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Composites can be used to lower the weight of sports & leisure equipment, and bicycling is one of the fields that make the most of it. Bicycle-wheel specialist Mavic has developed an all-composite bicycle wheel that can be mass-produced. It took two years to go from prototype to marketing.
(Published on December 2007 – JEC Magazine #37)
C. GLASSEY, MARKETING MANAGER,
P. RENARD, CARBON PROCESS EXPERT, MAVIC
As a bicycle-wheel specialist, Mavic has the motivation to capitalize on its composite know-how. The company already demonstrates this in its top-of-the line products, but would like to use it more widely.
Composites in bicycling
The cycling world sets great store by any weight reduction, which can only improve performance. Since January 1, 2000, however, a bicycle must weigh at least 6.8 kg in order to comply with International Cycling Union (UCI) standards. This is to keep teams from being caught in an upward spiral of spending. It also guarantees safety and allows racers to compete on equal ground. Today, nearly all bicycle parts come in a composite version, from the frame to the handlebars, seat post, fork, brakes, derailleur, crank set, wheels, and more. Stiffness can be increased and the weight lowered by using carbon when the standard materials used are aluminium, titanium, or magnesium. Image is paramount in sports & leisure, and carbon is a dream material. There is a customer base of cycling enthusiasts who are “wacky” about weight, and for whom price considerations take second place. The price per gram for a pair of wheels can vary from three eurocents to €4.77. The lighter the wheel, the higher the price. A global carbon market estimate for the bicycle segment shows an annual consumption of 350 metric tons (MT) for forks, 300 MT for frames, and 100 MT for wheels. The “essential” part of a bicycle is its frame, which transfers load. The function of a fork is to guide direction, of course, but also to damp road vibrations. The third most important component of a bicycle consists of the wheels.
Composites and the wheel
In general, any weight saving on a bicycle’s rotating parts helps considerably to improve performance (except perhaps during very long stretches on flat ground). According to the physical principle of the moment of inertia, which needs to be reduced, the result will be most significant on the wheels, due to their large diameter. A number of small bicycle makers are already proposing ultra-light wheels all in composite. Some rare and expensive ones even have composite rims and spokes. Until now, there has been no equivalent industrial solution.
Mavic, a pioneer
Mavic is one of the pioneers in the use of composites for wheels. It has an impressive track record: according to the latest figures, 30 medals in all at the 2004 Olympic Games, including ten gold ones, and 16 medals at the 2006 World Championships, including six gold ones. We have Mavic to thank for – among other things – the first fibreglass lenticular wheel in 1973, the first carbon flat disk wheel at the 1984 Games in Los Angeles (USA), the first flat-spoke wheel at the 1996 Games in Atlanta, and the “Cosmic Carbone Pro” wheel with an all-carbon rim and metal spokes in 2005. Spoked wheels can be mass-produced but, all in all, they are “heavy”. Mavic decided to take up the challenge of producing an all-carbon wheel at the industrial level.
The “Cosmic Carbone Ultimate” wheel
In late 2004, Mavic launched the “Cosmic Carbone Ultimate” project. The goals were ambitious: to enter the select realm of wheels that weigh in at under 1,200 grams a pair by creating Mavic’s lightest aerodynamic wheel; to propose an unheardof price/performance ratio for that type of wheel; to be the first to mass-produce the wheel; and to stand out from rival products. The first prototype came out in April 2005, and others were used during the 2006 Tour de France. In the current market, the manufacturing lead times for this type of wheel made traditionally vary from 4 to 6 months. Mavic wanted to meet demand within 15 days by the time it reached “cruising” speed. The project was consistent with the idea of a line of products available to a large number of bicyclers, unlike competitor products.
For the rim, Mavic chose a one-piece sandwich structure optimized with a PMMA foam core supplied by Rohacell, and an epoxy/12k carbon prepreg skin from Hexcel. Using 12k fabric instead of the 3k that Mavic used previously was revolutionary in terms of design. The rim is not perforated, either to let the valve through (instead, an insert is moulded in) or for the unidirectional carbon-fibre spokes, which are bonded at their two ends to the hub and the rim for the front wheel. The front hub is made entirely of bondassembled carbon composite. The rear hub is in one-piece aluminium to accommodate the possibility for adjusting the tension of the dish on the opposite side of the freewheel. The mechanical performance was optimized by using only fabric for the aesthetic parts. At the risk of adding a few grams, Mavic had no desire to compromise on the basic features: rolling quality (+20g), braking quality (+10g), design (+15g), and sale-price considerations (+30g). To accommodate its choice of production capacity, Mavic developed a process that optimized the mould/press assembly and the application of pressure, with the use of a one-stage cure cycle like the one used in ski manufacturing. In 2006, the new wheel was granted type-approval in October and pilot production started in December. It entered into production in April 2007 in time to equip the racers in the 2007 Paris- Nice and Tour de France races. Since then, it has been marketed under the name of “Cosmic Carbone Ultimate” at a suggested retail price of €2,300 a pair. The pair weighs in at 1,185 g a pair, fulfilling the 1,200-g weight objective.
Composite: Mavic’s strategic choice
Mavic’s objective is to reap a long-term benefit with carbon by integrating the entire fabrication process into its French facilities and setting up a permanent technical structure.
Some parts have been outsourced previously; by not relocating, Mavic will be able to preserve and perfect its expertise. The company would like to use its development and prototyping facilities (which were launched in 2005) to become the number one composite wheel manufacturer by 2009.
It hopes to introduce a new composite wheel innovation each year until then, at which time it would be able to offer a complete line of carbon wheels.
Name: “Cosmic Carbone Ultimate”
Rim: 40-mm high-profile rim with no perforations, 12k carbon fabric with ultralight foam core
Spokes: unidirectional carbon fibre Front hub: carbon
Weight: 1,185 g (front wheel: 520 g, rear wheel: 665 g)
The goals are to lower the cost and weight of the wheels all down its carbon roadracing line, and to make its aluminium models lighter by adding the use of composites. New functions that would be impossible with metals, access to carbon products for the majority, and lower costs for the end-product through intelligent industrialization are all going to be a part of the future. Some quasi-mythical achievements to accomplish in mass production: a wheel pair that weighs only 1,000 g; a carbon wheel for cross-country bikes; or an all-carbon wheel taking a tyre and with sturdy hooks. As part of this strategy, one of Mavic’s latest achievements is the R-Sys, a wheel with tubular carbon spokes that withstand both tensile and compressive stresses to allow lower weight and greater stiffness. This new wheel weighs in at 1,355 g a pair – with an aluminium rim, more than the “Cosmic Carbone Ultimate”, but at half the price.