Forget carbon-fiber wheels. What you really want mounted to your expensive sports car or track car are forged magnesium wheels.
Forget carbon-fiber wheels. What you really want mounted to your expensive sports car or track car are forged magnesium wheels.It's still rare to see forged magnesium alloys as a factory option on new cars.
Porsche is the only one to make a consistent, concerted effort to offer factory magnesium options, but it's limited to the GT cars for now. Aston Martin is making waves by offering them on the Valhalla and, surprisingly, the DBX S. Ford briefly joined the legion of magnesium when it announced the GTD with optional magnesium wheels, but no one's been able to experience them yet on account of supplier issues. That's too bad, because the technology rules.Why is magnesium so great? I phoned the founder and engineering mind behind Litespeed Racing, Patrick Warren, to dive in. Litespeed is based in California and manufactures lines of forged magnesium, forged aluminum, and carbon-fiber wheels. Its wheels are popular with race teams and used as the factory option for the Vuhl 05, a niche made-in-Mexico sports car.What it comes down to are the things you'd expect: weight, strength, comfort, flexibility, repairability, cost, and ease of production.'It is the lightest structural metal on the periodic table,' Warren begins on magnesium. 'So, where aluminum is actually very light and very strong and has very high strength-to-weight ratio, magnesium is better. It has a higher strength-to-weight ratio than aluminum. So, if you go apples to apples, your magnesium wheel is going to be a lighter, stronger wheel.'It's no surprise that magnesium is lighter and stronger than aluminum, but what might come as a shock is that forged magnesium wheels can be lighter than an equivalent carbon-fiber wheel. What!? It's true. I asked Litespeed for some direct comparisons, and a 20-inch wheel made out of magnesium ended up being about two pounds lighter than a carbon-fiber wheel of the same size. This ends up being the case because carbon fiber, as a material, simply isn't the best for the task that a wheel is meant to take on.'The advantage that magnesium has over carbon fiber is that even though carbon fiber has great strength-to-weight ratio, carbon-fiber has directional strength properties,' Warren says. 'It has really high tensile strength, incredibly high tensile strength. That means when you're pulling it. But a wheel is not necessarily under tension. A lot of times, it's under compression, or it's experiencing bending forces as opposed to pulling forces. So, even though carbon fiber is quite light, you have to build up a lot of material of the carbon fiber in order to make it strong enough to support a vehicle.'Meanwhile, magnesium has strength in all directions, particularly in bending and compressing. Carbon fiber doesn't bend. Instead, it cracks, and when it does, the wheel is ruined. Warren found that to make a carbon-fiber wheel that resists breaking as well as a magnesium wheel does when subjected to racetrack conditions, you have to use so much material that its weight balloons. It was a revelation that challenged the whole point of the company he founded over a decade ago. Their original intention was to build and sell carbon-fiber wheels as the flagship lightweight option. Litespeed still offers carbon wheels, but Warren will point enthusiasts to magnesium as the superior performance option.'I put a lot of money and time and engineering into building a functional carbon-fiber wheel,' Warren says. 'And the weight kept going up as I was going through the testing, engineering, and designing process. And by the time I got a wheel strong enough that you could use that wheel on the track, it was kind of disappointingly heavy.'That kind of logic runs counter to the growing number of cars from OEMs using carbon-fiber wheels today. Ford kicked off the industry's mainstream craze for carbon-fiber wheels with the Mustang Shelby GT350R. You'll see carbon wheels on supercars from Ferrari, McLaren, and Koenigsegg. In some ways, it's a marketing play. The visual of a carbon-fiber wheel is striking and instantly communicates performance intent. Like a carbon spoiler or splitter, it's a great way to dress up a car in a performance appearance, but similar to those ancillary parts being done in carbon, the weight savings struggle to justify the costs.I spoke to Aston Martin's vehicle performance and attributes director, Simon Newton, about what advantages forged magnesium has to see why an OEM is pursuing these wheels. Weight is obvious—the DBX S magnesium wheels save 39.9 pounds of unsprung weight versus Aston's forged aluminum wheels—but some other big results are found in steering feel and braking.'Because there's less gyroscopic effect with the technology, the net result is a much cleaner feel, particularly coming away from center in terms of steering response,' Newton says. 'The technical name for the phenomenon that it improves is hysteresis. It's when you come away from center. When you come back, the response is proportional to the amount of angle you take off. So there's no lag in the responses. You come back, it's very much more direct and consistent. . . . It just feels much cleaner and much better connected, and that really is much more significant than we all imagined when we first started on this journey with magnesium wheels.'To put some numbers to it, Aston says rotational inertia for the DBX S with its optional magnesium wheels is reduced by 25 percent in front and 27 percent in rear. Braking and perceived brake noise are also big ones for Aston. Magnesium's natural strength and density give it more structure than alternative materials, and this results in greater torsional stiffness.'It's the torsional stiffness, which helps us with NVH type of characteristics,' Newton starts. 'So, brake noises are more easily managed when you have more torsional structure. And this is definitely an improvement in our segment, where we are looking for performance and luxury refinement.'Another advantage magnesium has over the competition is in design. Take a look at the various carbon-fiber-wheel designs out there. I'd argue they're boring as hell compared with how complex and intricate forged aluminum and magnesium wheels can be. Again, it goes back to strength and durability concerns forcing design choices. Meanwhile, a forged magnesium wheel being even stronger than a forged aluminum wheel means designers can have even more freedom to play around with flashy spoke design and give us wheels that look like nothing we've seen before.'The carbon fiber, the way that you're laying the carbon fiber, you know, sheets into a mold and the mold has to be able to open, you have a lot of restrictions on the spoke geometry,' Warren says. 'So some of the carbon-fiber wheels are kind of left with design limitations.'Aston sings a similar tune, noting how much more freedom forged magnesium provides than carbon fiber.'We have more flexibility in terms of design. Because it is a forged billet, we can engineer it once, and then machine alternative face details with reasonable confidence. Whereas the carbon, you are committed to one design and the engineering associated with that,' Newton says.Ease of production is another feather in magnesium's cap. It goes hand in hand with cost. A specific set of forged magnesium-alloy wheels from Litespeed retails for about $12,500, whereas the equivalent carbon-fiber wheels are priced at about $20,000. That’s a brutal difference, and it comes down to the fact that manufacturing a forged magnesium-alloy wheel is very similar to manufacturing a forged aluminum wheel. From the extreme heat treatments involved to the massive 12,000-ton press necessary to compress the magnesium alloy into a dense structure, these processes already exist and are used for aluminum. There are some differences, though, and Warren walked me through the whole ordeal to understand how these wheels come to life.'The differences along the way, when you get your first piece of raw material before you even put it into the forging machine, the magnesium, it's really essential that you check the grain structure at that point to make sure that the grain structure is proper and there's no voids,' Warren says. 'You do like an X-ray. The magnesium, it can have a stronger tensile strength than the forged aluminum, but it's a lot more sensitive, as far as everything has to be done correctly. Where the aluminum's a little bit more forgiving.'This sensitivity to minute flaws results in needing to trash a lot more raw material than you'd need to do with aluminum, therefore increasing costs. Between more material waste and magnesium being a more expensive material than aluminum, the cost of a magnesium-alloy wheel is approximately double that of a forged aluminum wheel. Warren also notes that cutting wheels on the CNC machine requires more care when working with magnesium.'You do have to be more careful when you're cutting it,' Warren says. 'Especially when you're looking at the speeds that the CNC bit is cutting the material. You don't want to build up too much heat on the material.'That brings us to one of the hot points of the magnesium discussion. Fire! Magnesium is a highly flammable material, but nobody is selling a wheel made out of 100 percent pure magnesium. Litespeed and others sell magnesium-alloy wheels, which means there are small amounts of other materials mixed in to stabilize the magnesium and raise the flashpoint. Warren will tell you his magnesium wheels are no more likely to catch fire than aluminum-alloy wheels, and if you need any proof that magnesium alloy is safe, look to Formula 1. The wheels on F1 cars use magnesium-alloy rims, and even when a car rolls into pit lane with its brakes literally on fire, the wheels don't join the inferno.Unlike labor-intensive carbon-fiber wheels, magnesium-alloy wheels have a much brighter potential future for mass production. Warren argues it even makes sense to use magnesium wheels on nonperformance cars, particularly for EVs, due to the material's naturally excellent dampening properties that allow it to absorb small vibrations better than aluminum, therefore aiding comfort and reducing road noise. Aston's Newton agrees, noting ride comfort as one of magnesium's advantages.'If you took an aluminum wheel and you kind of flicked it with your finger,' Warren says, 'it would ring like a bell, right? The magnesium and the carbon fiber, they both don't vibrate so much, which makes them a quieter, smoother ride.'You can repair a magnesium-alloy wheel like an aluminum one too. Put a slight bend in the wheel from going off track? You can hammer it back straight and be back on the road. No need to drop another $5000 on a new wheel. Curbing one or otherwise marring the finish of the wheel can be fixed just as easily as a painted aluminum wheel needing a respray. This relatively normal fixing process is key, because you won't want to have to buy new wheels. Aston lists the magnesium wheel option for the DBX at $21,600, and while it declined to tell us how much a single replacement would cost, there's no way it would be cheap.Warren predicts more OEMs will slowly buy into magnesium as the sourcing of the raw material continually improves. Additionally, he confirmed that Litespeed will be the OEM wheel supplier for several mass-production performance cars in the near future. Ford upgrading from carbon fiber in the Shelby GT500 to magnesium in the track rat GTD is just one example of a realization in the making. It's not like magnesium is a new, unheard-of technology—cast magnesium wheels were used all the way back in the Fifties and Sixties on old muscle cars. Limited-production projects used them throughout time , but even greater production is on its way. Niche performance cars such as Porsche's GT products and Aston Martin have caught on, and I suspect it's only the beginning of a growing trend.
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