Bike Brake Pads: When to Replace Them, and Which Ones Fit

Brake pads are the cheapest safety-critical part on a bicycle. A set costs less than a takeaway, takes about fifteen minutes to fit, and is the only component on the bike that is designed to wear away to nothing.

They are also the part nobody checks, because a worn pad does not announce itself. Braking gets slightly worse every week, you adapt to it without noticing, and the first real signal arrives on a wet descent when you need the brake to do something it can no longer do.

The thing that catches everyone out

A brake pad fits a caliper, not a bike. There is no such thing as “brake pads for a road bike”. If you search that, you will be shown a dozen shapes that fit a dozen different calipers, and roughly eleven of them will not fit yours.

The first split is the obvious one. Rim brakes squeeze a block against the side of the wheel; disc brakes squeeze a small pad against a metal rotor at the hub. These are unrelated parts that share a name. On this site the Tommaso Imola and Monza brake on the rim, and the Sentiero and Sterrata use discs, so two bikes from the same brand take completely different parts.

The second split is the one that actually costs people money, and it is inside the disc category. Shimano use one pad family for their mountain-bike-derived calipers — B01S and its relatives, which is what most budget disc bikes are built around — and a different family entirely, the L series, for the flat-mount road and gravel calipers on groupsets like GRX and 105. Both are “Shimano disc pads”. Neither fits the other.

When rim pads are done

Park Tool group rim pads into three systems — road, threaded stud and smooth stud — and note that with use, pads simply lose material until they are too thin to be effective.

There are three signals, in the order you will notice them:

1. The wear grooves have gone. Most rim pads have shallow grooves molded into the braking surface. They exist as a wear gauge and nothing else. When you can no longer see them, the pad is finished.
2. The pad has hardened. Park Tool make the point explicitly: pad material hardens as it ages as well as wearing thin. A shiny, glazed pad with plenty of material left can still stop badly, and old stock that has sat in a shed for five years is worth replacing on age alone.
3. There is grit embedded in the surface. Look closely. Small bright specks are aluminum filings and grit that have been pressed into the rubber, and they will machine the braking surface off your rim. That is a wheel, not a pad, so this one is worth catching early.

When disc pads are done

Disc pads get an actual published number, which is a relief. Park Tool’s stated threshold is that the pad material should measure at least 1mm thick. Below that, replace them.

That 1mm is the friction material only — the gritty layer — not the metal backing plate it is bonded to. New pads carry somewhere around 3mm to 4mm of material depending on the shape, so 1mm is close to the end rather than a comfortable margin.

Look into the caliper from above with the wheel in place, or take the wheel out and look straight through it. If you cannot tell, pull the pads: on most calipers that is one retaining pin or bolt and thirty seconds of work.

One thing to check while they are out: if the two pads have worn unevenly, the caliper is not centered. Fix that first — the brake adjustment guide covers centering — or the new pads will wear exactly the same way.

Compounds, in plain English

Disc pads: resin, semi-metallic, metallic

Park Tool publish a straight comparison of the three, and it is refreshingly free of marketing:

• Organic (resin). Best initial bite, and best for rotor longevity. Poorest durability in the wet.
• Semi-metallic. Middle ground on every measure.
• Metallic (sintered). Longest pad life in the dry. Generates more brake noise.

For a first bike ridden on roads and dry gravel, resin is the sensible default: it bites well from cold, it is quiet, and it is kind to the rotor. Move to semi-metallic if you commute through winter or live somewhere with long descents, where the wet durability matters more than the silence.

Park Tool also warn that there can be compatibility issues between certain rotor materials and pad materials — some rotors are marked resin-only. If yours has writing on it, read it before you buy metallic pads.

Rim pads: it is mostly about rain

Kool Stop publish descriptions of every compound they sell, which makes them one of the few places you can get a straight answer. Their salmon compound is described as an aggressive compound for extreme all-weather conditions, especially in the wet, but still superb in the dry. Their black is the standard compound, great in all weather but designed for dry-condition riding.

That is the whole decision. Wet-weather rim braking is genuinely poor — it is the main honest argument for buying discs instead — and a softer all-weather compound is the cheapest way to claw some of it back on a bike you already own. The trade is wear rate: softer pads in worse weather do not last as long.

The one hard rule: aluminum rims and carbon rims take different pads. A pad meant for an alloy braking surface will destroy a carbon one. Every bike we recommend has alloy rims, so this is unlikely to bite you here, but it is worth knowing before you buy a wheel upgrade.

How to work out which pad you need

Three steps, in this order, and do not skip the first one:

1. Take the old pad out and look at it. This is the only reliable method. Most pads have a part number stamped or molded into the backing plate. If yours does, that number is your answer and you can stop here.
2. If there is no number, measure it. Length, width and thickness of the backing plate. Good listings publish these — the resin pads above state 30.5 x 35 x 4mm — and matching three numbers is far more reliable than matching a photograph.
3. Check the caliper name against the listing. Sellers of multi-fit pads list the calipers they are cut for. Your caliper usually has its model printed on it. If your caliper is not on the list, believe the list.

If the bike is still boxed or newly built, the manual has the pad specification in it. That is the easy version of all of the above, and it is the one moment in the bike’s life when the answer is written down — worth noting while assembling it.

What the job actually involves

Rim brakes

Take the wheel out to get it out of the way, undo the pad’s mounting nut and note the order the spacers came off in. Park Tool give two rules worth committing to memory: if the holder has a closed end and an open end, the closed end always faces forward — otherwise braking pushes the insert straight out of the holder — and the caliper arm should sit close to vertical as the pad meets the rim.

Check for a directional arrow on the new pads before fitting, and make sure the pad strikes the braking surface squarely rather than fouling the tire or hanging below the rim.

Disc brakes

Wheel out, then release the retaining pin or bolt and slide the old pads out with the spring. On hydraulic calipers the pistons need pushing back into the caliper body before the thicker new pads will go in — a tire lever or a cone wrench does it if you do not own the purpose-built spreader.

Fit the new pads and spring the same way round the old ones came out, refit the pin, and — this is the step people forget — pump the lever several times before riding to move the pistons back to the working position. The first pull after a pad change goes straight to the bar, which is alarming if you are already rolling.

Squealing is usually not a wear problem

New pads that squeal are more often contaminated than worn. Park Tool describe the test plainly: look for a darkness on the rotor and pads that smears when rubbed with a finger. Squealing, reduced power and that smear together mean contamination.

The usual culprits are aerosol lubricant overspray and hydraulic leaks. Both matter because the source has to be found — fitting fresh pads to a leaking caliper or spraying chain lube near a rotor again just ruins the new set too.

On rim brakes, squeal is more often geometry than contamination, and it is an adjustment rather than a purchase.

The habit worth building

Look at the pads whenever you pump the tires. The wheel is already in your hands and the pads are right there, so it costs you nothing and it is the only way this ever gets checked.

Keeping a spare set in the toolbox is the other half of it. Pads are small, cheap and do not expire in any practical sense, and the alternative is discovering the problem on a Sunday with the shops shut.