There’s no shortage of reasons for the increasing adoption of air disc brakes (ADBs) on commercial vehicles across North America: Smoother, straighter, more stable stops; longer pad life; and significantly shorter maintenance times compared to drum brakes. In fact, more than one in three North American new builds for Class 6-8 air-braked wheel-ends is now ADB-equipped. ADBs are available through all major commercial vehicle manufacturers, and in many cases, they’ve achieved standard position, reflecting both their advantages and demand.
To maximize these advantages over the life of the air disc brake, it’s important to understand the Bendix ADB friction couple – the pairing of the brake pads and rotor – and how it impacts performance, safety, and return on investment.
In technical terms, the friction couple converts the kinetic energy of the spinning rotor into heat energy by clamping the pads against the rotor, slowing the wheel-end. The contact between the pad and rotor creates friction, generating heat energy that the rotor stores and then dissipates. (One of the reasons ADBs don’t experience brake fade is that their design allows for much quicker heat dissipation than drum brakes.)
At Bendix, we’re of the mind that the best friction couples result when rotors and pads are designed and engineered specifically for each other. From the physical design and metallurgy of a rotor to the proprietary friction material in a brake pad, there are many complex variables that determine how these components will perform when they come together to bring your truck to a stop.
Determining exactly what goes into both the rotor and brake pad individually means we can engineer them to optimize torque output – the actual stopping force provided to slow the wheel-end – and wear optimally together. That second point means we design specific pads to wear at a rate with some equivalence to the rotor. This protects rotor life and helps ensure a quality friction couple. The wrong pad, for instance, may last longer but wear out the rotor faster.
Let’s Talk Rotors
Bendix manufactures two kinds of commercial vehicle rotors for its ADB22X® air disc brakes: the Splined Disc® Rotor and the conventional rotor, sometimes called the U-shaped rotor for its shape. The Splined Disc Rotor – available only from Bendix – is designed to deliver a more lightweight braking solution, and when paired with an aluminum hub, it’s the lightest ADB wheel-end combination available in North America.
The Splined Disc Rotor also incorporates a semi-floating feature to reduce thermal stresses, and it dissipates heat better than typical conventional and flat rotors, extending its service life. While the Splined Disc Rotor works well for tractors, linehaul, and pickup-and-delivery applications, the conventional U-shaped rotor is more typically utilized with standard hub configurations on straight trucks, specialty applications, or trailers.
In both cases, Bendix engineers designed the rotor to prevent coning, which occurs when more heat dissipates on one side of the rotor than the other, temporarily warping the disc. This condition can lead to uneven pad wear and cracking of the rotor – obviously impacting the life of both components. Again, though, when you have a friction couple consisting of a brake pad and rotor that were engineered together, you significantly reduce the risk of rotor coning.
Mixing-and-matching rotors and pads in the aftermarket will come at the cost of some of that optimization that’s engineered into the friction couple. It’s no accident that major North American truck manufacturers regularly incorporate a complete Bendix ADB wheel-end assembly.
Just as inferior tires reduce the effectiveness of brakes, a less-than-optimal friction couple can do the same, which in turn diminishes the ability of higher-level safety technologies like full-stability and collision mitigation. After all, what happens at the wheel-ends is just a few inches from where the rubber meets the road—an important thing to remember when selecting replacement parts for your Bendix air disc brakes.
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