Bontrager claims best-in-class drag, stability and weight for new Aeolus XXX wheels

10,000 rims shapes analyzed in two-year project

Bontrager’s new Aeolus XXX wheels are faster and more stable than comparable models from Zipp and ENVE, the Wisconsin company claims.

Trek and Bontrager engineers spent more than two years on the project, incorporating FEA, CFD, optimization software, wind-tunnel work and feedback from pro riders. Some 10,000 potential rim shapes were analyzed, the company claims.

By melding engineering work with real-world analysis — like having test riders flag points in rides where they felt unstable and crosschecking that against wind and side-force data — Bontrager claims it now has the best all-around wheels you can buy.

The Aeolus XXX come in 2, 4, and 6 models, for 20mm, 40mm and 60mm rim depths
The Aeolus XXX come in 2, 4, and 6 models, for 20mm, 40mm and 60mm rim depths

Building on the Aeolus D3 wheels launched in 2011, Bontrager spent two years developing the latest Aeolus XXX line of aero wheels that come in 28mm, 47mm and 60mm rim profiles. The wheels have a whopping 21mm internal-rim width and 27mm or 28mm external brake-track widths but a more pointed shape than the snub-nosed spoke bed we have come to expect from wheels with a ‘stable in the crosswind’ claim.

The wheels also have a new textured brake track.

Quantifying ‘stable’ on the road

“One thing we often heard was, the deeper the wheel, the less confident riders felt,” said Bontrager chief engineer Eric Gertner. “It seemed like there was no way around it. But [engineers] Claude Drehfal and Mio Suzuki came up with a way to optimize for speed and stability.”

The project began with a research study to understand stability. While weight, deflection and even aerodynamic drag (given set parameters) are fairly straightforward to measure, what ‘feels stable’ is not.

CFD was one of the tools used to design the rim shape. Here, airflow at three wind angles is calculated
CFD was one of the tools used to design the rim shape. Here, airflow at three wind angles is calculated

“We noticed two things with deep wheels in the wind: You feel like you’re being blown over, and you feel the wind is grabbing the front-wheel steering,” Gertner said.

To put numbers on things, Bontrager engineers went to a wind tunnel and took measurements of side force and different torques put onto different rim shapes at certain yaw angles.

Next, they sent test riders out on an instrumented bike that measured wind speed and yaw during their rides. Whenever they felt unstable, the test riders would hit a button to record the moment, then after the ride engineers would correlate those with tunnel data for side torque.

Bontrager engineers determined that moments of instability don’t just occur when a wheel stalls (when airflow breaks free from the wheel), but also when there is a gust or a change of direction in the wind.

HEEDS is an optimization tool Bontrager used for its iterative design
HEEDS is an optimization tool Bontrager used for its iterative design

The engineers defined instability as anything that caused a steering torque of .75N-m or greater in less than 1.4 seconds. Then they designed around that, while still trying to make the wheel as fast as possible in a variety of wind angles.

“We tried to minimize side force, as that has the largest impact of steering force overall, while minimizing drag at the same time,” Drehfal told BikeRadar.

Bontrager used a HEEDS parameterized optimization software that integrated with their CAE tools. Some 10,000 potential shapes were analyzed, Bontrager claims.

Bontrager used HEEDS to fine tune the balance of aero drag and side-force stability
Bontrager used HEEDS to fine tune the balance of aero drag and side-force stability

Wind tunnel confirmation

After Bontrager had the wheel designs fairly dialed in, the engineers went back to the wind tunnel.

“The first step is a really good CAD model,” he said. “We need to start with something good in the wind tunnel. We looked at how outer and inner rim width will affect drag. Then we optimized shape parameters of the rim.”

All the wheels were optimized around a 25mm tire, which acts as a nose cone when nestled inside the 21mm wide rim, which is 27mm wide at the brake track for the 2 and 4 and 28mm wide for the 6.

Previous Aeolus D3 wheels had a 19.5mm internal rim width and a 27mm max outer width.

Internal rim width is massive
Internal rim width is massive

“We cut prototypes in alloy or plastic of our three best shapes, within less than .2mm,” he said. “And then we used the tunnel to confirm what we measured in CFD.”

The end result, the company claims, is a wheel with the lowest side-force-to-drag ratio of anything on the market.

So, for example, the XXX 6 has a claimed side force of 750+g at less than 100g of average drag across 0-20 degrees, compared to ENVE 6.7’s 800+g at more than 100g drag or Zipp 404’s 750+g and more than 110g of drag. All these figures are according to Bontrager measurements.

Lower-profile wheels in general have higher drag and lower side force, but here Trek also claims its Aeolus XXX design trumps the competition.

The 4 and the 6 rims have more of a pointed spoke bed than some other relatively stable aero wheels
The 4 and the 6 rims have more of a pointed spoke bed than some other relatively stable aero wheels

Weight, stiffness and braking

Although reduced drag is the primary point of aero wheels, Bontrager and other companies certainly pay attention to the other characteristics that affect the ride: weight, stiffness, strength and braking.

Claimed rim weights for the Aeolus XXX are 370g for the 2, 430g for the 4 and 500g for the 6. Compare those to Zipp’s 412g 202 NSW, 458g 303 NSW and 496g 404 NSW. Total wheelset weights are slightly lower for the Bontrager than the Zipp wheels, according to Bontrager.

SwissStop Black Prince pads handle the stopping
SwissStop Black Prince pads handle the stopping

Bontrager engineers said the layups were designed for a stiff wheel that didn’t feel harsh.

A new laser-etched brake track brings wet and dry braking performance in line with alloy rim-brake models, Bontrager claims, without any squealing or loud noise. The textured surface is designed to work with SwissStop Black Prince pads.

The brake track texture is subtle. Compare it to the height of the XXX sticker
The brake track texture is subtle. Compare it to the height of the XXX sticker

DT Swiss internals – and hub options

All the wheels come with DT Swiss hub internals, including the 36-point star ratchet engagement in the rear hub.

The wheels come in clincher and tubular rim-brake models, plus disc-brake models in all three rim depths.

This pair of Aeolus XXX 6 clinchers weigh 1,600g
This pair of Aeolus XXX 6 clinchers weigh 1,600g

Aelous XXX pricing, weights and availability

Unlike some companies that launch a product well ahead of its availability, Trek has established a pattern of launching the day something goes on sale, and the Bontrager Aeolus XXX wheels are no different. The Aeolus XXX wheels are available now, in clincher and tubular rim-brake models, as well as disc-brake models, for the 2, 4, and 6 rim depths.

Pricing for all wheelsets is £1,999 / $2,399 / €2,399.

Wheelset claimed weights are as follows.

Aeolus XXX 2 TLR – 1,305g                             2 Tubular - 1,150g

Aeolus XXX 2 TLR  Disc – 1,380g                    2 Tubular Disc - 1,230g

Aeolus XXX 4 TLR  - 1,400g                             4 Tubular - 1,270g

Aeolus XXX 4 TLR Disc – 1,455g                     4 Tubular Disc - 1,330g

Aeolus XXX 6 TLR – 1,530g                              6 Tubular - 1,380g

Aeolus XXX 6 TLR Disc – 1,600g                     6 Tubular Disc - 1,455g

Ben Delaney

US Editor-in-Chief
Ben has been writing about bikes since 2000, covering everything from the Tour de France to Asian manufacturing to kids' bikes. The former editor-in-chief of VeloNews, he began racing in college while getting a journalism degree at the University of New Mexico. Based in the cycling-crazed city of Boulder, Colorado, with his wife and two kids, Ben enjoys riding most every day.
  • Discipline: Road (paved or otherwise), cyclocross and sometimes mountain. His tri-curious phase seems to have passed, thankfully
  • Preferred Terrain: Quiet mountain roads leading to places unknown
  • Current Bikes: Scott Foil Team Issue, Specialized S-Works Tarmac, Priority Eight city bike... and a constant rotation of test bikes
  • Dream Bike: A BMC Teammachine SLR01 with disc brakes and clearance for 30mm tires (doesn't yet exist)
  • Beer of Choice: Saison Dupont
  • Location: Boulder, CO, USA

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