How did people brake a thousand years ago? The evolution of the brake system
It is said that a thousand years ago, when the ancients drove horse-drawn carriages, they essentially relied on manual effort for everything: they pumped to refuel, pulled to turn, honked with their mouths, and braked with their legs-well, the horse's legs. Eventually, after countless lessons learned through blood and tears, people realized that when going downhill, relying solely on the horse's legs not only wore out the horse but also endangered the driver.
Thus, the earliest brake system was born. People used a piece of wood as a brake pad to create friction with the wheel, providing braking force. Although the wood sometimes smoked when brakes were applied, it was enough for the slow-moving carriages. In fact, brake systems with similar structures can still be seen today. Bicycle rim brakes, for instance, have evolved from grinding the tire surface to grinding the wheel rim, but the principle remains similar.
Since the steam engine emerged in the 18th century, vehicle power shifted from human and animal to machine, and speeds increased, but braking systems saw little change. By the early 20th century, whether it was a horse-drawn carriage, a train, or an early automobile, the brake system operated similarly to those used with earlier carriages. The result? Even on flat ground, accidents still happened. Thankfully, in 1900, a genius named Wilhelm Maybach designed the first automobile drum brake. Does that sound familiar? Even today, some trucks and low-end passenger cars still use drum brakes.
Coincidentally, just two years later in 1902, another genius, Frederick William Lanchester, designed the first disc brake, which is the braking system used in more than 80% of cars today, including the Xiaomi SU7. You might think disc brakes came about much later than drum brakes, but that's not the case. Disc brakes have higher requirements for brake pad materials. Early discs were made of iron and pads made of copper, which wore out quickly. Imagine heading out on a family road trip with snacks, beer, playing cards, and three sets of brake pads-disappointing, right? So, due to limitations in material technology, disc brakes didn't become popular.
Drum brakes, however, also have their issues. Their design inherently limits heat dissipation, making them prone to thermal decay. This remains true even for modern drum brakes. But as material technology improved, disc brakes started gaining attention again. Early brake pads were made of asbestos, but asbestos had a fatal flaw: it wasn't environmentally friendly. Asbestos fibers from wear could be inhaled and cause irreversible lung damage, which is why asbestos roof tiles, once common in my childhood, are no longer used. Additionally, asbestos is a poor conductor of heat, so it was hard to cool down after the friction from braking.
Later, semi-metallic brake pads were developed, replacing asbestos with steel wool to increase hardness. But now the heat conduction was too good. The temperature rose quickly, and the brake system remained hot, causing the rubber parts, like seals and hoses, to age faster. High temperatures also vaporized water in the brake fluid, making the brakes feel soft. On top of that, metal-on-metal friction caused noise at low speeds, and the brakes rusted easily when it rained.
Due to these drawbacks, a new generation of brake pads was developed: low-metallic materials. As the name suggests, these pads had less metal content. While they weren't as durable, their braking performance was better than semi-metallic pads, and they were quieter, often used in cars that prioritize comfort. Eventually, ceramic-based brake pads emerged, utilizing ceramic fibers for reinforcement. These higher-end pads are heat-resistant, offering stable friction and reduced noise. Plus, because they lack metal, they don't leave hard-to-clean brake dust on the wheels. The downside? They're expensive.
But ceramic brakes aren't even the most expensive. There's an even higher-tier option: carbon-based brakes. These come in two varieties: carbon-ceramic and carbon-carbon. One is a composite of carbon and ceramic fibers, while the other is made entirely of carbon. Both offer excellent thermal conductivity, high-temperature resistance, strong braking force, and light weight, making them more durable. That's why carbon-based brakes are typically found on race cars, high-end sports cars, and airplanes. For everyday drivers, however, they're not really relevant due to the cost.
After all this discussion of disc brakes, you might wonder if drum brakes still have a chance of making a comeback. The answer is no-they're simply outclassed. Drum brakes are heavy, have poor heat dissipation, and are less effective at providing rapid, continuous braking. They're also not compatible with modern technology like ABS. That said, drum brakes do have their strengths. One advantage is their strong braking force. Of the two brake shoes, one follows the rotation of the brake drum while the other goes against it. When braking, the shoe that moves against the rotation creates a self-braking effect, tightening the brake as you press harder. This is a structural advantage. Drum brakes are also cost-effective, as their design hasn't required significant changes in recent years. Other than updates in friction materials, they've remained relatively inexpensive to produce.
