tire pressure of the tires and rims are not equal (which is not uncommon). The tires top out at 116psi (8 bar), and the rims can handle 125psi (8.62 bar). You MUST treat the lowest number as the true ‘max’ of the combination.

I pick tire pressure conservatively with carbon clinchers, to allow for heat (and tire pressure) build-up. 100psi was the magic number for my test rides, and seemed to work just fine. Carbon clincher wheels also make me wary of running a too-low pressure, because I don’t want to risk striking the rim on a pothole.

I consider the Michelin Pro 4 to be one of my top 650c tire choices. Historically, Michelin makes a product that is very puncture resistant, and towards the faster end of the rolling resistance curve. Installation difficulty is often at the mercy of your rim. I tried to install these on an older 650c aluminum hybrid 404 clincher wheel and literally was unable to mount the second bead. It was so tight that I was going to break something if I kept trying (snap the tire bead, break the rim, etc). However, on the 404 Firecrest Carbon Clincher, the tires mounted with ease due to the deep rim channel.

Similar to my desire with most other 650c tire manufacturers, I’d love to see a true 25mm option in the Pro4. It’s a great choice for training, and with today’s wide rim shapes, is a viable option for racing.