Friday, November 9, 2012

Velonews, Speed for Purchase

Velo July 2012. Photos by Brad Kaminski

Editor’s Note: In April 2011, we unveiled VeloLab, our in-depth bike and component testing program that combines objective, lab-based metrics with on-the-road evaluation. In the 18 months since, we’ve tested more than 25 bikes, from sub-$1500 budget road racers to the bikes of the WorldTour. We’ve even given four commuter rigs a spin and tested a run of seatposts for vibration. In our November issue, Lennard Zinn puts five different tubular tires through the paces in Finland to determine the effects of tire size and air pressure on rolling resistance. The following VeloLab test first appeared in our July 2012 issue and pits five aerodynamic carbon wheels against each other: the Psimet/White Industries Custom, the Rolf Prima 60, the Hed Stinger 6 Flamme Rouge, the Bontrager Aeolus 5 D3, and the Enve System 6.7.

Speed for Purchase: Five Aero Wheels Under the Microscope

At its core, cycling is an equation: forces for, and forces against. Subtract that which seeks to slow you down — rolling resistance, wind, gravity, grinding bearings and all the rest — from the amount of power the human engine is churning out. The result? Speed.
There are two ways to go faster: improve the engine, or reduce resistance. The former involves sweat and tears. All other things being equal, reducing resistance anywhere on your bike or body will result in a faster ride. Yes, you can buy speed. It takes a decent pile of cash, and a willingness to accept a few minor drawbacks, but it is possible. And that’s where these aero wheels come in.

A New Breed

Compared to a standard 32-spoke aluminum wheel, the 50-70mm deep wheelsets in this test will reduce drag by between 158 and 224 grams at 30 miles per hour. What does that mean for you? That roughly equates to 15 to 23 watts. It might not sound like much, but it takes a hell of a lot of sweat to become 23 watts stronger.
The use of computational fluid dynamics (CFD) to help refine rim shape — which has the most dramatic effect on aerodynamics and control — has allowed for an exponential increase in aerodynamic refinement over a very short period of time.
The result has been a surge of new rim shapes, all of which attempt to increase a wheel’s stall angle, or the wind angle at which most of the aerodynamic benefit is lost. All use a similar theme: wider than ever at the brake track, between 24 and 28mm, and wide all the way to a rounded spoke bed. Though no two are identical, all have more in common with each other than with the narrow V-shaped profile used for most of the last decade. All claim to be faster, and offer vastly improved crosswind stability.
For this test, we included a classic V-shaped carbon rim, plus blunt-tailed options from Rolf, Hed, Enve and Bontrager. All five are tubulars, though most come in a clincher version. Zipp opted out of the test.
We put each set through extensive wind tunnel and inertia testing, plus real-world ride time, and ranked them in a number of objective and subjective categories, including brake performance and crosswind stability. In the wind tunnel, we tested various tire sizes on each wheel, since the tire/rim interaction is vital to overall aerodynamics.
In the end, each company took a slightly different approach toward the same goal: a fast, light and stable set of race wheels. Read on to find out which was most successful.

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