“It’s time to replace the brake pad.”
Such decision didn’t come just out of a whim; it came, instead, from regular inspection of the brake pad wear. As general rule of thumb, for disk brakes, the pad needs replacement once the thickness gets below 1 mm; or, to maximize usage, just when the pad sits flush with the spring.
As tempting as it might sound, there’s a good reason mileage isn’t used as benchmark for brake pad replacement; it varies wildly, depending on brake and pad quality, the terrain we ride, and—surprisingly—our style of braking. Case on point: I had just replaced Shimano road disc front brake pad after 4,200 km, and the rear one still had considerable life left to it, while @h_rf_n replaced the similar Shimano road disc brake pad in just a touch under 1,000 km—despite the fact we rode similar routes and terrain. A small, unscientific survey to fellow cyclists revealed that average brake pads mileage for general riding is around 2,000 – 6,000 km, though trail riders and downhillers could have it as short as 500 km.
Last, but not the least; don’t wait for loss of braking power to check the brake pad wear! You could end up with bigger bills to replace the whole brake calipers—and that’s if you’re incredibly lucky. In fact, you could end up lying on the hospital bed, unable even just to slap yourself on the face for not taking time for that regular brake pad wear inspection. Or, even worse, you could end up lying six feet under the ground, never seeing your bike ever again. Yikes.