On a bicycle with rim brakes, looking only at the pad’s wear grooves is not enough. Inspect the surface that actually touches the rim as well. Moisture, grit and dirt are good reasons to pay closer attention to these checks; examine the rim’s braking track too.
Pads become thinner with use, but their material can also harden with age and brake less effectively. Before replacing them, identify the mounting system. Road pads, threaded-stud pads and smooth-stud pads are distinct types; some holders allow only the insert to be replaced.
Choose pads intended for your brake and rim material. Replacement also requires correct positioning and adjustment according to the manufacturer’s instructions. If braking has deteriorated or the rim’s condition is uncertain, have a bicycle workshop inspect it before the next ride.