Enve wheels: can "aero" get any quicker?

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The new Enve wheels were developed in the Mercedes F1 wind tunnel in Brackley.(Image credit: Rob Monk & Will Ireland)

The Enve 6.7, the first wheelset in Enve's new aero wheel range developed in conjunction with Simon Smart, is set to go on sale in June. Over the past year, Procycling has tracked the development progress of these wheels from start to finish. Here's the inside line on what's gone into them to make them so fast.

The aero wheel market is packed and fiercely contested between several well established brands with many years of development behind them - you don't simply walk in. Lucas says the solution arrived by chance: "I'd come to the UK on business in March 2009 and I was watching the Australian Formula One GP in the hotel. Back then we were sponsoring Fly V which also had Virgin branding. Then on the television I saw the Brawn GP car wheeled out and it had a Virgin sticker on the nose. I made some calls and got a contact at Brawn GP and requested a meeting with them. They put me onto Simon Smart who had a contract to use their wind tunnel. From the first time we met I knew he was the guy we needed."

As well as having ten years of experience in F1 and two of the fastest and most successful time trial bikes on his CV, Smart is a keen and rapid time triallist himself. But most crucially, he was already thinking along the same lines as Enve. The development of the Giant and Scott time trial bikes had involved a lot of wheel testing and he'd soon started having ideas on how to make faster wheels than were currently offered. He just needed a manufacturing partner...

It was decided that the new range should consist of three wheelsets shaped to fit particular scenarios: a climbing and multi-purpose set, a mid-depth road race and TT pair, and a flat-out TT set. Smart first set about conceiving a new R&D method. With an agreed target of nothing less than ‘making the most aerodynamic wheel range in the world', and a number of ideas stored up from his work in frame design, Smart knew that faster wheels had to start from better testing protocols.

It was clear from the start that wheel testing had to be done in a bike. "it doesn't take Einstein to work out that when you put a wheel in the bike the flow it's seeing is being interfered with," said Smart. The current leaders in the aero wheel industry agree - Zipp and Hed developed their latest generations with Cervélo and Trek respectively. However, Smart wanted to extend the testing method further and give buyers a range of wheels that would work in a broader spectrum of bikes.

"The development of one wheel in one bike is limited because of the huge choice of designs out there. For example, you could [run your own test] with a Cervélo P3 and you'd choose a Zipp 808. You do the same test on another bike like the Trek or Giant and you'd choose a Hed S9. The consumers are completely baffled by all this information so really the strategy is to try to develop a range of wheels that work in many different bikes.

Smart's process therefore requires wheel concepts to prove themselves in two very different TT bikes, the Cervélo P3 and Trek Speed concept, and two road bikes, the Cannondale SuperSix and Specialized Tarmac. On top of this, the Scott Addict-based development rig built by Smart exclusively for Enve can include a dummy rider and ensures a high degree of accuracy for repeatable measurement of marginal improvements. Other metrics are recorded, too, but they're kept secret.

In terms of ride quality, the new aspect that Smart and Enve wanted to pursue was stability in crosswinds. Many wheels are sold on their aero performance at a particular crosswind yaw angle, "so you've got this sweet spot but can you ride it?" says Smart. "Many wheels are too unstable at their most effective angle. The big compromise is rim depth versus stability. So in the wind tunnel we're doing some really unique stuff. We're going to be the first to test stability in a wind tunnel. We've got a stiffness target, a weight target, a stability target and a drag target and we're going to put all those in the pot and test all these variations of rim width and depth."

The aims are to confirm the computer modelling and create a shortlist of rim cross-sections. There are at least 19 profiles to be tested - five overall shapes are narrowed down to two, then seven micro-variations of each – and all at a full range of yaw angles and in at least two of the four bikes Smart has picked out. A measurable change in aerodynamic behaviour and crosswind stability can be seen from a change to the rim width as small as 0.2mm.

There's a huge amount of work to get through but behind the focus is nervous excitement. even if they won't quite say as much, it's a very big day in Enve's ambitious future. in attendance are: Brett Satterthwaite, Enve co-founder, fluid dynamicist and civil engineer; Kevin Nelson, design engineer; marketing VP Lucas, who also has a construction engineering degree; and mechanical engineer and ex-F1 aerodynamicist Smart. in this company, Procycling feels extremely unintelligent and concentrates hard on not asking stupid questions.

With so many performance targets, aesthetics couldn't be a factor even if Enve - never knowingly overstated - wanted it to be. "We're straight down the line form-follows-function. if the fastest shape looks like a cow then the new wheel will look like a cow," says Lucas. While it's already near certain that the new wheels will actually be black and round, they will differ significantly from anything else on the market, as Smart explains:

It's one thing for a wheel to be aerodynamically effective in a varying crosswind but it's quite another for it to be rideable. Ease of handling and confidence stem from predictable behaviour which in turn owes everything to a linear response from the wheel as the crosswind changes. As is so often the case in any interaction between man and machine, from the brakes in your car to your PC's mouse, linearity allows the user to calibrate their actions and working in harmony with the machine – in this case, their bike.

Smart's wind tunnel rig allowed him to measure the steering torque applied to the front wheel by a crosswind. Baseline tests with existing wheels that were known to be tricky to ride in gusty conditions showed a non-linear response to crosswinds. That is, as the wind angle increases you might have to steer into it more but then if it increases again past a certain point then you would need to steer against it a lot less.