64 VELO SEPTEMBER 2014 VELONEWS.COM

Carbon clinchers used to turn heads for all the wrong reasons. Now, they’re ready for prime time

TECH & TRAINING » CARBON CLINCHER TEST

The latest generation of carbon clinchers has improvements you can unquestionably see and feel. Wider rims improve cross-wind stability and corning. Improved carbon resins and brake tracks dramatically improve braking performance. Compared to yesteryear’s carbon clinchers, there are no marginal gains here, these are gains in leaps and bounds.

By Logan VonBokel and Caley Fretz

Photography by Brad Kaminski

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65

OVERALL SCORE 100 POINTS

SCIENTIFIC TESTING 35 PTS

RIDE QUALITY 45 PTS

VALUE 20 PTS BONTRAGER D3 72

ENVE

3.4

82

ZIPP 3

03 88

URSUS 73

REYNOLDS 46 74VISION 74

XENTIS SQUAD 4.2 81

14 17

15 16

1818

21

35

33

30

2937

17 16

23

35

27

29

21 36

2432

3933

MAVIC CC40 71

RIDE QUALITY 45 POINTS

ACCELERATION 15 PTS

CROSSWINDS 15 PTS

BRAKING 15 PTS

XENTIS SQUAD 4.2 30

ENVE

3.4

37

ZIPP 3

03 39

MAVIC CC40

33

REYNOLDS 46 35VISION 35

BONTRAGER D3 36

12 14

9 12

910

12

13

14

13

1114

10

13

13

9

1112

11 10

912

138

URSUS 29

The road to successful carbon clinchers has been rocky, full of cracks and crevices, and an unacceptable number of outright

failures. The industry spent years taking a step forward, then two back, and has been rightfully accused of bringing new technology to market too quickly, of selling wheels at exorbitant prices that were not ready for prime time to unwitting consumers.

Our skepticism of the technology is born of personal experience. Three years ago, Velo brought a carbon clincher to failure during ride testing. Under hard braking by a heavy rider on an exceptionally steep descent, heat buildup soft-ened the brake track and increased pressure in the tire to the point of catastrophe. The rim walls bowed outwards; the tire blew off. Both were de-stroyed. The rider careened toward a guardrail at 20 miles per hour, his rear wheel fishtailing wildly. He stayed upright, but only just.

But that was then, and this is now. Today, car-bon clinchers are ready for the big show. Thanks to new resin technologies and a clearer under-standing of the stresses placed upon a clincher rim under hard braking, today’s carbon clincher wheels are a legitimate option. They are lighter, more aerodynamic, and, yes, safe under any-thing but extreme riding conditions. They pro-vide many of the advantages of carbon fiber race wheels without the hassle of gluing tubulars.

This year, across hundreds of hours of testing and eight different wheelsets, the biggest issue we encountered was a sticky freehub body.

The eight wheels tested and reviewed on the following pages have rim depths between 35mm and 50mm — the sort of medium-profile wheel that riders might use every day — because that’s what these are, after all. Everyday wheels. Very expensive everyday wheels.

Each was subjected to extensive on-road test-ing as well as wind tunnel testing at the A2 Wind Tunnel in North Carolina. The final results are a combination of quantitative and qualitative as-sessment. Though numbers don’t lie, attributes that can only be measured on the road, like brake performance and stability in crosswinds, are equally important.

For the cost, which is unquestionably high, carbon clinchers need to perform every day, in all conditions. They must be fast enough for the hardest weeknight group ride and burly enough for a little dirt-road adventuring on the weekend. They need to brake well in any weather. They need to be light, aerodynamic, durable, and good looking. With these goals in mind, testers were tasked with answering a simple question: which would they buy?

WIND TUNNEL TESTINGOn-road testing can only reveal so much. To delve into the realm of aerodynamic marginal gains, a wind tunnel is a must. So, Velo visited the A2 wind tunnel in North Carolina.

All eight wheelsets were tested with the same 23mm Michelin Pro4 tires, inflated to the same pressure (110psi). They were then mounted to a

BMC TMR01 aero road bike. Testing wheels off a bike — without the fork and frame that surround them during every ride — is a useless endeavor. The A2 tunnel always tests while the wheels are spinning, as they do in the real world, and that is how this test was performed as well.

At zero degrees yaw, a direct headwind, all of the wheels were tightly bunched. All clearly serve as effective fairings for the tire at this head-on wind angle, with only 14 grams of drag sepa-rating the fastest, the Ursus Miura, and the slow-est, Vision’s Metron 40.

At this particular wind angle, the width of the rim bed is vital. A narrower rim bed results in a narrower tire, which tends to be faster in a direct headwind. Hence, the narrow Ursus performed well, and the fat Vision less so.

However, a zero-degree wind angle is quite rare in the real world. More important is how a wheel performs as the wind moves off to the side, particularly in the 5- to 15-degree range. The most common wind angle that the average amateur cyclist will experience is somewhere between 6 and 8 degrees, according to a num-ber of manufacturers. Wheel companies design around this fact, and it is in this range that we begin to separate the best wheels from the rest.

Zipp’s 303 Firecrest was the clear winner. While drag for the other wheelsets slowly climbed as yaw angles increased, the Zipps’ drag began to decrease at 10 degrees. It dropped to a low point at 15 degrees, ending up a full 38 grams of drag (which equates to 4 watts at 25 miles per hour)

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66 VELO SEPTEMBER 2014 VELONEWS.COM

TECH & TRAINING » CARBON CLINCHER TEST

faster than the second best set, the Xentis Squad. Under the conditions in the tunnel, and on the

particular frame we used to test, the Zipps were faster at 15-degrees yaw than they were into a direct headwind — they were acting as sails.

Mavic’s CC40 wheelset achieved similar results across yaw angles, dropping at 15 degrees. But that wheelset’s drag fi gures were higher at 5 degrees and 10 degrees, so even with a dip at 15 degrees, it was still behind both Xentis and Zipp.

The Xentis wheels were a surprise. The odd wave pattern found just below the brake track seems like a gimmick, but perhaps there’s something to it. It was a clear second place at high wind angles, and performed well at 0 de-grees as well. It was average across the impor-tant 5- to 10-degree range.

The rest of the wheels were bunched closely to-gether. Reynolds had a spike at high wind angles, perhaps a result of its sharp rim profi le. The wheels from Mavic, Ursus, Bontrager, Enve, and Vision all fell within 24 grams of drag of each other. That’s a difference of 3 watts at 25 miles per hour.

MAVIC COSMIC CARBONE 40$2,750 WEIGHT: 1,558 GRIM DEPTH: 40MM71

ST BR

VA ACCW

68%

70%

80%73%

66%

Mavic was able to keep the weight of its CC40 rims quite low considering they are actually hybrids, a shell of carbon fi ber wrapped around an aluminum skeleton. That aluminum isn’t a cost-saving measure, though; it’s a heat sink. The Mavics are the best option for big riders, or anyone concerned with safety under hard braking.

WE LIKE • Aluminum shell inside the rim improves heat dissipation under braking

WE DON’T LIKE• Narrow rim isn’t a good match for wider tires• Brake track eats brake pads when wet

THE BREAKDOWNThe percentage of points available awarded to each wheel in scientific testing (ST), value (VA), crosswinds (CW), acceleration (AC), and braking (BR).

0

600

650

700

750

5 10YAW (DEGREES)

WIND TUNNEL RESULTS

DRAG

(GRA

MS)

AT 2

5 M

PH

15 20

VISIONMAVIC CC40URSUS

REYNOLDS 46

BONTRAGER D3ENVE 3.4

XENTIS SQUAD 4.2ZIPP 303

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74 VELO SEPTEMBER 2014 VELONEWS.COM

TECH & TRAINING » CARBON CLINCHER TEST

ZIPP 303 FIRECREST$2,700WEIGHT: 1,532 G RIM DEPTH: 45MM88

ST BR

VA ACCW

91%

85%86%

80%

93%

The venerable 303s offer the best aerodynamics, the best brake track, and the most predictable crosswind handling available today, all in one package. The hubs are a letdown, and they have been for a decade; we wish Zipp would simply offer its wheels with hubs from established brands like DT Swiss and Chris King, just as Enve does.

WE LIKE • Incredible stability in crosswinds• Predictable, powerful braking• Wide tire bed improves traction and comfort

WE DON’T LIKE

• A tad heavy• Hubs are not durable • Freewheel mechanism requires frequent maintenance

Spending our own cash, we’d buy the Zipp 303s every time.

The wind tunnel told the story best: The 303s were far and away the fastest of the bunch across the wind angles that matter most. The Xentis wheels came close, and a few others were faster into a direct headwind, but none could match the consistency of the 303s.

Braking was phenomenal, particularly in dry weather. The rim bed is wide, splaying out our favored 25mm tires into a wonderfully round shape, providing excellent traction and comfort. The fat Firecrest shape works some sort of magic in crosswinds, remaining utter-ly controllable even in nasty, gusty conditions.

There is one caveat, though. The backbone of the 303 is its rim design; that is clearly where Zipp’s engineers spend most of their time. The wheelset, as a whole, fell short in other areas. The company’s hubs have had issues in the past, and they still do. We had freehub problems within 1,500 miles. A bit of at-home cleaning and re-lubing was all that was required, but that’s still a poor showing given the price and apparent quality of the rest of the package.

In an ideal world, we’d build up the 303 rims with a better pair of hubs — something like the DT Swiss 240s that come on the Enve wheels.

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