Improving fuel efficiency with aero-design wheels has been an area of increasing engineering attention for many years. The early results were anything but stylish, and the gains themselves were rolled into the vehicle's overall fuel-economy numbers and Cd (coefficient of drag). Now we're seeing wheel designs with quantified results announced, plus good looks.
One is a fixed design called the eVOLVE Hybrid wheel from Lacks Wheel Trim Systems (LWTS). It is a lower-cost alternative to the electronically controlled active wheel shutters just announced for the 2015 Ford F-150 (www.sae.org/mags/aei/11731). Yes, the F-150 design promises more than 2 mpg improvement in highway operation, which is huge. But the system is complex and unlikely to be as low-cost.
LWTS's eVOLVE Hybrid was exhibited at the recent Los Angeles and Detroit auto shows. Installed on a 2012 Ford Focus, a set of eVOLVE wheels was subjected to five-cycle EPA testing and improved the highway fuel-economy number by 1.1 mpg and the city number by 0.4 mpg. Almost as important: the stylish LWTS design provides a major saving in weight vs. the OE wheel and, according to the company, is much lower in cost than the premium wheels offered as options.
The LWTS design features a lightweight aluminum (forged or cast) "backbone" for a wheel assembly. The backbone itself was engineered only to carry the loads, meet durability standards, and provide the stiffness for OE driving dynamics, with no concern for styling effect or aerodynamics. Of course, that open-spoke design likely would permit a lot of turbulent airflow and not improve wheel aerodynamics. So although the backbone itself could function as the wheel and save weight, tests showed its design would not increase fuel economy, said James Ardern, LWTS Director of Business Development.
That's where Lacks' signature technology comes in—a lightweight hybrid composite aero exterior panel. The panel is glued to the aluminum backbone, and any gap between panel and the backbone is filled by an injected semi-rigid foam, creating a durable design that, with one of Lacks' stylish metallic coatings, also looks good.
On the specific design for the 2012 Ford Focus, the backbone weighs 17.4 lb (7.9 kg). The aero layer adds 1.8 lb (0.8 kg) for a total wheel weight of 19.2 lb (8.7 kg). LWTS replaced the 2012 Focus OE wheels, each of which weighs 23.7 lb (10.8 kg) with its eVOLVE Hybrid design, saving a total of 18 lb (8.2 kg).
LWTS actually designed three exterior aero panels and had wheels with them tested at the AeroDyn wind tunnel in Moorestown, NC, where most NASCAR cars are tested. The AeroDyn facility is capable of ground level measurements, specifically testing wheels, and determined that the three designs reduced aero drag by six to nine counts. The one that provided the nine-count reduction was chosen for further evaluation.
That wheel was tested to SAE J328 for radial and rotary fatigue using the GAWR (gross axle weight rating) for North America, also to SAE J175 (curb impact).
The fuel-economy numbers were derived from a combination of test track coastdown testing (performed to SAE J2263) by Roush Engineering at FT Techno's Fowlerville, MI, proving grounds, an Aisin Group operation. All Fowlerville track tests—using just the OE wheels, just the LWTS backbones, and just the eVOLVE Hybrids—were done on the same car on the same day by Roush Engineering, said LWTS's Ardern. Track work was followed by SAE J2264 testing for dynamometer simulation/adjustment, and then the EPA fuel-economy test procedures were performed.
The aero wheel is intended to be an OE product, perhaps used on specific trim levels, not a retrofit, Ardern added.
LWTS is a specialist in wheel metallic finishes, noted particularly for its chrome finishes (Chromtec bright chrome, Iridium reduced brightness chrome, and platinum matte/polish) and its Spinelle multicoat multicolor metallic.
LWTS is a business unit of Lacks Enterprises, a 52-year-old company based in Grand Rapids, MI. Originally a maker of die-cast metal parts, Lacks Enterprises switched to plastic parts in the mid-1970s. It also makes chrome-finish grilles and a range of other interior and exterior trim.