Nothing transforms a car like the right set of wheels. Nothing ruins it like the wrong ones. In the same way that shoes can make or break your outfit, fitting the right set of wheels to a car makes all the difference. When manufacturers get it right, it’s no accident.
Consider the Genesis G90 and its retro-modern 19″ diamond-mesh wheels. On more plain rolling stock, the G90 would just be 5.2 metres of big sedan, quietly impressive, but not really noteworthy. On these wheels, however, it’s South Korea’s answer to the V12 Toyota Century of the late 1990s. The wheels give the car a huge dose of charisma, as their designer intended.
“From my experience teaching at ArtCenter College of Design [in California], I have had a handful of students who graduated and went on to work directly with wheel manufacturers to purely focus on designing wheels,” says John Krsteski, Chief Designer for Genesis Design North America. “In regards to wheel design at an OEM studio or in our studio specifically, all of the exterior designers are responsible for designing a wheel that compliments or fits their exterior proposal the best.”
According to Krsteski, engineers provide the designers with a list of specifications as to wheel size, width, and offset. The last is a term regarding how the wheel sits in the wheel well of a car: most factory applications are positive offset, while negative offset aftermarket rims can have a “deep-dish” look.
“Aside from designing a wheel that compliments the exterior and fits the character of the car, the strategy is simple, make all the wheel designs feel as big as possible,” Krsteski says. “The challenge is always how to make the smallest wheel [outside diameter] feel bigger and look as good as the larger wells. Once we’ve narrowed down from several dozen proposals, we’ll develop them in 3D digitally and proof check them by 3D printing the designs and putting them on the physical model for further evaluation and design refinement.”
It seems odd to suggest the G90′s wheels are only nineteen inches in diameter, but they aren’t particularly large by modern standards. European luxury marques often top out at twenty inches on sedans, and crossovers require even larger wheels to fill out the wheel wells. Genesis’ team has done well to make a significant impact with the space they had to work in. Big wheels might look cool, but they come at a cost.
That cost is called unsprung weight, and to come back to our shoe analogy, I must ask you to picture a prima ballerina about to perform Swan Lake. Now, picture her in lead-soled diving boots instead of ballet flats. The performance will be less than elegant.
Heavy wheels are the same. Weight inboard of the suspension can be controlled through spring rates and damping. Weight that’s hanging off the suspension can make a vehicle’s ride crash over bumps and react poorly to cornering. The original alloy wheels, those developed by aftermarket companies like Minilite in the UK in the 1960s, were a solution to the poor performance of steel wheels.
“Manufacturing wise, the creativity threshold is widening as we look to light weight and multi-piece wheels that offer greater aero performance,” Krsteski says. “With lightweight, strength, and performance being the collective goal, engineering and design are working more closely together to optimize the design that provides the most efficient gains in all areas.”
Let’s look at an effort from a company that competes in the fiercest arena of motorsport: F1. Mercedes-Benz has a dominant record in the field, and are bringing some of that racing technology to the road with their upcoming Mercedes-AMG One. It’ll have more than a thousand horsepower, be capable of top speeds above 350 km/h, and have the lightweight agility of a hummingbird. It’s also going to need some wheels.
Mercedes-AMG recently released a German-language walkthrough of their various wheel offerings. Some of the details pointed out were surprising – a prototype carbonfibre wheel was actually heavier than the standard alloy wheels. Some elements were common sense, with the amount of metal used in the aesthetics of a wheel drastically affecting weight.
However, Mercedes has come up with all sorts of engineering trickery to keep weight low. Take a look at the big boots on the AMG GLS63. They are a staggering 23 inches in diameter, a huge swath of black-faced metal. These wheels should be like tiny moons, ruining the ride, right?
Again, there’s a bit of retro-modern heritage going on here. The Monoblock style of wheel dates back to the 1980s, when it was a signature part of the way AMGs looked. This modern version is a forged alloy, which is stronger than ordinary cast metal. Depending on the duty requirements, Mercedes-AMG can get away with a little thinner metal with a forged rim, which help keeps weight in check.
As at Genesis, engineering and design work hand in hand. Using computer modelling, engineers were able to reduce material while maintaining strength. The AMG-One’s wheels are made from forged magnesium, which helps keep weight down further. Almost 80mm wider than a standard AMG wheel, they still weight just 8kg.
With more ordinary cars, designers aren’t chasing performance this extreme. Krsteski points out that manufacturers often fit new wheels as a way of refreshing the look of a car mid-cycle through its lifespan.
That’s something you can, of course, do yourself, which is why the aftermarket industry exists. However, before you pull off the set of wheels that came on your car from the factory, spare a moment to think about the designer that fitted them on there. Take heed of the dangers of adding too much unsprung weight by fitting a larger wheel, and consider whether the extra cost of a stronger forged wheel is actually worth it. Don’t forget to consider the cost of replacement tires.
Wheels can make the car. They can make a statement. Manufacturers spend a lot of time and money getting it right, so tread carefully. And watch out for those curbs.