Many top-level aero wheel makers including Zipp, Hed, Enve, and Bontrager are currently producing incredibly aerodynamic wheels with rims ranging from 50-70mm in depth. They’re all fast, but they’re similar. Wind tunnel testing can perceive small differences between most of them, but the gaps are minimal. The aero difference between tires is often larger than the gaps between these wheels.
As aero performance has converged to a similar standard, ride quality and usability have become increasingly important in distinguishing wheel performance. Easton is completely overhauling its wheels for 2014 and will be releasing a broad, mid-depth wheel called the Easton EC90 Aero 55. The new rim shape uses a broad cross section that is designed for speed, usability, and ride quality. As part of the effort to separate this wheel from the increasingly competitive class of 50- to 70mm-deep aero wheels, the EC90 Aero 55 is the first widely available tubeless-specific aero clincher.
Cars, motorcycles, and mountain bikes use tubeless clincher-style tires almost exclusively. Road bikes are one of the few wheeled vehicles that still rely on tubes to hold air. And tubes go flat.
A clincher rim with a solid spoke bed (and a few design tweaks to help the tire bead seat against the rim) is capable of running tubeless with minimal changes. A special valve, a tubeless-specific tire, and a little sealant are all that is required. Nipples thread into the inner diameter of the rim. And if anything goes wrong with the tubeless setup, these wheels can be used as standard clinchers as well.
The EC90 Aero 55 clincher was designed to run tubeless without the additional headache and pieces involved in converting a standard clincher. More shallow aluminum (read: not aero) road rims wheels are adopting this construction, and the EC90 Aero 55 is the first aero wheel to do so. Tubeless specific tires are thicker than standard tires, so rolling resistance is a factor when deciding to use a tube or tubeless setup for a race, although practically eliminating flats is a very appealing advantage.
While tubeless road wheels haven’t yet exploded as they did for mountain bikes, nearly 30 tubeless tires are currently available and the number is growing.
This rim is extremely broad, following the trend toward wide aerodynamic wheels that has taken place over the past five years.
Easton did its homework when designing this rim. The company tested 30 different prototypes before arriving at a final shape; it bought, and then tested, some of the leading aero wheels for comparison. Easton went to great lengths to get repeatable, reliable results including using the same 23c tire set for every test, running each trial at least three times and averaging the data, using a linear regression calculation to eliminate small variations, and testing in the same tunnel using the same fixtures.
Wind tunnel data doesn’t provide answers itself, and it has to be analyzed in a way that represents actual riding conditions. There is no universally agreed upon standard set of equations and conditions to represent cycling because of varied rider speeds, wind conditions, interaction with objects such as other riders, or things on the side of the road. Manufacturers try to get as close as possible to a realistic model, but none are perfect.
Easton adopted a formula called Wind Average Drag, developed decades ago to calculate semi truck aerodynamic characteristics. This equation drives the development of an aero product such as a wheel because wind drag changes as wind angle changes, and all the conditions that vary between riders and individual rides determine the wind yaw range that is most important for a particular cyclist. Easton calculated the average amount of time spent at every potential yaw angle when riding in a 6.6mph wind, the average wind speed over ground in the U.S., for a rider traveling 30 mph. The method is sound, although many riders average far below that lofty speed — the EC90 Aero 55’s sweet spot was tuned for riders much faster than the typical amateur.
The outcome is a rim that is 29mm at its widest point with a tapered brake track measuring 28.5mm at the center of an extremely blunted inner diameter. The tubular and clincher versions are shaped slightly differently, and Easton’s testing found the clinchers to be just barely faster in the wind tunnel.
Stability and ride quality
In addition to improved aerodynamics, broad clincher rims reduce rolling resistance and improve vibration dampening and cornering ability by increasing tire volume and pushing the sidewalls into a shape that can better resist cornering force without deflecting. The inner walls of the clincher EC90 Aero 55’s brake track are 19mm across, making it a very high-volume rim.
Like tire style, braking performance, and durability, stability in crosswinds is a big factor in aero wheel usability. Easton measured the steering input of different wind conditions, but did not go through a series of prototypes with the goal of reducing steering input from wind. Easton wheel engineer Scott Junker says the American company was happy with the results it got when comparing to ENVE 6.7 and Zipp 404 wheels, two sets we have subjectively found to be among the most stabile in gusty conditions, but opted not to share data because the results were not sufficiently rigorous to meet Easton’s standard for publishing.
To take the steering force measurement, Easton mounted a fake “arm” to a handlebar and measured the force applied to the arm in the full spectrum of wind conditions a cyclist is likely to experience. Like those other two rims, the Eason product has an extremely blunted inner diameter, which some wheel engineers have credited with improving stability compared to rims with a pointy tip.
First ride experience
From a single ride on the wheels, brake performance was impressive for a carbon rim. Stopping power was more than adequate with SwissStop Yellow King pads, as was modulation.
Gone are Easton’s previous hubs. They are replaced by the top-tier Echo hub and second-level V5. Some of the differences include a wider bearing stance to mitigate bearing wear by reducing the torque on the bearings that resist the torque created by pedaling. Two seals were added to the hub to prevent dirt from seeping into the bearings. Making the hubs more robust instead of lighter is another way Eason strove for durability and function over other goals.
The wheels will be available later this year, in early winter or late fall. The clincher version of the EC90 Aero 55 will go for $2,800 and the tubular set will be priced at $2,400. Campagnolo freehub bodies will be available. The tubular version weighs 1,330 grams (claimed) and the clincher comes in at 1,580 grams. Both use the Echo hubset. A disc brake version of this wheel will be available in the 2015 model year.