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Analysis of Lightweight Carbon Fiber Wheels for New Energy
Vehicles

New Energy Vehicles Carbon Fiber Wheel Lightweight
Analysis

2023-07-11 06:59:49

Introduction
New energy vehicles are gradually replacing traditional fuel-
powered cars. The range of electric vehicles has become the
biggest development obstacle, making lightweighting
particularly important.

With the increasing demand for environmental protection and
energy efficiency, the global automotive industry is seeking
diverse lightweighting solutions. The need for weight reduction
in the unsprung mass is particularly prominent, and as an
important component of the unsprung mass, wheels account
for a significant proportion of the overall vehicle weight. One
effective way to reduce weight is through the use of carbon
fiber wheels. As raw material and manufacturing costs decrease,
carbon fiber wheels, which were once expensive and only used
in luxury or ultra-luxury models, are gradually becoming more
accessible.

Figure 1: Carbon Fiber Wheel

Application Prospects of CFRP in the Automotive Field
Carbon fiber is a lightweight, high-strength, and high-modulus
fiber material. It has a lower density than metal but is 16 times
stronger than steel. Its Young’s modulus is 2-3 times higher
than traditional glass fiber, while still maintaining the flexibility
of fibers.

Typically, aluminum alloy wheels weigh around 15 kilograms,
while carbon fiber wheels can reduce the weight to 8 kilograms,
making carbon fiber wheels a true “weight-reducing tool.”

Due to its lightweight and high-strength properties, carbon
fiber has always been a preferred material for automotive
manufacturing. In addition to wheel applications, carbon fiber
is also used in automotive drivelines, leaf springs, structures,
and bodies, ensuring sufficient strength and rigidity while
reducing the weight and energy consumption of vehicles.
According to the “2021 Automotive Carbon Fiber Market
Research Report” published by MarketaaWatch, the global
automotive carbon fiber market size reached nearly $160
million in 2020. From 2021 to 2027, the global automotive
carbon fiber market is expected to maintain a compound
annual growth rate of over 5%.

The application of carbon fiber materials in automobiles is not
only for lightweighting and energy consumption reduction but
also for improving vehicle safety performance. Compared to
traditional aluminum alloy wheels, carbon fiber wheels are
lighter, stronger, free from metal fatigue, and significantly
reduce noise. The carbon fiber wheel market in China has
enormous potential, but widespread adoption of carbon fiber
wheels is primarily dependent on cost considerations.

Figure 2: Forecast of Carbon Fiber Demand in the Automotive
Sector

With the continuous improvement and large-scale production
of carbon fiber manufacturing technology, the cost of carbon
fiber is gradually decreasing. The traditional carbon fiber
precursor is mainly made from polyacrylonitrile (PAN) raw
material, which has always been costly. However, by using
asphalt-based, polyethylene, and other materials to produce the
precursor, the cost of carbon fiber can be reduced by more
than 30%. For example, Carbon Revolution, an Australian
company, manufactures carbon fiber wheels by bonding
carbon fiber with resin, achieving large-scale production and
reducing the cost of carbon fiber wheels to a level close to
aluminum wheels.

The Chinese government has implemented relevant policies to
promote the widespread application of domestically produced
high-performance carbon fiber. In March 2021, the “14th
Five-Year Plan for National Economic and Social
Development and Long-Term Goals for 2035” was released,
which emphasized the need to strengthen the research,
development, and application of high-performance fibers such
as carbon fiber and their composites. This provides a favorable
policy environment for the technological advancement of the
carbon fiber industry in the future.

The development of new energy vehicles is unstoppable, and
carbon fiber wheels may become a standard feature in new
energy vehicles.

Comparison between CFRP Wheels and Metal Wheels:

Since the invention of automobiles in 1886, which has a history
of more than 100 years, automobile wheels have evolved from
wooden materials to modern metal materials. The commonly
used wheel materials in modern cars include steel wheels,
aluminum alloy wheels, magnesium alloy wheels, and in recent
years, carbon fiber wheels have emerged, particularly in
supercars.

Steel Wheels: Steel wheels are made primarily of iron and other
metals to enhance toughness. They have the advantages of
higher toughness, excellent impact resistance, and good load-
bearing capacity. Additionally, they are relatively inexpensive.
However, steel wheels have some drawbacks, such as
susceptibility to rust, poor heat dissipation, heavy weight, and
limitations on braking and handling.

Aluminum Alloy Wheels: Aluminum is the main component of
aluminum alloy wheels, along with elements like antimony,
silicon, and magnesium to improve overall performance. The
manufacturing process of aluminum alloy wheels is more
complex than that of steel wheels, with more processing steps.
Aluminum alloy wheels exhibit higher overall performance and
significant weight reduction. Due to the lower density of
aluminum alloy, they offer faster acceleration, better heat
dissipation, and are suitable for urban road conditions.
However, aluminum alloy wheels have relatively lower
toughness, impact resistance, and fatigue resistance, making
them unsuitable for harsh environments like off-road
conditions.

Magnesium-Aluminum Alloy Wheels: Compared to aluminum,
magnesium has a lower density and is similar to carbon fiber
composite materials. Magnesium-aluminum alloy wheels
include magnesium as the primary component, along with
aluminum, zinc, manganese, and other elements. They provide
better elasticity, faster heat dissipation, and stronger shock
absorption capabilities. They are an enhanced version of
aluminum alloy wheels in terms of toughness. However,
magnesium-aluminum alloy wheels are prone to oxidation and
have poor corrosion resistance.

Carbon Fiber Wheels: Carbon fiber wheels are a relatively new
type of wheels that have appeared in recent years. They have a
pure black appearance with a textured surface, giving them a
high-end and sophisticated look. Carbon fiber wheels offer
powerful performance, comparable weight to magnesium
wheels, high toughness, excellent impact resistance, and
corrosion and oxidation resistance. They are currently used in
motorcycles, mountain bikes, road bicycles, and automobiles.

Advantages of Carbon Fiber Composite Wheels
The wheels and tires of a car bear the entire weight and play a
crucial role in driving the vehicle under the action of the
transmission axle. As the core structural component, carbon
fiber composite wheels possess excellent load-bearing capacity
and impact resistance, delivering outstanding performance
during acceleration and under heavy loads. Additionally, carbon
fiber wheels can effectively reduce inertia and enable faster
acceleration, braking, and maneuvering due to their reduced
weight.

(1) Lighter Weight, Higher Strength

It is widely known that carbon fiber composite materials are
recognized as the best method for “lightweight” and weight
reduction in automobiles. Carbon fiber, also known as “black
gold,” is lighter than aluminum while having higher strength
than steel. It exhibits corrosion resistance and high modulus
characteristics, enabling not only weight reduction but also
strengthening of the vehicle’s structure. Data shows that a 20-
inch carbon fiber wheel weighs approximately 7.5 kg, which is
more than 25% lighter than an equivalent-sized aluminum alloy
wheel. In terms of strength, carbon fiber wheels exhibit an
overall improvement of around 30% compared to aluminum
alloy wheels.

(2) Enhanced Performance and Handling

Engineers from the Australian Carbon Revolution wheel brand
have stated that reducing the weight of a wheel by 1 kg, under
unsprung mass, is equivalent to reducing the vehicle’s overall
weight by 15 kg. For every 10% reduction in weight, the
vehicle’s acceleration performance can improve by
approximately 8%. This indicates that lightweight wheels can
provide better response to the vehicle’s power performance.
Carbon fiber wheels also offer excellent shock absorption,
increased comfort, and improved handling.

(3) Energy Efficiency and Emissions Reduction

Reducing the unsprung mass by 1 kg using carbon fiber
composite wheels is equivalent to reducing the overall vehicle
weight by 15 kg. A 10% weight reduction can result in a 6%-
8% decrease in fuel consumption and a 5% reduction in
emissions. In a scenario where vehicles use the same amount of
gasoline, a car equipped with carbon fiber wheels can travel up
to 50 km more per hour compared to a car with aluminum alloy
wheels. The weight of carbon fiber wheels is 60% lighter than
that of forged aluminum alloy wheel rims of the same size,
making vehicle weight reduction significant for environmental
purposes.

(4) Improved Handling and Superior Braking Performance

Carbon fiber wheels offer an elastic modulus of up to 200 GPa.
The higher the elastic modulus, the smaller the elastic
deformation after being subjected to forces, resulting in better
comfort and improved handling. After replacing wheels with
lightweight carbon fiber ones, the vehicle’s suspension
response speed noticeably improves, leading to faster and
smoother acceleration and enhanced braking performance.

Application Examples of Carbon Fiber Composite Wheels
Founded in 2007, Carbon Revolution is a global technology
company and Tier 1 OEM supplier that has successfully
pioneered, commercialized, and industrialized high-
performance, technologically advanced lightweight carbon fiber
wheels. In addition to luxury car wheels, the company has
announced the development of 23-inch and 24-inch carbon
fiber wheels targeting the electric truck and SUV markets. The
company is also undertaking conceptual and validation projects
for Boeing’s CH-47 Chinook helicopter wheels.

Figure 3: Carbon Revolution’s Ultra-Light Series Carbon Fiber
Wheels

The manufacturing of carbon fiber wheels requires high-
precision carbon fiber layup and high-pressure molding
techniques. Carbon Revolution holds approximately 50 patents
related to carbon fiber wheel products and manufacturing
processes and aims to improve efficiency through process
enhancements. To achieve this, the company has developed
highly automated production lines and extensively employs
machine learning and artificial intelligence technologies to
optimize the manufacturing process. On average, the wheels
are 40% to 50% lighter than standard aluminum wheels in the
market. Additionally, the wheels can be designed with
aerodynamic shapes to reduce drag and increase range without
adding weight.

Italian company Bucci Composites introduced the first 20-inch
carbon fiber wheel rim specifically designed for the
sports/supercar sector. It allows the wheel to be fixed to the
hub in a traditional way, eliminating the risk of bolt torque
loosening. This ensures that the ultra-light carbon fiber wheels
are as easy to assemble and maintain as traditional wheels. To
address the high temperatures encountered, especially when
using carbon ceramic brakes, the inner side of the wheel rim is
coated with a ceramic layer, protecting the carbon fiber and
allowing the wheel rim to be used under extreme temperatures.

Figure 4: Carbon Revolution

Bucci Composites has also equipped itself with the cutting-edge
production technology from Cannon (High-Pressure RTM-
HP-RTM), the only company in Italy that has the technology to
continue developing more wheel models for the automotive
industry.

Figure 5: Cannon’s HP-RTM Process Equipment

Cannon’s solution includes the equipment required for the
high-pressure RTM process to manufacture composite
materials with an epoxy resin matrix and carbon fiber
reinforcement:

(1) A three-component E-system high-pressure dosing unit for
epoxy resin formulation, featuring an LN10 three-component
mixing head and closed-loop control of output ratios.

(2) A short-stroke compression molding press with a clamping
force of 25,000 kN, 3.6×2.4m pressing plates, and highly
precise parallelism active control to ensure flatness of molded
parts.

Figure 6: Bucci Composites’ 20″ Carbon Fiber Wheel

Renowned British car manufacturer Bentley recently
introduced innovative all-carbon fiber wheels for its Bentley
Bentayga SUV, developed by Bucci Composites. The 22-inch
carbon fiber wheels became the largest carbon fiber wheels
ever produced, guaranteeing innovative design and exceptional
performance, while achieving a weight reduction of 6 kg per
wheel.

Figure 7: 22″ Wheels developed by Bucci for Bentley

Vision Wheel, based in the United States, has introduced a new
carbon fiber wheel developed in collaboration with IDI
Composites International and composite material weaving
expert A&P Technology. The cost of each wheel is $2,000 or
even lower.

Another American company, ESE Carbon, has launched its E2
integrated carbon fiber composite wheels in the aftermarket,
serving Tesla Model S, Tesla Model 3, and Subaru WRX STI
vehicles.

The E2 wheels utilize advanced innovative tailored fiber
placement (TFP) and high-pressure resin infusion technology,
combining performance, durability, efficiency, and innovation
with the beauty of carbon fiber, providing top-quality
aftermarket wheels.

The lighter the wheels, the lower the rotational inertia, resulting
in less force required to move the wheels forward. As a
premium carbon fiber composite wheel, the E2 significantly
reduces weight compared to aluminum and steel wheels. Tests
have shown that each wheel can save 10 pounds of weight,
resulting in a 5.3% increase in lap speed.

In simple terms, lighter objects require less work to decelerate
and stop. E2 carbon fiber wheels are 45% lighter than
equivalent steel or aluminum wheels. Tests have shown that E2
wheels can reduce braking and coasting distances from 60 mph
to 1 mile by 3.6%.

Reducing unsprung weight minimizes the forces exerted by the
suspension to keep the wheels firmly on the road. Each E2
carbon fiber wheel can reduce up to 10 pounds of unsprung
weight from the system, improving suspension performance.
The resulting improvement in tire contact leads to enhanced
steering response and more responsive handling. Whether on
the road or the track, E2 carbon fiber wheels take your driving
experience to a whole new level.

Road Testing

After years of prototype testing, E2, the most technologically
advanced automotive wheel hub ever developed, has been
created. By employing highly advanced modeling using finite
element analysis, ESE’s composite engineering team can
predict the wheel’s response in a wide range of real-world
scenarios. With this wealth of data, ESE’s wheels undergo
testing in both laboratory and field conditions, validating their
strength, safety, and performance.

Radial Impact Testing
Radial impact testing evaluates the wheel’s stability when
encountering potholes or large obstacles to prevent severe
damage or failure. Since road conditions are not always perfect,
E2 wheels have undergone rigorous testing to withstand typical
road hazards and have proven to be superior to equivalent steel
and aluminum wheels.

Curb Impact Test
The curb impact test is a crucial evaluation to assess the effects
of repeated impacts on a static surface, simulating the vehicle
hitting curbs or other fixed objects at predetermined speeds.
Even at low speeds, the contact between curbs and wheels
generates significant impact forces. E2 carbon fiber wheels
have been designed and extensively tested to withstand failures
in destructive situations such as curb impacts.

SAE J3204 Testing

The E2 has undergone comprehensive testing and is awaiting
certification under SAE J3204, a new production process for
composite material wheels. ESE is closely collaborating with
the Society of Automotive Engineers (SAE) to help establish
standards and benchmarks for composite material wheels. In
fact, ESE’s E2 carbon fiber wheels surpass the SAE’s minimum
recommendations.

Similar to metal wheels, the SAE addresses durability concerns
for composite material wheels through various fatigue and
impact tests. The SAE has also introduced new requirements to
address the unique environmental impacts of composite
materials.

Figure 11: E2 carbon fiber wheels adopted by major
automotive manufacturers worldwide.

The E2 carbon fiber wheels are designed using the latest
Tailored Fiber Placement (TFP) technology. Carbon fiber
layup has traditionally been a labor-intensive process involving
cutting and hand-molding carbon fiber fabric onto a resin
mold. This has resulted in excessive waste, and manual labor
may create bottlenecks in production.

Figure 12: Tailored Fiber Placement (TFP)

TFP achieves optimal structural performance by using
machines to arrange and stitch carbon fibers into precise
positions. This reduces layering time by 50% and material
waste by 80%. It also allows ESE to optimize the design
through precise fiber placement and orientation to
accommodate the curvature and spokes of carbon fiber wheels.
This enhances the strength and durability of the E2 carbon
fiber wheels, enabling them to efficiently manage loads and
stresses.

The E2 also utilizes a proprietary Resin Transfer Molding
(RTM) process and epoxy resin system to manufacture the
hubs, providing higher wheel rim strength and fatigue
resistance. ESE employs the highest quality, fastest-curing
resin, delivering unmatched performance at an industry-leading
Tg (glass transition) temperature of up to 212°C. The fiber-
to-resin content ratio of ESE is 60%, with a minimal void
content of 2%, making it one of the best in the industry.
Additionally, ESE can fully infuse the hub in less than 2
minutes.

Figure 13: CFRP Wheel Manufacturing using RTM Process

Conclusion:

By using carbon fiber wheels, the weight of the wheels is
significantly reduced, allowing sports cars to achieve superior
handling performance. With lower inertia, carbon fiber wheels
improve steering response and traction, resulting in faster
acceleration and braking.

Furthermore, range anxiety is a significant concern for many
potential consumers when considering the purchase of an
electric vehicle. While the driving range of an electric vehicle
primarily depends on the battery, other factors also have an
impact. Lightweight carbon fiber wheels can greatly reduce
energy consumption caused by wheel rotation during
acceleration or deceleration, maximizing the driving range of
electric vehicles.

 

January 6, 2024