Drum brake pads are generally recommended to be replaced every 60000 kilometers of driving. The situation for determining whether brake pads need to be replaced is as follows:

1. Usually, a pair of new brake pads have a thickness of about 1.5cm. If the thickness of the brake pads is less than 0.5cm, replacement needs to be considered.

2. If there is a sound of "iron rubbing iron" during braking (which may also be due to the grinding effect of the brake pads during initial installation), the brake pads must be replaced immediately.

3. The braking effect is significantly weakened and the brake pads need to be replaced in a timely manner.

The specific tutorial for replacing drum brake pads is as follows:

1. Remove the rear brake drum.

2. Remove the return spring.

3. Remove the fixing screw.

4. Remove the front and rear brake pads.

5. Install new brake pads.

6. Adjust the height of the handbrake.

7. Install brake drum.