About Sport Bike Wheels
The wheel, the greatest achievement of early man, is equally important to the performance of today's high-powered sport bikes. Aside from providing a point where tire meets asphalt, the design of the wheel itself can provide increased maneuverability, speed and appearance. With the wide variety of aftermarket wheels available in the marketplace, choosing the right wheels depends largely on the ultimate goal for your sport bike and your personal riding style. Remember, there will always be a compromise in either function, weight, or durability, so choose wisely.
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Function
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High-performance sport bike wheels differ from standard motorcycle wheels as they generally do not employ wire spokes and accept tubeless radial tires. Motorcycle manufacturers fit wheels made from cast aluminum. These wheels are designed to accomplish several goals: to supplement the bike's geometry, reduce unsprung mass and to maximize tensile strength without added mass.
Effects of Unsprung Mass
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A motorcycle maintains stability in motion by the gyroscopic forces exerted by the spinning wheels. The wheel acts as unsprung weight, or weight that is not supported by the motorcycle's suspension, and combined with the brake rotors adds greater force to this gyroscopic effect. According to the law of physics, the heavier the wheel, the more force that is required to move or stop it. Likewise, a lighter wheel will require less force, allowing it to "turn in" quicker and accelerate faster. Two options are available to reduce the unsprung weight of the wheels: construct the wheel from lighter materials, or as Buell has done with it's Zero Torsional Load Brake system, completely re-design the wheel. As most motorcycles are not set up to use Buell's inside-out perimeter brake/wheel system, changing the material of the wheel is the best option.
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Cast Aluminum Wheels
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Cast aluminum wheels are preferred by motorcycle manufacturers and are equipped on most production sport bikes. Cast wheels are created by pouring molten aluminum alloy into a mold then allowed to cool. After cooling, excess material is removed and other elements, such as the hub and tire mount area, are machined. This process is inexpensive, largely due to cost-effective sand molds and plentiful resources. Cast aluminum wheels generally weigh between 10 to 16 lb. with a minimum of 4 to 6 mm of thickness to prevent breakage or cracking. Being fairly durable, cast wheels are designed to survive the types of conditions riders face on the road and may also be used on the race track. Typical cost for replacing a set of stock (OEM) wheels is $1,000.
Forged Aluminum Wheels
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Forged aluminum wheels offer up to a 10 percent weight reduction over OEM wheels and offer greater strength with a thickness less the 3 mm. Forged wheels are created from an aluminum alloy blank pressed into a die under extreme pressure and heat. The forging process allows the natural "grain" of the alloy to be positioned to strengthen the final product. Featuring less unsprung weight and higher strength, street riders and racers can both benefit from a set of forged wheels which generally weigh in at 8 to 13 lb. A set of wheels costs around $1,700, largely due to tremendous expense of tooling the dies for manufacturing.
Magnesium Wheels
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Magnesium, a lightweight material with almost two-thirds the density of aluminum, has been the prime choice for racers, automotive and motorcycle, for many years. Magnesium wheels are formed with the same process used for forged aluminum and can offer up to a 35 percent reduction in weight, some weighing less that 6 to 8 lb. However, magnesium does not have the tensile strength of aluminum and can break or warp easily. Race teams employing magnesium wheels replace them at least every season. For this reason, using magnesium wheels on the street is not wise, as road debris can cause serious damage, and magnesium is extremely flammable. The average set of magnesium wheels costs $4,000.
Carbon Fiber Wheels
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Used to build space shuttles and aircraft, carbon fiber is the lightest and most rigid material that sport bike wheels are made from. Because wheels are such intricately shaped items, the process to produce a carbon fiber wheel is a long and time consuming effort. With a claimed weight reduction of up to 65 percent, carbon wheels can weigh as little as 3 lb. Carbon fiber wheels are not recommended for use on the road, as the drawback to its light weight and rigidity is its lack of elasticity. Carbon fiber is so rigid that, instead of bending in an impact, it will shatter. The average set can be found for $4,500.
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- Photo Credit Kevin Roseel
