How to Tell When Brake Pads Are Worn

The brake feels weaker, or it squeals, or the lever travels further than it used to. Worn pads are the first thing to check, and the check is quick.

Start with the symptoms

Two symptoms are worth noting: a squeal, and needing more effort at the lever to slow down. Both can come from oil or dirt on the pads, not only wear. Park Tool links contaminated pads to a squeal and to extra effort at the lever.¹ It lists three reasons to replace pads. They're worn out, they're contaminated, or you want a different pad material.¹

Look at the pads

Your brake manual shows how to see or remove the pads, and the steps differ between calipers. Before you handle them, a warning from SRAM: keep your fingers off the pad face and the rotor.² Skin oil is enough to cause trouble.

Look at the friction material, the layer bonded to the metal backing plate.³ That layer is what wears away, so it's the layer to measure.

How thin is too thin?

Park Tool gives a general figure. Generally, the pad material should measure at least 1mm thick.¹ For a rough gauge, stack 3 business cards. That makes about 1mm.¹

It's a general guide, not your brake's rule. Park Tool also says to ask the pad maker for exact wear specifications, and to use a caliper for accurate measurements.¹ Find your own maker's limit, and measure the way that maker's manual describes.

Pads that look fine but don't work well

Check for contamination. Park Tool names brake fluid, oil and grease as the usual culprits, and says they're hard to spot. One sign is a darkness on the rotor and pads that smears under a finger.¹ Common sources it lists are overspray from aerosol lubricants and a leak in the hydraulic system.¹

Oil on pads is a sign to find the source, not only to swap the pads.

After the pads change

New pads need the right shape for the caliper. SRAM says each of its calipers needs a specific pad shape for proper fitment.² Other makers have their own parts, so match pads to your brake's model.

Wikipedia notes that several adjustments are often required during the life of the pads.⁴ On mechanical brakes in particular, Park Tool says the barrel adjuster isn't for taking up pad wear.³ See mechanical and hydraulic brakes for that detail.

Hydraulic brakes need care too. New pads are thicker than worn ones, so Park Tool says the pistons must be fully pressed back to make room.¹ Squeezing the lever with the wheel out pushes them back out. Follow your manual for the order of steps, and ask a shop if you're unsure.

Fresh pads and rotors also need bedding in before they work at their best.