Every automaker has their recommendation but it depends on many factors. How fast your​ brakes wear largely depends on your environment, how you drive, and what kind of streets your drive on. Some general signs you​ need new brakes​ include a high-pitched squeal, vibrating brake pedal, and the car pulling to one side when braking
When the brake is applied, calipers push the pad against the wall of the rotor causing friction, which slows the car and allows it to stop smoothly. Because of this friction, the brake pads begin to wear down. If the brake pad ever wears below a quarter of an inch, it needs to be replaced.
When you let the brakes go to far the pad gets to the metal portion thus the expression "your brakes are metal to metal". At this point you won't be able to stop fast or trust the stopping distance. Next the brake pad is gone and the caliper piston starts to grind away. Now you have more expensive fix. You'll need new calipers besides the pads and rotors. When you hear constant brake grinding, you know it's dangerous.
This depends on a number of factors. Including what parts are replaced, a scheduled appointment, and available staff.
Both the front and back wheels have brakes. A car's handbrake applies the two rear brakes in a slower, less forceful way when you pull on a lever located between the front seats. A speeding car has loads of energy and, when you stop, virtually all of it is converted into heat in the brake pads.
