Stopping Power: A Primer on Automotive Brakes
Brakes are relatively simple, but advancements remain to come.
Researchers have been unable to pinpoint the precise calendar origin of automotive brakes, but the best evidence suggests the Stone Age, which spans nearly 3.5 million years. Fortunately, a series of 166 22-minute animated documentaries that aired on national television from 1960 to 1966 provided a detailed account of how those first automotive brakes worked.
The series spotlighted the daily life of Fred Flintstone, the primary driver, who—en route to and from his daily job at Slate Rock and Gravel—drove an open-air, open-floor four-passenger vehicle that used large rolling cylindrical rocks front and rear. When he needed to stop, Flintstone simply lowered his heels to the ground, and the car halted, often in a cloud of dust and frequently preceded or followed by a call of "Yabba dabba doo!" Decades of linguists have been unable to accurately translate this, but it could be taken to mean, "Ouch! When is someone going to invent an automotive brake that doesn't take skin off of my feet?"
Fast-forward a million years or two, and Flintstone's cry was answered by the rudimentary efforts of buggy and wagon manufacturers, who applied wooden blocks to rub against the wood or steel wheels to help them slow down, when the exclamation of "Whoa!" was ignored by the horses, oxen, donkeys, or mules. Once vehicles, both towed and motorized, began using rubber tires, the practice of rubbing wood against them did not prolong already unimpressive tire life. So leather replaced wood, which still did not result in sufficient 60-to-0-mph stopping performance. Something entirely new was called for, and it came from a variety of inventors with a variety of solutions in a variety of countries.
There are two basic kinds of modern brakes: drum brakes and disc brakes. While we tend to think of discs as a much more modern development, both types were being actively developed around 1900. The U.S. market embraced drum brakes and didn't really shift to discs until well after Europeans discovered their basic goodness.
Both kinds are exceedingly simple. Generations of enthusiasts have explained discs to civilians by pinching a dinner plate between thumb and forefinger; they have explained drums by rubbing their hands together. One advantage of discs is the fact they're especially effective in wet weather—the pads, or pinchers, clear away water on the discs easily and immediately. Drums—especially on the front of a 1972 Suzuki Titan motorcycle, as we learned to our detriment decades ago—can get water caught in the brake that doesn't drain off, creating rust. That's an extreme example, but it didn't seem that extreme when we once barreled through an intersection with only the sad little rear brake to slow us. Exciting!
Antilock systems, which really began to proliferate in the '70s, allow a vehicle's wheels to roll slightly by pulsing the application of the brakes even as you apply full braking power and thus prevent dangerous skids; they also allow you to steer the vehicle at the same time. But other than that, "In the last 50 years," says Dan Sandberg, president and CEO of Brembo Brakes North America, "you can argue there was not that much [else] going on."
Alternative materials, especially those that provide lighter weight, have been investigated successfully and include everything from aluminum to carbon, with one notable difference in design to those from years ago: "Now we use a fixed caliper—the part that houses the brake pads and pinches the discs—instead of a floating caliper." A floating caliper can slide left and right via pins and bushings on the bracket; a piston on the inner side of the disc pushes its brake pad, and the force moves the sliding caliper into another brake pad on the opposite side of the disc. A fixed caliper uses a solid mount, and there's a piston (or pistons) on both sides of the disc that can pinch the disc more efficiently and effectively.
Brembo, though based in Italy, has ultramodern factories in North America, including one in Monterrey, Mexico, and one in Homer, Michigan. And the company is building a foundry near its Michigan plant, "and nobody builds foundries anymore," Sandberg points out. It has been a challenge, but a rewarding one, to navigate all the federal, state, and local requirements for building a "dinosaur-era" factory.
Of course, brakes are not what actually stop a car. That responsibility falls on the tires, and the industry has seen bigger and better tires and wheels, along with a corresponding rise in horsepower. And despite the use of lighter materials in every aspect of automotive design, we've actually seen overall vehicle weights rise, in the sense that trucks and SUVs, such as the 707-horsepower Jeep Grand Cherokee Trackhawk, are now considered in some cases high-performance vehicles. Such an SUV can accelerate from 0 to 60 mph in less than 4.0 seconds but weighs more than 5,000 pounds. Add to that the towing capacity of many trucks and big SUVs that can top 10,000 pounds, and high-performance brakes take on a new meaning and a new role.
Many of the improvements in brakes are traceable to what manufacturers have learned on racetracks, participating in motorsports that involve two and four wheels. Manufacturers talk a lot about "tech transfer," often as a way to justify their investment in racing. And indeed, motorsports has led the way in developments such as optimizing fuel usage, in terms of both power and miles per gallon. Racing has provided a way to test lightweight materials such as carbon fiber under extreme conditions and to develop even legacy materials like aluminum to increasingly sophisticated degrees. But nothing we use on our daily-driver cars and motorcycles has benefited more than brakes.
Again, much of that technology has been developed and proven by Brembo and AP Racing, a Brembo subsidiary. For more than 50 years, U.K.-based APR has invented and built brakes and high-performance clutches used in a variety of series. APR is heavily into NASCAR, and its products are used on quite a few racing sports cars, such as Chevrolet's Corvette Racing team. AP brakes were used on the championship-winning cars of 2018 NASCAR Cup champion Joey Logano and NASCAR Xfinity champ Tyler Reddick.
Indeed, Brembo and AP Racing are perhaps the most dominant brands of brakes used in NASCAR, Formula 1, Formula 3, IMSA, the FIA World Endurance Championship, the World Touring Car Championship, and MotoGP. Brembo is the only brake used on Formula E cars. Meanwhile, in 2018 APR supplied brakes, clutches, or both to more than 30 champions across the spectrum of the motorsports world. Last season at the Japanese Grand Prix, Brembo scored its 400th F1 win.
One of the biggest problems facing high-performance brakes, Sandberg says, isn't on-road or on-track performance but rather counterfeiting. AP Racing, for example, sent out a warning in December with two photos of what appear to be its calipers, one red, one silver, that said: "AP Racing has found some calipers which we have not manufactured with our brand name etched/machined on the product in the market." Brembo has also been so victimized by cheap knockoffs, as have other quality builders.
In the past, one way to tell the difference has been that the real logos are burned into the calipers by etching or machining, not just printed on. This latest development suggests forgers have become more sophisticated. When in doubt, check with the manufacturer before spending your money, because there's no warranty, no guarantee, and no return credit available on fake products.
Brake development will continue, with near-future improvements targeted at the inevitable self-driving autonomous industry, but for those who prefer to brake for themselves, you'll still have options.
"Brakes will move down in size," Sandberg says, and increase their dependence on sensors that allow for complete brake-by-wire, which could be entirely electric or electric-and-hydraulic hybridized. Carbon brakes and carbon-fiber elements will increase in usage, but steel works too well for the money to be phased out anytime soon from passenger and industrial disc construction. The same goes for floating calipers, especially on low-cost installations on lower-performance cars.
Perhaps more interesting to enthusiasts and available initially on the OEM level: the ability to customize things such as brake feel, pedal travel, and pedal firmness. Such offerings should arrive within a few years, migrating quickly to aftermarket kits. Firm pedal, soft pedal, changing those parameters depending on the road, the weather, your speed—it's all on the way. As Sandberg says, brakes may be simple, but research regarding their design, operation, construction, and even their appearance is nowhere near complete. To which we say: Yabba dabba doo.
LEFT: Brembo's Extrema caliper is used on extreme performance cars, in this case the Ferrari LaFerrari. The Extrema is a monobloc aluminum caliper, this one from the car's rear end and featuring an integrated electronic parking brake. CENTER: Carbon-ceramic brake discs are less than half the weight of equivalent cast-iron discs, and they look good, too. Additionally, they offer benefits such as producing less brake dust and providing better corrosion resistance. RIGHT: This caliper, the B-M8, is designed for the front brake systems of trucks, SUVs, and large high-performance sedans. It's one of the largest calipers Brembo makes, measuring 15.5 x 7.0 x 5.5 inches. Seen next to it is one of the brake pistons, which pushes the pads against the disc.
Reinventing Venting: For years, Brembo has worked on the shape of its disc ventilation chambers. One of the first results was development of the PVT (Pillar Venting Technology) ventilation system, which extended disc life.
Differing Designs: New ventilation systems like Star Pillar (left) and Comet Pillar (center) further improved fluid dynamics and resistance to cracks.
1. GT caliper: Six-piston monobloc used in road racing, endurance, and sprint applications. 2. Corvette ZR1: Six-piston monobloc aluminum; low weight and high stiffness provide a firm pedal feel. 3. GT-S: Six-piston; properties gleaned from the caliper that helped the Ford GT win the 24 Hours of Le Mans. 4. B-M8: Eight-piston aluminum monobloc; designed for trucks, SUVs, and sedans. 5. B-M4: Four-piston aluminum monobloc; features a radial-mount design and internal fluid passages. 6. B-M6: Six-piston aluminum monobloc; designed for a range of front applications.