MTB Brake Pad Wear Limits
Safety, Performance, Predictability. All are reasons to check your brake pads regularly and change as appropriate. Let’s look at some basics about MTB Brake Pad Wear Limits.
First – when is a pad worn?
Magura, SRAM & Shimano Brake Pad Wear Limits
Brake pads are considered worn well before the pad material is completely gone. The image above (and text below) are published manufacturer sizes. (reference links below).
Magura brakes are to be replaced as soon as the backing plate and pad material measure less than 2.5mm in any section.
SRAM brakes are to be replaced when the backing plate and pad material measures less than 3mm in any section.
Shimano brakes are to be replaced when the pad material is less than 0.5mm.
Something to consider: running pads to full “worn” dimensions may compromise braking performance. I personally change brake pads at 66 to 75% of the full wear limit. As the pads wear past this level I tend to notice loss of power and heat capacity. Sidenote: I don’t have a brake sponsor, I buy brake pads too – but the extra few $’s a year for improved performance are worth it to me.
How about your rotors? Rotors wear too…
Magura, SRAM & Shimano Rotor Wear Limits
Magura rotors are to be replaced is any section of wearable area is less than 1.8mm.
SRAM rotors are considered worn if any wearable area is less than 1.5mm.
Shimano rotors are considered worn if less than 1.5mm OR if ANY aluminum surface appears.
Worn rotors as well as brake pads are dangerous. This goes without saying. When rotors wear they lose material rigidity as well as heat capacity.
If you replaced your brake pads but still find your bike down on power or feeling “spongy” after a proper bed in period you may have a rotor issue.
Other things to consider:
Potential MTB Rotor or Pad Wear Issues
Whether you’re a home mechanic or educating yourself before you come in for service here are some issues to look for as your brake system wears.
The far left rotor image shows a sloped wear pattern while the right rotor shows a concave wear. When rotors wear out of square it compromises contact surface area. This can reduce the brake’s efficiency and heat capacity – the two biggest factors in your brakes performance.
When brake pads wear out of square you need to review the rotor shaping as well as piston function. A semi-cocked piston may drive one edge of the brake pad into the rotor. Premature pad wear or etching can occur if the rotor has worn out of square or has anomalies.
Ever install new pads or rotors and have less power? Well, if you install new pads on old rotors you might actually be losing contact patch. Conversely if you mount new rotors with old pads you may have the same issues.
When your pads and rotors don’t have proper interface it is very hard on both pads and rotors due to heat input.
Bed In New Pads & Rotors
Remember when you replace your brake components you need to bed them in for maximum performance. Ride the bike in a safe location and apply the brakes several times to bring the new pads and rotors up to power. This is important! It’s really lame to drop into your first descent and realize you have about half brake power! (been there, done that.)
Odds & Ends
As your pads wear occasional bubble bleeds help maintain consistent lever feel. More info on MTB Bubble Bleeds.
Brake rotors may need to be resurfaced from serious heat input. More info on Resurfacing MTB Rotors
Disclaimer: If you have ANY doubts on your mechanical capabilities find a professional resource.
Links for Reference:
Magura Brake Manual – Page 22 of 28
SRAM Shifter & Brake Manual – Page 26 of 31
Shimano Brake Manual – Page 5 of 36