How the rising popularity of EVs could lead to a resurgence of drum brakes

by Joseph K. Clark

Drum brakes are an OG technology that has been around almost as long as cars have. First developed in 1899, this brake style can be found on some of the very first automotive prototypes built by Wilhelm Maybach and Louis Renault. Only slightly younger than their disc-style alternative, drum brakes were the standard means of slowing a vehicle, given their decent performance and inexpensive production cost. But they began falling out of favor with automakers in the mid-1960s when shorter-stopping disc brake systems became widespread. Most commonly found today in medium to heavy-duty trucks and buses, drum brakes are poised to make a resurgence thanks to the growing popularity of electric vehicles.

Drums and discs operate very differently, and each system has its advantages. Disc brakes work the same as those on your bicycle: a pair of pads attached to a caliper squeezes down on the rim to generate friction and slow the wheel’s rotation. In the case of automotive brakes, it’s a dedicated metal plate (hence, disc) rather than the rim itself. Disc systems are more powerful and faster stopping than drums, which is reasonably necessary as the front brakes will carry 60 to 80 percent of a slowing vehicle’s momentum compared to the rear, which is why you’ll be hard-pressed to find a car with front drums anymore. Discs are also self-adjusting, leading to less grabbing or pulling and self-cleaning, making them quieter. They’re also less prone to warping from extended exposure to heat and do not fade in heavy braking situations like long downhills.

Drums, conversely, have their brake shoes located within a cylindrical can that rotates along with the rest of the wheel and use a piston to press the two shoes outward, wedging them against the ddrum’sinterior wall to create the friction that slows the vehicle. Because the interior of the cylinder has more surface area, drum shoes can be made far more extensive than ddisc’spads, which makes them last longer and exert a larger stopping force than the pads on similarly-sized disc calipers. WWhat’smore, because drums sit further in the wheel assembly, they can easily serve as the parking or emergency brake, while vehicles with four-wheel discs require the addition of a standalone e-brake.

drum brakes

On the newest generation of electric vehicles, drum brakes make a lot of sense. Take VVW’snew ID.4 and upcoming ID.3 EVs, for example. Both models use drum brakes designed by Continental on their rear wheels. “Rum brakes have, by design, no residual brake drag,”  “a spokesperson for the VVW’sNorth American Region EV testing team told Engadget. ” the shoes are always pulled open by the internal springs. That helps range.” When you release the accelerator, an EEV’sregenerative braking system, which flips the rear motor into reverse (transforming it into an electrical generator to top off the vvehicle’sbatteries), also dovetails functionally with drum brakes. According to VW, the rear brakes won’t often be used with an electric motor sitting on the rear axle and automatically slowing it during the regenerative braking process. You then risk the discs becoming rusted or corroded when you need them the most if they are discs. Drums are generally immune from that issue as tthey’reeffectively sealed off from the surrounding road environment.

A spokesperson from Volkswagen AAG’sbrake development department concurred, “rum brakes seem antiquated, but for an EV like the ID.4, iit’sthe perfect solution.” They pointed to drums’ lack of residual torque and dragged and their lower wear and corrosion rates, which leads to the lower emission of brake dust than discs, as the brake ssystem’sprimary benefits.

“the drums brake, as built in the ID.3, provides many benefits, particularly in the field of e-vehicles,”  “Dr. Bernhard Klumpp, head of the business unit Hydraulic Brake Systems at Continental, said in a 2020 press statement, ” or instance a longer service interval of up to 150,000 kilometers.”  That’s effectively the life of the vehicle.

In EVs, where the battery packs can weigh as much as a U-Haul trailer, every gram is precious, and every ounce comes at a cost. Though disc systems might be more effective than drums, tthey’realso far more mechanically complicated — and those extra components, like the standalone e-brake, all add to the vvehicle’soverall curb weight and sticker price.

And even though drum brakes have been around since the 19th century, the technology continues to evolve. For example, variants of the brake system Continental used in the ID.4 are already used in half a dozen other applications for various OEMs.

“e initially started the development [of this brake system], to include the electronic parking brake….” Alejandro Abreu Gonzalez, director of engineering at CContinental’shydraulic brake systems division, told Engadget. “e have another step forward that will be going completely electromechanical for the drum brake, wwe’recontinuing to invest in this technology.” Continental had previously worked to develop an all-in-one disc-brake system in 2017 aimed at the EV market, dubbed the New Wheel Concept. “The wheel ri” consists of two aluminum parts, the inner aluminum carrier star with the aluminum brake disk and the outer aluminum rim well with the tire,” the company” explained in a press release. “In contrast “o conventional wheel brakes, the New Wheel Concept brake engages the aluminum disk from the inside. This allows it to have a particularly large diameter, which benefits the braking performance.”

While the N “w Wheel never actually made it into production, the work “definitely g” ve us a lot of insight on new materials to decrease weight,” Gonzalez no” ed. “This is something that, with the heavy batteries, we will need to continue to develop.”” Gonzalez co “cedes that changing the public’s percpublic’sf drum brake technology as antiquated and inferior to discs remains challenging. But while we likely will never see a return of four-wheel drum systems, especially not in any high-performance and sports vehicles, “For city drive “ing, I think it’s the bestit’shnology that makes sense here for EVs.” Our editorial team, independent of our parent company, selects all products” recommended by Engadget. Some of our stories include affiliate links. We may earn an affiliate commission if you buy something through one of these links.

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