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Roll with it - Spotlight on Formula One wheels 17 Dec 2009

McLaren wheels and Bridgestone tyres. Formula One World Championship, Rd 3, Chinese Grand Prix, Preparations, Shanghai, China, Thursday 16 April 2009. Lewis Hamilton (GBR) McLaren Mercedes MP4-24 front wheel spinner detail. Formula One Testing, Day Four, Barcelona, Spain, 12 March 2009. McLaren wheel detail. Formula One World Championship, Rd 16, Brazilian Grand Prix, Preparations, Interlagos, Sao Paulo, Brazil, Thursday 15 October 2009. Tyre marks in the pit lane. Formula One World Championship, Rd 18, Brazilian Grand Prix, Qualifying Day, Interlagos, Sao Paulo, Brazil, Saturday 1 November 2008. Heikki Kovalainen (FIN) Mclaren MP4-23 crashes into the tyre wall. Formula One World Championship, Rd 4, Spanish Grand Prix, Race, Barcelona, Spain, Sunday 27 April 2008.

Formula One racing is a difficult beast to master, with team, car and driver all striving in unison to deliver the best possible performance. There’s no doubt that collectively the package is greater than the sum of its parts, but if we’re dealing in cliches, then it’s important to remember that winning is in the detail, and in F1 racing there is nothing more important than details.

The ultimate representation of this is the car itself. From nose to tail, the design of a car embodies a team’s pursuit of perfection. Any element, however small, can make or break a race, even a season, and within every car, every part has been honed (and honed some more) to ensure it won’t let the team down.

Easy to overlook, and often overshadowed by those much-talked-about tyres that surround them, wheels are an interesting case in point. An insignificant, homogenous chunk of metal that all teams run they are not. In fact, the rivalry between the sport’s wheel manufacturers is just as fierce as that between engine suppliers and the work that goes into a team’s wheels easily rivals that for any other component.

The FIA’s regulations for wheels are surprisingly brief. Their number is fixed at four (remember Tyrrell’s six-wheeled P34 from 1976?) and they must be made of one homogenous metallic material. Their width, when fitted with Bridgestone tyres, must lie between 305 and 355mm at the front and between 365 and 380mm at the rear, while complete wheel diameter must not exceed 660mm when fitted with dry-weather tyres, or 670mm when fitted with wet-weather tyres. From there on in it is largely left to the teams - and their wheel partners - to design and manufacture the best on the grid.

Needless to say this relative flexibility in the rules, and the very real performance advantage to be gained, has led to some long-lasting partnerships between team and supplier. Eight-time constructors’ world champions McLaren have worked with Enkei for over ten years. One of the largest OEM (original equipment manufacturer) wheel suppliers in the world, the Japanese company produce more than 10 million wheels a year across every continent. For McLaren, deciding on - and sticking with - Enkei was a clear-cut decision.

“There is no doubt that Enkei is an extremely knowledgeable and competent company on all aspects of wheel design and manufacturing,” says senior McLaren design team member, Luca Furbatto. “Enkei's desire to perfect their products over the years, enhancing performance and quality at every opportunity, is aligned with McLaren's vision and values.”

That partnership starts on paper at Enkei’s base in Japan. After McLaren have specified design targets, including maximum weight, hub design, stiffness and installation requirements, a team at Enkei get to work, creating a number of ideas before showing McLaren its final proposals, typically numbering around 20.

In wheel design, the balance between strength and weight is absolutely critical. Too heavy and the car will lose performance, too weak and there is a risk of failure. It’s a real tightrope walk, and to gauge it correctly Enkei are reliant on simulated circuit data supplied by McLaren. With that data and using a process called ‘finite element analysis’, Enkei - after a lot of number crunching - are capable of predicting the durability of a component on each track on the calendar.

Interestingly, although the wheel is the only part of an F1 car in contact with the tyre, there is no direct design involvement from Formula One racing’s official tyre supplier, Bridgestone. However, with Bridgestone following the ETRTO (European Tyre and Rim Technical Organisation) specifications, which define several of the wheel’s key features like lip profiles and the recesses for tyre mounting and dismounting, there is no real need of any outside input, apart from, of course, McLaren’s.

And every year the McLaren-Enkei partnership strives to think up new ways to improve the technology and give the British team a competitive advantage over their rivals. Evolving the design is a constant aim for both parties, and like everything in F1 racing, is a very in-depth process. To put it into context, five months ahead of the 2010's first race, Enkei and McLaren had already formalised the season's wheel design and specification ready for production at Enkei’s factory.

“The wheel design changes every season as we always want to perfect and optimise the final product,” explains Furbatto. “We review the production cycle regularly and we're keen to implement new features all the time, from enhancing tyre-fitting to a lighter paint finish, from more elaborate machining detail to the aerodynamic interaction between rims and car aerodynamics.

“Moreover, there are aspects related to the fitting speed of tyres during pit stops that are very important to the overall outcome of the race. There are also aspects related to managing the differences in shapes and weights of different tyre specifications (for example, wet tyres have a different weight compared with dry) during an event that require a degree of attention in order to keep the car legal at all times.”

The partnership must also respond to any regulation changes that come into force from season to season. For 2010, when wheel designs must be homologated prior to the start of the season, those regulations are set to be tightened by the FIA. But like any good F1 engineer, when opportunities are reduced in one area, Enkei look to maximise those elsewhere within their design.

“As a wheel manufacturer, we enjoy the freedom of being able to improve and update our products for each new season,” explains Takeyoshi Terada, executive officer of Enkei’s marketing department. “For 2010, however, new FIA regulations - such as prescribing minimum rim thickness in several areas - means there is less freedom available now. That simply means we’ve assigned our efforts to different areas. The wheel spokes and hubs are less regulated, and we are free to develop more intensively in those areas.”

Next year’s cars will also have narrower front tyres, and will weigh more at the start of a Grand Prix due to a ban on refuelling. This, combined with new spending constraints, has made for interesting times in McLaren's and Enkei's design departments.

“In terms of differences for next season we expect large changes in 2010 because of constraints on costs, smaller front tyre sizes (12 inches instead of 12.75) and heavier cars,” says Furbatto. “Due to the financial restrictions imposed by the recession and by FIA/FOTA, the challenge on wheel design will move towards less expensive wheels or more durable wheels with, for example, a life-span of more than 5,000km."

With so much change from one season to another, it’s no surprise that over the last decade wheel design and manufacture has come on in leaps and bounds, with a constantly evolving approach making for real gains on track. Ten years ago wheels weighed four kilos, whereas this season they were 3.6. Contemporary designs are also considered over 20 percent more efficient than those of the late 1990s.

There have been major steps forward in manufacturing techniques. Whereas before the magnesium used to make the wheel would be cast, now it is forged in the Enkei factory under a massive 9,000-ton press. Turned to create the basic shape and profile, the wheel is then milled using a five-axis machine to create the spokes. Ten years ago two-axis machinery was typically used, but this modern five-axis jig allows Enkei to achieve Formula One levels of quality and consistency. It’s an intense process, but in reality the company’s work has only just begun.

“We also machine the hub and additional holes for the tyre valve and pressure sensors,” explains Terada. “Once the basic wheel is completed, it is thoroughly inspected and undergoes a series of non-destructive checks before being degreased, painted, lacquered and re-inspected for appearance and paint finish. Finally, each wheel is boxed individually and sent to McLaren.”

It’s a big shipment. Over the course of this year’s 17-race calendar McLaren used around 350 wheels. “On a race weekend each driver can use up to 21 sets of tyres between dry tyres, wet tyres and extreme wet tyres (or 84 wheels) so we are typically bringing 180 wheels to each event altogether,” says Furbatto. “We tend to use new wheels for races but inevitably, as the season progresses, we also begin to use low-mileage wheels for some races. We also need wheels for aero tests, demo runs and off-season testing, so the logistical problems of shipping wheels around the world whilst maintaining a sensible stock are not easy to solve."

Although Enkei do not send representatives to each race - McLaren look after the wheels at the track - the Japanese company’s involvement job does not end when the season gets underway. Enkei offer technical support when needed and wheel refurbishments throughout the year. And, critically, on the rare occasions when things go wrong Enkei investigate.

Despite the lengthy design and testing processes, wheel reliability is never 100 percent watertight. According to Furbatto the theoretical lifespan for Enkei’s wheels is approximately 3,000km. While it’s very rare for pounding over kerbs or minor off-track moments to cause issues, light collisions, stones scoring the rim and accidents all take their toll, and in practice the average lifespan is more like 2,500km.

To ensure optimum reliability, McLaren regularly carry out non-destructive tests on the wheels. But even with all this effort, it’s hard to guard against the unexpected and so wheel failures can - and do - happen. For McLaren, the most recent came at the 2008 Spanish Grand Prix, when driver Heikki Kovalainen suffered a high-speed crash linked to a manufacturing fault on his car’s left-front wheel.

“That accident was caused by a set of unfortunate circumstances - an undetectable finish had been incorrectly applied to the surface of the wheel, causing the wheel to suffer a loss of preload at racing speeds,” explains Terada. “As a result, the wheel loosened and started rubbing against the brake duct, which led to the sudden loss of tyre pressure and Heikki’s accident. It wasn’t easy to recreate that exact set of circumstances in the laboratory, but once we understood all the issues, we were able to further tighten our inspection procedure.”

Despite Enkei’s high level of Formula One involvement, it forms only a small part of their business - street wheels are their real bread and butter. But as with all things in Formula One racing, there’s an element of transfer between the track and the road that in the end helps everyone, in terms of both form and function.

“F1 wheels are certainly on the edge compared to larger runs of production wheels or lightweight after-market replacements,” concludes Terada. “From working in motorsport, we’ve learnt how to push the design of our road car wheels, making them lighter and more efficient - qualities that improve both fuel efficiency and ride quality. And while function is always the most important aspect in any motorsport, stylistically, we aim to create designs that will have an effect on after-market wheel sales.”