Carbon fibre wheels are all the rage in performance cars right now. Everyone wants that sweet, sweet weight reduction, especially when it comes to unsprung, rotating mass. But what if you’re a maker of budget performance vehicles, without the ability to drop $12,000 per car for a set of brittle, breakable wheels? When you’re banking on volume, those costs — both in construction and n warranty claims — add up quickly.
So Hyundai, for its N cars, is taking a different track. It’s working with two companies. Dymag Wheels and Hankuk Carbon, to create a semi-carbon wheel — carbon rim, metal spokes. From Dymag’s point of view, the new design should be the best of both worlds.
The manufacturer claims weight savings of 40 to 50 percent over a regular cast aluminum wheel, which would be more like five to 20 percent weight savings over a high-quality forged wheel. This may not sound all that impressive, but with wheels there’s more to consider than weight — you need to consider weight distribution, and how it affects the wheel’s moment of inertia.
When you want your wheels to change direction on a dime, moment of inertia is what really matters. It’s defined by a bunch of uninteresting equations, but the core concept is this: Given constant momentum, a rotating object will spin more quickly when its centre of mass is closer to the axis around which it’s rotating. Picture a figure skater pulling their limbs inward to speed up a spin, or the way a tall bicycle tire resists leaning over when it’s spinning.
By making the outermost part of the wheel from carbon fibre, Dymag can reduce a wheel’s moment of inertia — likely by a considerable margin, since inertia scales with radius squared — without shelling out for full carbon construction. That means better response from the front wheels when changing direction, faster acceleration and deceleration, an outsized effect from the comparatively small amount of carbon used.
How the math all shakes out on Hyundai’s new wheels is yet to be seen — we don’t yet know their size, mass, weight distribution, any of the numbers we’d need to calculate out a reduction in moment of inertia. But, behind the wheel, you likely won’t need all that math anyway. If Dymax and Hankuk got their new construction method right, you’ll feel the difference.