Ford is using carbon fibre for the wheels for
the all-new Shelby GT350R track-ready, road-going production Mustang.
In early testing with benchmark vehicles, prototype wheels showed
significant potential – improving suspension response times, chassis dynamics,
steering feel and ride quality. When the decision was made to pursue this
technology for use in a production vehicle, the engineering team was challenged
to develop a wheel that met Ford’s strict standards for durability, quality,
craftsmanship and premium finish.
Lowering overall curb weight in general is beneficial to a car’s
dynamics, but a reduction in unsprung weight (those components not supported by
the suspension) can have a significant impact on handling and performance. Less
unsprung weight helps vehicles start, stop and turn faster by reducing wheel
rotational inertia, dramatically improving response time to driver input. Lower
unsprung weight also translates to suspension components not having to work so
hard to keep the tires in contact with the road over undulating or broken
surfaces.
Although Carbon Revolution has been the leading manufacturer of carbon
fibre wheels, both Ford and the supplier recognized significant innovation was
needed to meet Shelby GT350R programme needs.
Ford sets high testing requirements for its wheels. Ford wheels must
endure tests that include curb strikes, UV and chemical exposure, and extreme
heat durability testing. The GT350R wheels would need to fulfil these demands
to proceed to production.
The durability of a carbon fibre product is a feature of the type of
resin and design intent of the part. The wheels of Shelby GT350R are designed
to be stiff, light and resilient.
One of the most severe tests for wheels in the Ford development process
involves striking a curb at speed – a test that, without proper design, can
cause serious wheel and tire damage. Because of the light weight, advanced
construction methods and resins in the wheels, along with the highly-developed
MagneRide dampers, the suspension was able to react so fast that the driver
wasn’t sure the test had been carried out correctly and ran it twice to be
sure. The suspension response was fast enough to greatly diminish the severity
of the impact – that’s the power of minimizing unsprung weight.
During track testing of the braking system, the heat developed created
rotor temperatures in excess of 900°C. As a result, the wheel design was
elevated from a road car specification to a thermal standard more suitable for
motorsports.
For decades aerospace companies have treated turbine blade materials subject
to extreme heat with ceramic coatings to help improve durability. The
technology is also used in top-tier open-wheel racing environments. A thermal
barrier coating system developed by Carbon Revolution uses this same
technology.
Carbon Revolution’s thermal barrier coating system uses a multi-stage,
multi-material coating formulation to provide a thermal barrier.
Using a plasma arc gun to liquefy a ceramic material, the wheels are
coated at critical points around the inner wheel “barrel” and on the back of
the spokes.
The result is a thin, nearly diamond-hard coating that reliably shields
the resin from heat – reducing maximum wheel temperatures and allowing
continuous track use by even the most aggressive drivers.
Also, during extreme exposure to harsh UV environments, corrosive salts
and road chemicals, it became apparent that to achieve the durability required
by Ford, a special coating would be needed to protect the resin from the
environment.
In addition, carbon fibre parts are notoriously challenging when it
comes to delivering a flawlessly smooth painted surface – the kind of finish
Ford demands for all of its vehicles.
Several proprietary new processes were developed that resulted in a
robust, high-gloss black finish that looks good and offers a long life for the
wheels.
Manufacturing carbon fibre wheels begins with the creation of the
preformed internal carbon structure, composed of precisely manufactured carbon
strands arrayed into woven fabrics. The elements are then placed into a mould
using state of the art manufacturing techniques.
An RFID chip with a unique tracking number is embedded in this
structure, and each wheel is individually entered into a quality assurance
system. Once this structure is assembled, it is infused with resin and cured at
high temperatures.
This process results in a one-piece wheel that ensures maximum strength
– eliminating the need to bond or glue the wheel’s spokes and barrel components
together.
As the wheel cures, 61 checks and over 246,000 data points are logged
before it’s released from the machine. To guarantee quality parts, the cured
wheels are analysed using a 3D computerized tomography (CT) imaging process in
which more than 18,000 X-ray images are taken.
If the wheel passes inspection, it undergoes machining for the valve
stem and mounting hardware holes before it gets painted, coated, assembled,
dimensionally checked and shipped to Flat Rock Assembly Plant for installation
on a new Shelby GT350R Mustang.
By cutting the weight of each wheel nearly in half compared to an equivalent
aluminium wheel (18lb vs 33lb), both handling and acceleration performance
experience serious benefits.
The wheels also provide a reduction in rotational inertia of more than
40 percent, which positively impacts acceleration and braking performance. The
wheels are so light, the springs and MagneRide dampers had to be recalibrated
because the suspension can respond considerably faster to road inputs.
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