Game Changer: The alloy wheel

Like a lot of materials available to the motor industry, magnesium is pretty dangerous stuff. Over many years though, its wilder nature was tamed and the lightweight metal became integral to production of engine blocks, transmission casings and wheels.

Magnesium, or ‘elektron’ as it was also known, had been used commercially since the 19th Century and for automotive components since the 1920s.

When Ferdinand Porsche designed the German 'People’s Car', he specified that to save weight the engine crankcases in his Volkswagen 'Beetle' would be made from magnesium alloy.

Before and since that time, magnesium has been used in numerous vehicles and for a wide variety of purposes, but most commonly in the manufacture of lightweight wheels.

Competition vehicles in particular need wheels that are strong enough to resist cornering forces and road obstacles but light enough to reduce unsprung weight. Wheels made from almost pure magnesium fulfilled both criteria but were a liability when a crash occurred.

The combination of spilt fuel or oil, hot components and magnesium created fires that burned with intense heat and could not be extinguished with water or any conventional fire-fighting technique.

The only effective way to extinguish a magnesium fire was to bury the burning components and not many racetrack crash crews had access to dump trucks full of sand.

One magnesium fire that prompted immediate changes to the use of the material occurred at Le Mans in 1955, when a Mercedes-Benz with light alloy bodywork collided with an Austin-Healey and burned for over an hour.

British company Magnesium Elektron Ltd had during the 1930s become a leading source of magnesium components for aircraft. After World War II it diversified and began supplying cast magnesium alloy wheels to manufacturers of racing and road cars.

Prominent among them were Lotus and Cooper, both of which used wheels with high proportions of magnesium, until the point where they began to fracture under the intense lateral loads generated by wider tyres.

In the USA, Ted Halibrand learned about magnesium while serving with the US Air Force during WWII and in 1946 established a business making sand-cast magnesium wheels for Indy racers.

The business grew rapidly and by the 1960s, Halibrand’s ‘pin-drive’ alloy wheels were being used on cars like the Le Mans Ford GT40 and Shelby Cobra.

Some early low-cost wheels combined a steel rim with an alloy centre and spokes with the components riveted together. These wheels could not be used with tubeless tyres because they would not hold air and after some years the rivets could fail as well.

As technology progressed the quantity of volatile magnesium used in wheel production was reduced. Today’s ‘mag’ wheels, which are now pretty much standard on all new models except some entry-level cars and commercials, are made primarily from aluminium.

One that used magnesium alloy to great effect was the ‘Minilite’ wheel developed for competition use by BMC Minis. These wheels were distinguished by eight short, rounded spokes on a polished or black enamelled rim.

Wheels of different sizes front to rear became popular during the 1970s and gave rise to the three-piece ‘composite’ rim. These are frequently fitted to high-performance muscle cars and their derivatives used for competition. However, they weren’t invincible.

One famous and public failure occurred during the 1982 Bathurst 1000 when previous winner Kevin Bartlett slid his Chevrolet Camaro to a stop on its roof after a composite wheel failed and caused a rear tyre to deflate.

The safety of some aftermarket alloy wheels also came into question in 2015, when one example failed during real-world testing by the Federal Chamber of Automotive Industries, GM Holden and Mercedes-Benz Australian at the Lang Lang proving ground.

And now carbon-fibre wheels have emerged as the most advanced wheel construction type for high-performance vehicles such as the Chevrolet Corvette Z06, supplied by Carbon Revolution in Geelong.