Bike brake pad wear: when to replace and how to check

Brake pads: the fastest-wearing part of your braking system

A new pad is roughly 4 mm thick total: ~3 mm of friction material on a ~1 mm metal backing plate. Once you have less than 0.5 mm of friction left (about 1.5 mm overall, the threshold Shimano and SRAM both call out), what's biting is essentially the backing plate. On disc, that turns a 20 EUR pair of pads into a 40 EUR rotor. On rim brakes, it's the rim itself you're trashing.

Disc or rim: two completely different jobs

Before talking wear, you need to know what you're looking at. The two systems share almost nothing maintenance-wise.

• Rim brakes (V-brake, caliper): rubber pad or cartridge that grips the side of the rim. The rim is the braking surface - a worn rim has to be replaced, and that means a new wheel.
• Disc brakes: pad inside a caliper that squeezes a rotor bolted to the hub. The wearing surface is the rotor, replaced independently from the wheel.

On disc brakes, three pad families based on friction material: organic (resin), sintered (metallic), and semi-metallic. Organic bites fast cold, runs quiet, but wears faster and dislikes long-descent heat. Sintered lasts longer and handles heat well, but it's louder and needs to warm up to bite. Semi-metallic splits the difference. For city or road use, organic is fine. For aggressive MTB, loaded gravel, or long descents, semi or sintered are safer.

Minimum thickness: when you're in the red

No "replace when it feels off". Three concrete criteria, to check visually each time you clean the bike.

• Disc: 0.5 mm of friction material minimum, which means a total pad thickness around 1.5 mm including the backing (Shimano/SRAM threshold, sometimes engraved on the side). Below that, replace. Use a caliper or eyeball it through the gap between the caliper bridges.
• Rim: wear indicator. Most pads have a witness groove moulded into the rubber. Once it disappears, you're done. On pads without an indicator, replace when the thinnest spot drops below ~1 mm.
• Contamination: chain oil, grease, degreaser, leaked brake fluid. A soaked pad can't be cleaned (the term is "glazed in") - replace, no negotiation.

On disc brakes, also check the rotor thickness itself - a separate measurement from the pad. The minimum is usually engraved on the rotor (1.5 mm for Shimano, 1.55 mm for SRAM). Below that, the rotor overheats and warps, so it gets replaced too.

Symptoms that should put you on alert

Before reaching for the calipers, there's usually a warning sign. Four typical ones.

• High-pitched noise (squeal, whistle): can come from glazing, contamination, or a worn pad scraping metal. Not always a wear sign, but worth a look.
• Loss of bite: lever pulls further for the same braking, stopping distance grows. If the pads look fine, check for glazing or contamination before swapping.
• Glazing: the friction surface becomes smooth and shiny, like vitrified. Often after a long descent with continuous braking. A pass of fine sandpaper can rescue the pad - otherwise, replace.
• Vibration under braking: warped rotor, uneven pads, or a poorly torqued caliper. Pull it apart and inspect before ordering anything.

Replacing your pads, step by step

Disc or rim, expect 20 to 30 minutes. The final bedding-in is not optional.

1. 1

   Identify the right model

   On disc, each brand has its own shape (Shimano B01S, G02S, L02A… SRAM, Magura, Hope, TRP). A photo of the old pad or the part number stamped on the side. On rim brakes, V-brake and caliper pads aren't interchangeable.

2. 2

   Drop the wheel and pull the old pads

   On disc: remove the retaining pin or clip, then the old pair with its spring. On rim: open the brake and undo the pad nut.

3. 3

   Push the pistons back (disc)

   Before inserting the new pads, push the pistons fully back into the caliper with a piston press or a flat screwdriver pressed on the old pad.

   TipOn rim brakes, aim for about 1 mm of toe-in at the front and check the pad hits the rim square, never biting the tyre.
4. 4

   Fit the new pads

   Slide the new pair in with its spring, replace the pin (disc) or re-tighten the nut (rim). Never touch the friction material with your fingers and keep all degreaser away.

5. 5

   Re-seat the pistons (disc)

   Pump the lever 5 to 10 times to bring the pistons back against the pads - it's normal to feel soft on the first pulls. If it stays soft after that, it's most likely a bleed issue.

6. 6

   Bed in the pads

   30 to 40 progressive stops on the flat: build to 25-30 km/h, slow to ~10 km/h without stopping. This lays a transfer layer onto the rotor or rim. Skip it and the bite stays weak with a higher risk of glazing.

What we see on ChainLog

From our current user base - still small - pads are one of the components with the widest spread. Lifespan depends as much on riding style and weather as on the pad type itself.

Some early ranges we're seeing:

• Organic disc pads on dry road: often 2,000 to 4,000 km, sometimes more for lighter riders who use the brakes sparingly.
• Sintered or semi pads on MTB/gravel: 1,500 to 3,500 km, but it can drop to 500 km through a muddy winter.
• Rim pads on dry road: 3,000 to 8,000 km, divided by 3 or 4 as soon as you ride regularly in the rain.

These are early observations (likely selection bias - ChainLog users are probably more maintenance-conscious than average). Use them as a reference point, not a rule. The minimum thickness check still wins.

Automatic tracking, so you don't get caught out

Pads are the classic part you forget to check. They wear slowly, you adapt to a braking that's getting weaker, and you notice the day you hear metal on rotor.

ChainLog tracks kilometres per component and alerts you before that point. Not as a replacement for the visual check - minimum thickness is still what counts - but as a reminder to actually look.

Not a perfect measurement. Just a regular nudge, enough to never score a rotor by mistake.