Why Composite Back Plates Are the Future of Braking

Why Composite Back Plates Matter for Electric Vehicles

Metal-free brake pads represent a disruptive idea, but dispensing with the conventional steel backing plate offers several key advantages.

Phenolic composite backing plates have yet to gain widespread acceptance – which is surprising, given that they are up to 75% lighter, corrosion-free, thermally insulating, and possess superior damping properties. These are precisely the characteristics required for modern electric vehicle braking duty cycles.

Composite backing plates offer exactly the properties required for modern electric vehicle braking – lighter, corrosion-free, and thermally insulating.

Electric Vehicles Are Significantly Heavier

Electric vehicles are typically much heavier than their internal combustion engine (ICE) counterparts. This is largely due to the mass of battery packs, which can add up to 800 kg to a vehicle’s overall weight.

This additional mass directly affects braking system design and sizing. The increase is far from insignificant:

The Mercedes-Benz EQV luxury passenger van approaches 3 tonnes
The Audi e-tron 55 SUV, along with several other premium EVs, exceeds 2,600 kg
Even lighter, mid-range C-segment electric vehicles average almost 1,940 kg, over 600 kg heavier than equivalent ICE models

Regenerative Braking Has Changed the Role of Foundation Brakes

Regenerative braking systems are transforming the duty cycle required of foundation brakes in electric vehicles. In everyday driving, regenerative systems account for the majority of braking effort.

However, conventional foundation braking systems cannot be dispensed with. They remain essential for:

Emergency braking
Situations where battery charge exceeds approximately 80%
Providing controlled stops and parking braking

The increased mass of electric vehicles means that larger and heavier braking systems must be carried for years, despite being significantly under-utilised.

Unsprung Mass and Vehicle Efficiency

The additional weight of braking systems has a disproportionate impact on vehicle efficiency because brakes form part of the vehicle’s unsprung mass.

Heavier unsprung mass:

Negatively affects ride and handling
Requires additional suspension mass to maintain control
Reduces overall vehicle efficiency

From a vehicle design perspective, reducing unsprung mass is always desirable — yet current EV braking systems move in the opposite direction.

Carrying oversized steel braking systems that are rarely used runs counter to the efficiency goals of electric vehicles.

Brake Wear, Corrosion, and Aftermarket Implications

Reduced duty cycles will naturally lead to lower brake pad wear. While claims that brake pads will never need replacement are likely overstated, it is widely believed that corrosion will become the primary reason for pad replacement.

This mirrors current issues seen with cast iron brake discs and presents a challenge for both durability and emissions.

Euro 7 and Non-Exhaust Emissions

The proposed Euro 7 emissions standards will place greater emphasis on non-exhaust emissions (NEE), including particles released from brake wear, tyre wear, and road surface abrasion.

While exhaust emissions have been successfully reduced, NEE now represent a growing proportion of traffic-related particulate matter and are linked to human ill health. This trend is expected to continue as EV adoption increases.

Brake Wear and Iron-Rich Emissions

Brake wear is estimated to contribute up to 55% by mass of non-exhaust traffic-related emissions.

Iron, largely originating from brake discs and steel back plates, is the most abundant metal found in brake wear debris, accounting for up to 60% of metallic content. Numerous studies have identified various iron oxides across both fine and coarse particulate fractions.

As braking duty cycles reduce, corrosion products – rather than friction wear – are expected to form a higher proportion of future emissions.

The Case for Full-Composite Brake Pads

The primary sources of iron-rich emissions within braking systems are:

The friction lining
The cast iron brake disc
The 4–10 mm thick mild-steel back plates used in conventional pads

Replacing steel back plates with polymer composite alternatives offers:

Up to 75% weight reduction
Corrosion-free performance
Reduced thermal conductivity
Improved noise, vibration, and harshness (NVH) damping

A full-composite brake pad offers a corrosion-free solution while dramatically reducing unsprung mass.

Historical Barriers to Adoption

Composite backing plates have been explored previously, notably by Sumitomo Bakelite Corporation in 2012.

The primary challenge lies in retaining stiffness at elevated temperatures. Traditional phenolic composites typically exhibit a glass transition temperature (Tg) of around 150°C, beyond which the resin softens and stiffness drops.

For brake pads, this behaviour is unacceptable.

A University-Led Solution

The University of Exeter, in collaboration with a consortium of materials suppliers, brake manufacturers, and OEMs, has worked to develop a composite backing plate suitable for electric vehicle braking systems.

This innovation formed part of a four-year UK government-funded programme investigating lightweight foundation braking systems for EVs.

The solution uses a multi-layer composite structure, combining woven and unidirectional phenolic prepregs with a specially formulated phenolic sheet moulding compound (SMC) developed by FTI Group.

Testing and Validation

Prototype composite backing plates have been subjected to a wide range of industry-standard tests, including:

ECE Regulation 90 dynamometer evaluation
SAE J2522 AK Master testing
ISO 6312 shear testing
Compression testing at room and elevated temperatures
Environmental and on-vehicle testing

Shear strength exceeded R90 requirements by more than three times at room temperature, and remained double the requirement after a 400°C, 90-minute heat soak.

Thermal and NVH Benefits

Composite backing plates offer significantly lower thermal conductivity than steel, reducing heat transfer into the calliper and brake fluid. This provides an additional safeguard against brake fluid boiling during extreme duty cycles.

The inherent damping properties of composites may also help address long-standing NVH issues, offering further potential benefits.

Conclusion

As electric vehicles continue to reshape automotive engineering, braking systems must evolve to meet new challenges.

Metal-free, composite-backed brake pads offer a credible route to reducing weight, corrosion, and emissions – while maintaining the safety and performance demanded of modern braking systems.

About the Author

Dr Luke Savage
CTO & Co-founder, Tribol Braking

Dr Luke Savage is the CTO and Co-founder of Tribol Braking, bringing deep technical expertise in braking systems, friction materials, and high-temperature performance.

Luke’s career began with a PhD focused on “High Temperature Properties of Automotive Friction Materials”, and has since included managing over 20 successful Innovate UK-funded projects spanning materials science, braking technology, and automotive engineering.

The research underpinning Tribol Braking originated from one of these programmes, providing the foundation for the company’s composite brake technology. Luke continues to lead Tribol’s technical direction, ensuring every product is grounded in validated science, rigorous testing, and real-world performance.

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[4] Inokuchi, H., "Integral Molded Brake Pad with Long Fiber Thermosetting Molding Compound for Automotive Brake System," SAE Technical Paper 2012-01-1834, 2012, https://doi.org/10.4271/2012-01-1834.