cxwrench

There is absolutely NO mileage number at which you should replace your pads. It is totally dependent on your individual riding style, your body weight, and how you maintain your bike. Some people tear through rear pads because they're afraid to use the front brake. Some people tear through pads because they live in a wet climate and that wears pads much quicker than a dry climate. Look at a photo of some brake pads...you'll see the backing plate and the friction material. It starts out about 3mm thick. When the friction material gets down to 1mm you should start thinking about replacing them soon. You could have this much wear in a 1 hour wet/muddy CX race or if you live in AZ they could last a year. Check them often. You can look through the caliper or you can look through the opening in the top of the caliper.

When you adjust for wear do NOT use the barrel adjusters, ONLY adjust with the adjustable inner piston and adjusting the caliper position.