What are the differences between bicycle hydraulic disc brakes and mechanical disc brakes in terms of performance and maintenance?

Let's put it this way, you can think of these two types of brakes as two different ways of "transmitting force."

Mechanical Disc Brakes (Cable-actuated Disc Brakes):

• Working Principle: It's very similar to the old V-brakes or C-brakes you might have had on your bike as a kid. When you squeeze the brake lever, you pull a steel cable (brake cable). This cable, at the other end, pulls a rocker arm on the caliper, and the rocker arm then pushes the brake pads against the rotor, creating friction to slow you down. It uses a "cable" to pull.
• Performance & Feel: The braking force is decent, definitely enough for daily commuting. However, because the brake cable has elasticity and can stretch, and there's friction inside the cable housing, the feel at the lever can be a bit "mushy" or indirect. You need to apply more force to get strong braking power, especially during emergency stops or long descents, which can make your fingers tired.
• Maintenance: This is its biggest advantage—simplicity! The structure is similar to old-style brakes. If you're a bit handy, you can replace and adjust the cable yourself with just a new brake cable and an Allen wrench. Even if a cable breaks on the road, any bike repair shop can fix it for you. It's very robust and has low maintenance costs.

Hydraulic Disc Brakes:

• Working Principle: This is more advanced, just like the braking principle in cars. Your brake lever acts as a small oil pump. When you squeeze it, it pushes brake fluid through a hose. This fluid, in a sealed system, transmits pressure directly to the pistons in the caliper, and the pistons then squeeze the brake pads against the rotor. It uses "oil" to push.
• Performance & Feel: This is where hydraulic brakes excel. The lever feel is very light, and you can easily generate significant braking force with just one finger. The power transfer is very direct and linear; the amount of force you apply directly translates to the braking effect, offering incredibly precise control. On long descents, your hands won't get tired, and braking performance won't significantly degrade due to temperature increases (though extreme conditions can still affect them, they're much better than cable brakes).
• Maintenance: Relatively more complex. Because it's a sealed hydraulic system, it generally requires little attention. Pad wear is automatically compensated for. However, if air gets into the system over time, or if the fluid needs to be changed (usually called "bleeding" or "flushing"), specialized tools (bleed kit, specific brake fluid – mineral oil and DOT fluid, which cannot be mixed) are required. This process can be a bit daunting for beginners, and if done incorrectly, fluid can leak everywhere. Therefore, many people choose to have this done at a bike shop.

In summary, how to choose?

• If you're a casual rider, city commuter, on a budget, or enjoy tinkering with your bike yourself, then mechanical disc brakes are perfectly adequate, and maintenance is hassle-free and inexpensive.
• If you're into mountain biking, frequently go on long rides in the mountains, or seek better performance and feel, and your budget allows, then don't hesitate—go straight for hydraulic disc brakes. The effortless, precise braking experience they offer, once you've tried it, you truly won't want to go back.

Simply put: Mechanical disc brakes are like a manual transmission—reliable, cheap, and easy to fix. Hydraulic disc brakes are like an automatic transmission—easy to use, less effort, and strong performance, but a bit more troublesome to maintain. Nowadays, most mainstream sports bicycles have adopted hydraulic disc brakes.