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January 30, 2013
Bontrager recently redesigned its Aeolus wheels and expanded on the number of models in its range. The Aeolus 3 D3 is the lightest wheel on offer and is aimed at climbers looking for light wheels that also offer a significant reduction in aerodynamic drag. This wheelset may also be the best all-rounder on the market thanks to its superb handling in crosswinds.
Bontrager introduced its Aeolus wheelset around 7 years ago in collaboration with HED. Bontrager manufactured the rims and HED provided the “skin”, a sort of fairing that acted to strengthen the rim and reduce aerodynamic drag. Carbon rims were introduced soon after and the rims remained largely unchanged until Bontrager’s engineers overhauled the Aeolus range for 2012 (this time, without the assistance of HED). The aerodynamic skins were abandoned in favour of a one-piece shape that was developed and refined by extensive computer modelling (specifically computational fluid dynamics). Interested readers can learn more about the design process by reading Bontrager’s white paper but in short, computer modelling allowed engineers to assess thousands of virtual prototypes before constructing a few actual wheels for wind-tunnel testing.
The new Aeolus D3 (Dual Direction Design) wheels are exceptionally wide (27mm) and there are four models to choose from that differ only in rim depth: Aeolus 3 (35mm rim), Aeolus 5 (50mm rim), Aeolus 7 (70mm rim) and Aeolus 9 (90mm rimm). According to Bontrager’s testing, the aerodynamics of the Aeolus D3 range compares well with wheels from Zipp and HED (see Figure 1). However, the new wheels appear to be as good as anything on the market, the rims are roughly 10mm shallower (Figure 2), achieving perhaps the simplest solution for improving the handling of the wheels in crosswinds. All told, Bontrager have made their intentions clear in overhauling its Aeolus range, they want to take a share of the market away from Zipp and HED.
An overview of the aerodynamic drag of the Aeolus D3 range compared to some benchmarks. Data taken from http://media.bontrager.com/images/features/201108_aeolus/bontrager_aeolus_d3_wheels.pdf
The average drag for Aeolus, Zipp and HED wheelsets is inversely proportional to rim height, however Bontrager's wheels are distinguished by delivering similar drag with shallower rims.
BEFORE THE RIDE
The Aeolus 3 D3 is positioned as Bontrager’s climbing-specific wheelset. However, the all-carbon OCLV rims also provide significant reductions in aerodynamic drag, matching Zipp’s old 303s and outperforming their 202s (but not the new Firecrest 303s) (Figure 3). At 1150g, the 3 D3 tubulars compare well with 202 tubulars (1115g), while the clinchers are much heavier (1440g) and well outside the climbing-specific category. All told, the numbers promise a set of tubulars that are more versatile than a dedicated lightweight wheelset.
The aerodynamic drag of Aeolus 3 D3 tubulars compared to wheelsets from HED and Zipp.
The Bontrager-branded hubs at the centre of the Aeolus 3 D3 wheels are made by DT Swiss and feature carbon bodies and alloy flanges. The hub flanges are white, which makes an effective contrast for the carbon hub bodies and rims but also promises to drive any owner mad should they try to keep them clean. The freehub utilises DT’s double-ratchet system that allows for tool-free servicing and a choice of three interchangeable freehub bodies (Shimano 10 speed/SRAM, Campagnolo, and Shimano 11 speed). The hubs spin on oversized hollow alloy axles and cartridge bearings, while deep end plugs and rubber o-rings act to protect the bearings from the elements. DT also provides its straight-pull Aerolite bladed spokes for the build, 18 up front (laced radially), and 24 for the rear (2-cross for the drive-side, radial for the non-drive side) with external alloy nipples. Unfortunately, the test wheelset arrived sans Bontrager’s skewers so I can’t provide any detail on them but expect a pair if you buy these wheels.
As mentioned above, the rims are 27mm wide, wide enough to protrude beyond the sidewalls of 23-25mm tyres, which seems at odds with the aerodynamic design of the rims, however the extra width actually aids the aerodynamics of the wheels. The extra width also means lower tyre pressures–I settled on 80-85 psi for 23mm tyres–and better contact with the road. The test wheels were glued with Bontrager’s XXX Lite tubulars, which have a high thread count (290 tpi), Kevlar reinforcement and puncture protection.
Bontrager supplies two pairs of cork brake pads (to suit Shimano or Campagnolo pad holders) with each wheelset that must be used at all times. The pads are simple to fit however the calipers must be set well outside the sweet spot for their mechanical advantage and reassuring brake feel to accommodate the extra wide rims. With all the time and resources devoted redesigning the rims, some low profile brake pads should have made it off the drawing board to compensate for the extra rim width. It’s possible thinner pads are more prone to overheating, even when they’re made of cork, in which case Bontrager should have designed a low-profile pad holder or brake shoe to suit the wide rims. My Campagnolo calipers were able to accommodate the rims without any trouble, but not all calipers will (eg early SRAM). Likewise, the stays of some frames may also be too narrow for these wheels, so potential buyers should fit a set to their bike before placing an order.
The recommended retail price for Aeolus 3 D3 tubulars is $2598, while the clinchers cost $2998. The wheelset comes complete with skewers and a wheel bag, plus two pairs of brake pads and 2 valve extensions. For more information, visit the Bontrager website.
AFTER THE RIDE
The first thing I notice when I put a set of light wheels on my bike is how easy they are to ride. Every pedal stroke seems to require a little less energy and it’s really easy to make the bike surge ahead on any slope. While both of these traits were apparent during my early rides on the Aeolus 3 D3 tubulars, it was their behaviour in the wind that really stood out. The front wheel was completely unperturbed by crosswinds–which is to be expected for a 35mm deep rim–but what wasn’t expected was how well they kept turning while riding into a headwind. I don’t have any data to support my impressions but I found it easier to ride into a headwind with these wheels compared to my regular alloy clinchers (24 spoke HED Belgium rims). I presume the low spoke count and the aerodynamics of the rims were in my favour; add to this their low weight and easy acceleration on any slope, and you have a wheelset that anyone can appreciate.
In general terms, the Aeolus 3 D3 provided a smooth and predictable ride that I could take for granted after an hour or two in the saddle. The wheels are stiff but not rigid, they responded well to out-of- the saddle accelerations, but they didn’t excel in this regard. The Bontrager tubulars tyres look sensational on paper, they have a high thread count and the claimed weight is low, however I found them quite dull to ride (ie far from supple). My guess is that the puncture resistance is responsible for much of the dullness–in the absence of long-term testing, I can’t comment on how robust these tyres are–but I’d prefer to ride on something that is more supple such as Vittoria Corsa CX tubulars, even if it is more susceptible to punctures.
I’ve already described how the setting up the D3 rims on the bike had a detrimental effect on brake feel (since there was very little tension on the caliper spring) however this did not translate to poor braking. Indeed, brake performance was good enough to control the speed of the bike under all but the most demanding of circumstances. Cork is a great material for carbon-specific brake pads because it is very resistant to heat, however it lacks the kind of grip that allows for sudden braking and rapid slowing. The Bontrager brake pads suit predictable situations–I just found myself allowing for a little more braking distance–but I’d be reluctant to recommend these wheels for demanding bunch rides or rain-soaked races.
As the new year started, so did my training in the hills and the Aeolus 3 D3 wheels helped to ease me into my efforts. However, they did not transform me into a star climber, nor did they help close the gap to my stronger riding buddies. A weight saving of ~500g thanks to these wheels translates to less than 1% of my total weight, but they were still very pleasant to ride uphill. It was on the return trip along flatter roads where they may have paid a dividend, as I was able to take a longer pull on the front and drop one of my buddies. I’ll leave it to somebody else to perform a definitive study of the aerodynamics of Aeolus 3 D3s, Zipp Firecrest 303s, and Enve SES 3.4s to settle the dispute over the best lightweight carbon all-rounder, but for me, the 3 D3s stand out for their lack of susceptibility to crosswinds.
Over the last year I’ve managed a small survey of the carbon wheel market, riding Corima Aero+ clinchers , Zipp 202 tubulars , Enve SES 3.4 tubulars, and Reynolds Assault clinchers.
Now I can add Bontrager Aeolus 3 D3 tubulars to this group and it makes for a diverse bunch. Comparisons within this group are almost futile–sure, they all have strengths and weaknesses, but they make for different personalities that are difficult to rank in absolute terms. Ultimately, my scores reflect how well the wheels meet my priorities, which are the quality of ride and their ability to inspire or enable me to ride at my best. In this regard, the Aeolus 3 D3 wheels are the current leaders on my scoreboard but I’m not planning on buying them any time soon. The wheels are great performers but the braking needs to be sorted out to make them truly desirable.