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Tech Talk: Bontrager and the importance of being aero’

The folks at Bontrager took an opportunity at last week’s Tour de Georgia to introduce additions to the brand’s high-end road racing product lineup. Major additions include an expansion of the Aeolus deep-dish aerodynamic wheel line as well as a new time trial disc wheel – all produced under a partnership with HED Cycling Products. Why aero?For the last few years riders have put a premium on weight and all but ignoring aerodynamics. Recently, even at the sports top level, aerodynamic advantage has only been considered when it comes to time trialing. But whether you look at a grand tour

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By Matt Pacocha

The Aeolus 6.5...

The Aeolus 6.5…

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The folks at Bontrager took an opportunity at last week’s Tour de Georgia to introduce additions to the brand’s high-end road racing product lineup. Major additions include an expansion of the Aeolus deep-dish aerodynamic wheel line as well as a new time trial disc wheel – all produced under a partnership with HED Cycling Products.

Why aero?
For the last few years riders have put a premium on weight and all but ignoring aerodynamics. Recently, even at the sports top level, aerodynamic advantage has only been considered when it comes to time trialing. But whether you look at a grand tour stage racer or your casual weekend warrior, it quickly becomes apparent that the majority of riding is done in undulating terrain, not mountains, where aerodynamics trump weight.

Bontrager designers realized this and saw the impacts it can have in a stage race, whether it is in a small breakaway or chasing one down. To step up its aerodynamic game, Bontrager entered into a partnership with long time aero’ consultant, Steve Hed, who has worked with the Postal/Discovery team for the last eight years.

“Steve Hed is probably one of the most brilliant aerodynamic guys in cycling,” said John Balmer, Bontrager’s director of product management. “Steve is able to look at something – I’m pretty sure he can actually see air movement – and predict things that take a number of rounds of software and wind tunnel tests to validate.”

... and a closer look.

… and a closer look.

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The relationship between Bontrager and HED became apparent in the last two tours where HED wheels found steady use on the Discovery time trial bikes. This eventually led to a partnership with HED allowing Bontrager to offer its co-designed products to consumers. The first result of that partnership, the tubular Aeolus 6.5, was introduced at last year’s Dauphine just before the 2005 Tour de France. George Hincapie and Yaroslav Popovych rode the new wheels to first and second place in the last stage on a very hilly rolling circuit. From there the wheels saw action in the Tour.

“A lot of times it was put on the mainline riders, the domestique’s bikes, because those poor guys are on the front of the peloton driving the pace for the first three quarters of the race,” said Balmer. “They are really out there in the wind, so they need something that they could depend on, something that was going to give them a very fast bike.”

One Bontrager wheel designer on the project, Brad Addink, explained that even the Discovery Team needed to be educated of the value an aerodynamic product could have over something that was designed to be purely lightweight.

“I have convinced the Discovery Team to ride the 5.0s in almost any condition,” said Addink. “They were riding the XXX Lite tubular box section rim on hilly stages, and I go, ‘what percentage of the time are you actually climbing during that hilly stage – maybe 20 percent?’ Say you had 100k to get to that climb, during that 100k if you have to chase down a break or whatever else you need to be on the [Aeolus] 5.0s. It usually takes about a 100 plus grams in wheel weight, before a super light wheel will be faster than an aerodynamic wheel.”

Design and Construction
The first Aeolus only came in a tubular version and only in a 65mm height. Bontrager will add four new models, which will be available by mid-summer. The Aeolus 5.0 and 6.5 will be offered in tubular and clincher versions, while the Aeolus TT is a new tubular only TT disc wheel.

“There are a lot of times you look at a wheel and you simply say, ‘I want to make this wheel as light as possible,’ and that’s great,” said Balmer. “You can do that with minimal surface areas and small bearings, small hubs, but the fact is those won’t hold up for a season in Europe. They’ll be destroyed, you’ll ruin tires, you’ll blow bearings, they won’t hold up. That’s not what we wanted. We want a product that when we load it up under a pro team, that team can go out there with confidence and use it in virtually any condition.”

Bontrager and Hed’s designs are married in the Aeolus line. Bontrager provides the rims, its OCLV carbon tubular or clincher, which are produced in Waterloo. They are then sent to the HED facility where the aerodynamic skins are bonded to the rims.

“The skin that goes onto the wheel is not a fairing, it is a structural element,” said Balmer. “There is not much lateral support from the skin, it’s more radially, up and down. It gives it [the wheel] enough radial strength so we can reduce the spoke count down to 16 spokes, which is also the UCI minimum.”

The covered rims are then shipped back to Waterloo where Bontrager employees do the inspection of the co-produced rim, then the assembly, truing and shipment of the wheels. Racing in Europe has influenced Bontrager’s designs in a number of ways. One of the most resounding is the use of a 22mm wide rim.

“On a tubular it gives us more gluing area, it also gives a bigger bed to hold the tire,” Balmer said. “It gives the tire a better profile as it goes to the ground, particularly on a clincher, because your rim width definitely influences your tire shape. A wider rim will change that contact patch significantly.”

The Aeolus deep section wheels will come in two styles, the new 5.0, which features a 50mm rim height and the 6.5 featuring a 65mm rim. Both wheels will be offered with Bontrager’s 110 GSM (grams of carbon per square meter) OCLV rim in tubular or clincher styles. The suggested retail price is up there, $2500 for the tubulars and $3000 for the clinchers regardless of rim height. The 6.5 tubular is currently available. The 5.0 in tubular will be available at the beginning of May. The clinchers are set to take a bit longer, the 6.5 is slated for release at the beginning of June and the 5.0 at the beginning of July.

Tech Talk: Bontrager and the importance of being aero’

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Aeolus TT
The wide rim is also used in the Aeolus TT, Bontrager’s disc wheel. “This wheel provides the best of both worlds between a flat disc wheel and a lenticular disc wheel,” said Balmer. “To that end we developed a wheel with three different radii across it.” The first radius is the lenticular, which refers to its lens shape, meaning it has different shape at the hub flange than at the rim’s base. A flat disc is simply dead flat. The Aeolus TT transitions from a 36mm width at the hub down to its standard 22mm wide rim. The third radius, a bulge placed 22mm from the rims inner edge, disrupts airflow coming off of the disc and pushes it smoothly over the tire, while adding considerable stiffness. The three radii are designed to control airflow, but they also increase the wheel’s lateral stiffness.

“A typical disc wheel has issues when you’re really powering on the thing,” said Balmer. “You get a whole lot of distortion across it because of a lack of support. These additional radii were put in there, again to control airflow, but more to stabilize it laterally to make a more efficient wheel.”

The wheel is constructed in HED’s factory, as a tensioned disc, meaning the outer skin supports the connection between the hub and OCLV rim. Unlike the other Aeolus models, the TT utilizes Bontrager’s 55 GSM rim instead of the 110 GSM rim. This is purely in an effort to keep the wheel’s weight down. Bontrager paid attention to every detail of this wheel including the non-drive axle, which was given an aerodynamic shaped endcap. This cap is said to cut five grams of wind drag, while only adding about 20 grams to the wheel’s weight. The Aeolus TT’s price has not been set, but it will be available at the beginning of August.

If the Aeolus TT follows the evolution of the spoked Aeolus wheels, it is easy to speculate that Bontrager may have a full carbon clincher TT disc waiting in the wings. But for now, Bontrager will have a chance to revel in these additions to their ProTour level wheel line.

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