In general, often open the city's car, brake pads will be faster than the ordinary road car fast. Because often open the city car, often to stop and go, with the brakes will be more. Take the road, it may take several tens of kilometers before the need to slow down or stop, with the opportunity to brake is relatively small.
In the case of mixed driving (half of the road, half of the urban area), the front wheel brake pads should be able to use 6,7 million km. Rear wheel brakes should be able to use more than 100,000 km. Of course this is not absolute, but has always been the experience to estimate the average.
Front wheel brake wear is faster, because the brake, the car's center of gravity will be leaning forward, the front brake to bear the power than the rear brake, the ratio is about 7: 3. So, you see the front brake disc , Generally larger than the rear brake
Add that, when the brake pads are almost expired (the remaining thickness of less than 20%), you should hear the brakes will produce "chirp" sound. This is because the brake pads on the "police hook" caused by the brake disc. Hear such a sound, it should be as soon as possible to check the following brakes.