These BLACK GOLD wheels will save anything between 40-60 percent in unsprung weight, depending on their size, says Turner. But more importantly, they have much lighter rims, and carry the bulk of their weight in the metal hub. The hub has far less effect on the performance of the wheel than the rim, because of what amounts to a flywheel effect. The further the mass represented by the weight of the rim is located away from the rotating axis, the more energy it takes to accelerate it. And that energy comes directly from the bike’s engine, which is why our carbon wheels with a much lighter rim than any conventional metal wheel, even a forged magnesium one, effectively improve engine performance via easier, faster acceleration. BST claims that a standard set of 17-inch cast aluminum wheels fitted to a Yamaha R1 or Honda CBR1000RR streetbike weigh a total of 22 poundssplit 7.7 pounds for the 3.5-inch front, and 14.3 pounds for the 6.0-inch rear while a set of its carbon race wheels by contrast scales in at 11 pounds (4.6 pounds for the front, and 6.4 pounds for the rear). Halving the unsprung weight is already impressive, but because the bulk of that saving comes from the wheel’s rim and spokes, there’s an even greater saving in rotational inertia according to Turner, who claims that this is the equivalent of a five-horsepower increase when accelerating the wheels from zero to 124 mph. I discovered a dramatic drop in lap times when acting as the development rider for British wheel manufacturer Dymag in the 90s, racing that company’s prototype carbon fiber wheels before it went out of business. Just adding the carbon wheels dropped more than one second a lap on a 2.5-mile circuit on the same day with no other mechanical improvements to the motorcycle.
Back in the mid-90s Turner was living in the Netherlands and racing one of his two Ducati Supermono singles in the hotly contested European Supermono Championship run as a World Superbike support class. Carbon fiber had recently started appearing on factory Superbikes, and I was helping pay for my racing by running a company called Pro Carbon, which basically manufactured and sold many different carbon fiber parts to Joe Average, recalls Turner. I hadn’t yet got round to making a wheel. But then you showed up with the prototype Dymag carbon wheels on your Ducati Supermono, and that got me thinking. The Japanese maxi-singles like the Over Yamaha and BMR Suzuki were getting punched out to 750cc and more, and our 578cc Ducatis were struggling to keep up. So I thought, Well, we’ve got to get a bit more juice out of the bike,’ and so I took to developing the carbon wheels as a way of reducing the rotational inertia, which helped improve acceleration and countered the extra torque those big singles had over us exiting a turn. So that’s how we got started.
South Africa had already been active in developing the application of carbon fiber as a material, specifically in creating the Rooivalk (Red Kestrel’) attack helicopter with a largely carbon fiber airframe. The knowledge spun off from that project allowed Aerotek the aeronautical division of CSIR, South Africa’s government-run technological R&D; operation, whose job is to seek other applications for technical advances made in aviation design to produce a prototype carbon motorcycle wheel in 1991 in conjunction with Adept, a local wheel manufacturer. Attempts to commercialize that idea foundered when Adept went bankrupt in the mid-90s.
Gary Turner found out about the Aerotek carbon wheels, and tried to track down the remains of the project on returning to South Africa in 2000. He discovered crucial technology was still available that he was free to adopt in developing his prototype BST wheels. I wanted to make a monocoque design, but hadn’t yet worked out the technique of doing the hollow spokes, he says. Eventually I came up with the silicone idea, and then we had to get it all to work. One good thing is that composites as an engineering material offer you far more flexibility on what you want to do than any of the metals. It’s very difficult to forge or cast a piece of metal in your garage. But up to a certain point you can do a lot of experiments with laminates or composites in your home workshop, and that’s basically what I did to come up with the silicone idea. In order to create a hollow interior for less weight, Turner developed a silicone jigsaw on the inside of each spoke, over which the carbon could be wrapped and shrunk.
Meeting Terry Annecke in 2001 saw the creation of BlackStone Tek. A former IBM Systems Engineer turned marketing wiz, Annecke was headhunted by Microsoft to eventually become the U.S. software giant’s South African Marketing Director, a job she held for four years before taking a break and looking for something new. The two partners today own 75 percent of the company, although its minor shareholders include some prestigous names such as Thales, the high tech French defense contractor.
BST moved into its new home in July 2002, and the first customer BST wheels left the Johannesburg factory in October that year; production has gradually ramped up to 2000 wheels per year. Here are some of the 30 different wheel molds, in sizes ranging from a narrow 2.5-inch-wide wheel for a 125 GP bike, to an 8.0-inch-wide design statement for a custom cruiser.These are split between 30 different designs ranging in size from 16 to 21 inches in diameter and in rim sizes from a 125 GP wheel’s 2.5-inch width, up to an American power cruiser’s 8.0-inch design statement. All are built in the same way by BST’s team of skilled assemblers, around half of them women, working in two separate clean rooms with positive air pressure to ensure there’s no dust on any of the parts which might compromise the integrity of the finished product further down the line. The wheels are made from special pre-preg carbon sheet, with a combination of woven and unidirectional formats, embedded in an epoxy resin matrix with a bonding agent attached to one side of the sheet. Each BLACK GOLD BST wheel design comprises from 130 to 180 different individual carbon components, each of which must first be CNC laser-cut off the roll of pre-preg material, then individually numbered. The assemblers are provided with a full set of these parts for the type of wheel they’re building, which they then start laying up in numbered order on the half-a-wheel skeleton mold whichlike all the metal parts involved in production, including the high-precision hubs-are manufactured in-house on one of its bank of 13 CNC machines.
Each wheel is initially built in two halves, which are then joined together into a sturdy but light unit before baking. Every step of the process is logged, and the entire history of each wheel is stored with its unique serial number, which means that BST wheels can be repaired or refurbished, even in the event of crash damage or a rim damaged by a careless tire fitter. Interestingly, the carbon fiber pre-preg material must be kept cold to avoid degradation, so each new roll is flown out from the UK to South Africa packed in dry ice, then stored in a freezer room at the BST plant at -4 degrees Fahrenheit. In this temperature, the material will remain durable for up to one year—but it must be removed from there once a day and warmed to 32 degrees Fahrenheit, to keep the resins fresh.
Gary Turner’s insistence on the unitary hollow design of BST wheels, to reduce the weight in the spokes and rim without compromising strength, was made feasible by his invention of that jigsaw of specially shaped silicone intensifier inserts (originally starting as a liquid to which hardener is added) that are laid in the mold’s metal spokes, then wrapped with carbon sheet. The complete wheel is then wrapped in a special plastic bag, and baked for between four and five hours together with up to seven other wheels at a time, in one of BST’s two pressurized autoclave ovens at 257 degrees Fahrenheit and 87 psi of pressure. The silicone expands under heat and pressure to fill and shape the spokes, but then as it cools it shrinks back to less than its original size, which means the jigsaw can be extracted via the holes left in the wheel’s unstressed sections.
The cooked—as in finished— BLACK GOLD wheel is now removed from the mold and closely inspected for any visual defects, then weighed to ensure it meets specification. The rough wheel is then machined to spec and finished off, fitted with the hub unit and bearings, sprayed by a special South African-made Aer-o-Mix automotive paint which is supposedly good for fifty years of UV protection, then inspected once again. The hub is attached to the carbon wheel using a unique fastening system combining high strength aerospace fasteners with mechanical locking mechanisms, as well as high strength aerospace adhesive. All rear wheels are then fitted with an appropriate size Metzeler tire and pressure tested at 58 psi overnight, with absolutely no leakage. BST is now also making carbon fiber single-sided swingarms for the Ducati 1098 and soon MV Agusta models, including designing and making the complicated tool to wrap the carbon sheeting around it. Various other structures are continually in the works.
Here are some of the 30 different wheel molds, in sizes ranging from a narrow 2.5-inch-wide wheel for a 125 GP bike, to an 8.0-inch-wide design statement for a custom cruiser.To keep checking the validity of its manufacturing process, BST makes regular impact tests which are TV compliant, subjecting the front wheel to a 661-pound impact load, and the rear to a 1000-pound hit. We maintain our carbon wheel is much stronger as well as lighter than a forged magnesium metal wheel, says Turner. There’s also a twisting test, using special software to replicate the cyclic bending moment and applying up to 398 ft-lb of torque to the front wheel, and 443 ft-lb to a conventional rear wheel, or 516 ft-lb to an offset wheel for fitting to a single-sided Ducati/MV wheel.
BST makes a product that is rare in motorcycling, one that performs as well as it looks—and its wheels do indeed look great. Carbon fiber’s stark beauty is one that meets the criteria for both form and function, and to be able to produce a composite material wheel that is able to pass the strict TV tests while offering unrivalled performance benefits is an engineering and manufacturing feat to be proud of. We can only hope that as production techniques progress, perhaps there will be a time when carbon wheels come stock on OEM production motorcycles.
Thank you to -SR http://www.sportrider.com/ BLACK GOLD