MAGNESIUM WHEELS: STRONGER, LIGHTER, A BETTER RIDE ALL AROUND
Magnesium wheels are wheels manufactured from alloys which contain mostly magnesium. Magnesium wheels are produced either by casting (where molten metal is introduced into a mold, solidifying within the mold), or by forging (where a prefabricated bar is deformed mechanically). Magnesium has several key properties that make it an attractive base metal for wheels: lightness; a high damping factor; and a high strength-to-weight ratio. Magnesium is 1.5 times less dense than aluminum, so magnesium wheels can be designed to be significantly lighter than aluminum alloy wheels, while exhibiting comparable strength.
Magnesium wheels have several distinct advantages over other types of wheels:
-- Superior benefits derived from magnesium’s light weight include a lower unsprung rotating mass in a vehicle. This facilitates faster acceleration and shorter stopping distance, better handling (particularly at turns), increased fuel economy, longer life for brakes and tires, and reduced carbon emissions
-- The high damping properties of magnesium give it the highest vibration-absorbance rate of any structural metal. This provides better shock absorption -- which increases the longevity of some vehicle components -- and a more comfortable ride. A more consistent contact patch for tire-road interaction noticeably improves vehicle performance (acceleration, braking, cornering)
-- High heat conductivity: magnesium wheels allow for faster heat dissipation, thus preventing overheating of the braking and wheel assembly systems
-- Further specific advantages exist in the case of forged wheels (see below).
Most magnesium wheels are manufactured by one of two primary production methods: casting or forging.
Cast magnesium wheelsare manufactured by the introduction of molten metal into a mold.
Taking into account their generally inferior quality compared to forged wheels, the main advantage of cast wheels is the relatively low cost of production. And although cast wheels are more affordable than forged wheels, cast wheels are designed to be heavier than forged wheels for a given required load.
Manufacturing defects found in cast wheels include cavities or porosity and a different metallurgical microstructure, entailing larger grain size. Cast wheels will tend to fracture upon overbearing high-speed impact, whereas forged wheels will tend to bend.
Forged magnesium wheelsare manufactured by mechanically deforming (forging) a prefabricated rod or bar using a powerful forging press. Several somewhat different forging techniques exist, all of them comprising a multi-step process/operation. The resultant forging is subsequently machined (lathe-turned and milled) into the final shape of a wheel by removing excess metal from the forged blank. The main disadvantage of forged wheels is the high manufacturing cost. And due to the typically high costs of finished wheels, forged wheels are still rarely purchased by non-professional drivers for regular road use.
But since forged wheels can be designed to be lighter than cast wheels for a given load, forged wheels do offer fuel economy and other distinct advantages. The forging process allows alignment of the metal fibers and optimization of the directional pattern arrangement along the spokes of a wheel. This, along with the smaller grain size, results in superior mechanical properties and performance characteristics that make forged magnesium wheels widely popular both for motor racing and with knowledgeable driving enthusiasts.
A notable disadvantage historically affecting magnesium wheels was susceptibility to corrosion. Recent improvements in magnesium surface treatment technology have largely resolved the corrosion issues -- to the extent that some manufacturers today offer a 10-year warranty.
A common misconception persists regarding the danger caused by magnesium’s flammability. But new improved alloys have been developed over the past fifty years, with no reportable incidents of magnesium wheels catching fire. In fact, the U.S. Federal Aviation Administration has conducted wide-ranging tests over the past decade, concluding that the potential flammability of magnesium is no longer a concern -- and even ruling to allow its use in aircraft cabins.
With many challenges solved by state-of-the-art technological solutions, a number of companies -- including Brembo (Marchesini), BBS, Taneisya, and SMW -- are now producing the next generation of reliable forged magnesium wheels. Additionally, several car and motorcycle manufacturers (Original Equipment Manufacturers, or OEMs) have successfully homologated forged magnesium wheels for use as original equipment.
Only a limited number of forgers in the world have the large presses required to manufacture the forgings, from which forged magnesium wheels are machined.
HISTORY AND A NEW GENERATION
The original cast magnesium wheels were made beginning in the 1930s and their production continues today, with current surface treatment technologies having solved the problems of corrosion. Some of the biggest brands producing magnesium wheels in the past include Halibrand, American Racing, Campagnolo, Cromodora, Ronal, Technomagnesio, and Watanabe. Some photographs of the original cast magnesium wheels are shown below.
Minilite Magnesium Wheels
Minilite wheels are 8-spoke design wheels, developed in 1962 for Austin Mini. Magnesium alloy was chosen for weight savings, and Minilite wheels quickly became a popular choice for racing and road use. Designed initially for a specific vehicle, the original 8-spoke pattern was subsequently extended to various sizing dimensions to accommodate a range of vehicles. Used by race teams in Europe and the United States, some sources describe Minilite wheels as “the most popular aftermarket wheel ever” and “probably the most successful competition wheel of the 1960s and 1970s.” Small-scale production of cast magnesium alloy Minilite wheels continues today.
Speedline is an established brand of light alloy wheels for OEMs, racing (single-seater and rally), and aftermarket. Some racing wheel models are made from cast magnesium alloy.
Marvic is an Italian manufacturer of alloy wheels for motorcycles, including racing team cycles. With its own in-house magnesium foundry, Marvic makes cast magnesium wheels and outsources forged magnesium wheels. The company offers wheels for vintage motorcycles and cars, including replicas of historic models, and replica Campagnolo and other wheels in original magnesium alloy.
Washi Beam Co. is a Japanese manufacturer specializing in forged automotive wheels. Founded in 1971, the company began forging aluminum road wheels in 1984 and magnesium racing wheels in 1992. The company claims to have forged more than 24,000 wheels for Formula 1 teams. The wheels for Formula 1 cars produced by Washi Beam are distributed under BBS trademark. Washi Beam also supplies numerous automotive original equipment manufacturers.
Tan-ei-sya Co. is a Japanese manufacturer of automotive alloy wheels, reportedly having an in-house forging facility. Production of magnesium forged wheels started in 1990, and the company began supplying forgings for manufacturing Formula 1 magnesium wheels in 1993. “TWS Forged” brand was launched in 2010 to establish the manufacturer's presence in the aftermarket. One-part and multi-part forged magnesium wheels are available.
SMW Engineering is the biggest Russian manufacturer of forged magnesium and aluminum wheels and wheel forgings (semi-finished). SMW supplies its wheels under private label to various automobile and motorcycle wheels manufacturers and to motorsports teams. SMW reportedly has an advanced forging process on larger presses, providing for high mechanical and performance characteristics. The company uses a special coating process and offers a long warranty on its products. SMW is also involved in forging jet parts and aircraft components.