All things considered, it’s better to have a car that won’t start, than one that won’t stop.

Brakes are essential, and knowing how they work – and how to tell when they need service – will help ensure your safety, and that of other people on the road.

Except in very rare circumstances, expensive brake repairs are not the result of something happening overnight. Instead, it’s because drivers put off smaller repairs or ignore warning signs, and let a minor issue grow into a major one.

It’s easiest to explain brakes by starting at the wheels. All modern cars have disc brakes on the front wheels. On the back, they will either have disc brakes or drum brakes.

Disc brakes are called that because they use heavy metal rotors that are commonly called brake discs. These are located behind the wheels. If you have alloy wheels instead of hubcaps, you can probably see them. Any time the wheels are turning, the discs are turning as well, and at the same speed.

There’s a bracket that fits over the disc, called a caliper, which contains brake pads. When you press the brake pedal, hydraulic pressure forces these pads against the disc, and that friction is what stops your vehicle. Imagine putting a pencil through the hole of a DVD, spinning the disc, and then grabbing it with your fingers to stop it. That’s basically how a disc brake works.

Drum brakes also work with friction and pressure, but with a different setup. Instead of a rotor, there’s a metal drum behind the wheel, with brake shoes inside. Press the pedal, and those shoes push out against the drum, creating the friction that stops the vehicle.

Of the two systems, disc brakes are better: they dissipate heat faster, reducing the possibility of “brake fade,” when the brakes get so hot that they don’t perform properly. But they’re also more expensive, which is why some entry-level cars still use drum brakes on the back.

Brake fluid is stored in a reservoir, located in your engine bay. On older cars, it’s a metal container with a wire closure, while on newer ones it’s made of plastic, so it’s easy to see the level. This fluid doesn’t evaporate, so if the level is low, you have a leak that should be fixed immediately.

Any time you have to add to it, you should only use fluid from a new, sealed container. Brake fluid attracts water and goes bad if it sits for a long time, even when the lid is on the bottle. Never add anything other than brake fluid: if you put in the wrong thing, it will contaminate the system, and you’ll be looking at a very expensive repair. And finally, be careful when you’re pouring, since brake fluid eats paint the way Takeru Kobayashi eats hot dogs.

Because they work using friction, brake pads wear down. Exactly how long it will take depends on each driver, because there are many variables, but the most likely one is how you drive. If you go through a lot of brake pads, look at what you’re doing. Are you rushing up at full speed to red lights, and slamming on the brakes at the last minute? And if you’re mostly doing “highway miles,” is it really straight-through driving, or are you commuting in rush hour where you’re up to speed, slamming on the brakes, and then up to speed again, over and over? If so, you’re going to wear them down faster.

If you replace your brake pads when recommended, you probably won’t need to replace the rotors as often. Have your brakes inspected regularly – at every oil change, or more if you’re doing a lot of stop-and-go driving. When needed, have them serviced, which includes lubricating the “sliders” where the caliper moves.

Every so often, open your window, turn off the stereo, and listen to your brakes. If you hear a steady squeaking that goes away when you press the brake pedal, have them inspected: that’s a wear indicator warning that your pads are getting close to replacement. If you hear a grinding or loud squealing when you hit the brakes, or if the car pulls to one side when braking, have them looked at right away.

Check them any time the brake pedal goes closer to the floor than usual when you press it, or if it feels spongy, or if a brake warning light comes on in the dash (when you don’t have the parking brake on while stopped). All of these are indications that your brakes aren’t working as well as they should.

A car that doesn’t stop, or one that stops poorly, endangers everyone on the road. Brake problems never get better by themselves. They always get worse, and that always means that the longer you leave them, the more they’ll cost.