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What are alloy wheels?
Posted on: 10/01/2014
Alright, all you wheel-geeks out there, this one is for you, so when your mate rocks up in some all-new Audi Sport Quattro Laserlight givin’ it the Big I Am, once you’ve settled back over your peanuts and lager top, you can level the playing field a little.
Are we sitting comfortably? Then I shall begin.
‘Alloy’ denotes wheels that are constructed from an alloy, that is, a combination of elements, not necessarily all metal, with either aluminium or magnesium as a base. All metals have very marked advantages for the myriad demands of today’s industries, but conversely, also weaknesses. For instance, over wood, cast iron is long lasting, far stronger and relatively cheap, however, as we all know, it’s also prone to rust and is totally inflexible. At the turn of the last century, it was discovered only by accident that by adding Chromium to steel (already an alloy of iron, by adding carbon), it stopped rusting and retained a smooth, shiny finish. Thus Stainless Steel was born.
Alloy wheels tend to be much lighter than their steel counterparts, providing better heat conduction, taking brake-generated heat away from the disks more efficiently. Lighter wheels also greatly improve the operating suspension, allowing the vehicle to more closely follow the road, thereby increasing fuel efficiency. Obviously, another benefit is they just look phat.
As with so many now mainstream aspects of car manufacture, mags started out in racing. Historically, magnesium was favoured in wheel manufacture (called ‘mags’, for reasons I can’t fathom), as the aluminium equivalents tended to be alarmingly brittle but, after a little experimentation, aluminium alloys improved markedly through the Sixties and the term ‘mags’ extended to include wheels made from many materials other than magnesium, referring more to the style than the composition.
Pure magnesium wheels were indeed very light, but are prone to pitting or corrosion and are also pretty brittle. Unalloyed magnesium is also extraordinarily flammable, if provoked. It does take quite some provocation it has to be said, but if for whatever reason, say a tyre was on fire, or the wheel rim was scraping down the road after a blow-out, the unfortunate driver might soon find themselves the unwilling owner of an incandescent brazier on one corner of their prized -and usually expensive- possession.
And this would be no ordinary fire, but a full on, ferocious, high temperature car-eating inferno, that wouldn’t be going down without a barney. It was therefore advised to watch the show from a safe distance, rather than mess about trying to douse the 3,000-degree blaze with some pocket-sized dad-can of CO2. Understandably, they quickly fell out of favour and pure magnesium isn’t used anymore, though F1 do favour mag alloys.
Unlike steel wheels, which tend to be stamped out of sheet metal, mags are die cast, gravity cast, or forged. Forging is employed only at the top end of the mag market, being as it’s so much more expensive, however, the resulting wheel is also lighter and stronger than any cast counterparts, justifying the additional cost.
All of these methods are substantially more expensive than straightforward sheet metal fabrication, but they in turn lend themselves to the boss, intricate designs we all know and love.
So. When you get outflanked by your boy’s shiny new Vorsprung purchase, get all Durch Technik on it and stick that up his pipes. You know what I mean.