Maintenance - replacing brake pads

Timothy John Timothy John

Winter conditions are notoriously hard on bicycles.

Brake pads and wheel rims are among the components that bear the brunt of the additional water, grit, and debris thrown from the road surface at this time of year.

Pads, nothing more sophisticated than small blocks rubber, are placed under immense strain by the greater pressure required to generate friction on a wet or dirty rim.

Brake pads - worn pads close up
The wear sustained by this pad is obvious from its thinness

The coating collected by the pads from the water and from road grime places additional wear on the rim, an integral part of the braking system for caliper brakes.

In extreme, but not uncommon, cases, the rim will crack; the result of being reduced by wear from the pads to a thickness no longer able to support the pressure of the tyre.

“Checking your pads and rim surface is equally important – especially in the winter,” says Jon Hayes of independent bike shop, Ride.

Our demonstration involves cartridge pads: a design that allows replaceable rubber inserts to slide into the brake shoe. The metal shoe is more resistant to flex than a rubber block and so offers better stopping power.

Step one – remove the wheel

While it’s possible to replace cartridge brake pads with the wheel in situ, it’s easier to do so if the wheel is removed, a process that takes seconds.

Brake pads - removing rear wheel
It’s easier to replace brake pads when the wheel has been removed

If you’re replacing pads at the rear, shift to the outer chainring and the smallest cog on the cassette. In either case, front or rear, release the lever on the caliper before removing the wheel.

Step two – inspect the wheel rim

Removing the wheel presents an ideal opportunity to check the braking surface of the rim. Some come with wear indicators, typically a groove around the circumference, below the brake track, or a series of dots at regular intervals. When the groove or dots have disappeared, it’s time to replace the rim.

Brake pads - worn rim sticker
The poor condition of this graphic is evidence of wear suffered by the rim

A further indication of rim wear can be found in worn graphics. “As the pads become thinner, their orientation to the rim changes, and they move down towards the sticker,” says Jon. Unless you have experience as a wheel builder, replacing the rim is likely to be a job for a professional.

Step three – unscrew the pad from the shoe and remove

The Shimano units illustrated here use a 2mm grub screw to hold the pad in the brake shoe. If the replacement pads come with a new grub screw, use it: the heads are easily rounded. Some of Campagnolo’s upper end pads use a spring clip.

Brake pads - screwdriver
Pads can be persuaded to leave the shoe with use of a screwdriver

Remove the pad. “Sometimes they need a bit of gentle persuasion,” says Jon. A flat-bladed screwdriver will aid your cause if this is the case.

Step four – inspect the pads

Worn pads are likely to be thin, perhaps with a groove at the centre or elsewhere, depending on their prior orientation. Those pictured have developed a ‘lip’ at the top. It’s time for a new set.

Brake pads - pick
Silver particles on the pad are likely to be pieces of aluminium from the rim. Remove with a pick if the shoe has sufficiently good to be used again

Check the pads for debris; typically small pieces of aluminium from the rim. If your existing set still has some life left, you’ll want to remove debris to prevent unnecessary wear to the rim. “It’s part of a good winter maintenance routine,” says Jon. “Ideally, it will be part of cleaning the bike.”

Step five – install new pads

The orientation of the pad is critical. Fitting the shoe with the open end facing forwards is a recipe for disaster, says Jon: the rotation of the wheel will pull the pad from the shoe.

Pads are also oriented for the left and right side of the caliper and typically marked ‘L’ and ‘R’. If the new set comes with a replacement grub screw, fit this too: they’re easily rounded with use.

Brake pad - grub screw
Grub screws can wear and easily become rounded. If your replacement pads are supplied with new grub screws, use them

If you’ve replaced worn pads, it’s likely the cable tension will be too great for their new, unworn replacements, placing them against the rim. Reduce the cable tension by turning the caliper’s barrel adjuster clockwise.

Make a final check of pad alignment and check the brake function. You’re ready to go.

Types of pad

Certain wheel rims demand specific pads: Mavic rims with the proprietary Exalith coating, for example, require use of the French manufacturer’s own pad. Similarly, carbon rims, an unlikely choice for winter, require specific pads.

Standard pads can be used with aluminium rims. Pads vary in quality, however. Jon recommends Shimano and SwissStop. Shimano and SRAM pads are interchangeable, he adds, but warns that Campagnolo’s pads are specific to the brake caliper.

Final thoughts

Riding regularly in a group will increase pad wear, says Jon. The additional braking required to maintain a distance to the rider in front, and the concertina effect that causes heavier braking for riders in the middle of a pack responding suddenly to the deceleration of the riders at the front, are two causes.

Brake pads - new
New pads and regularly inspected rims – a safe combination

Another thought provoking issue: a worn rim will one day collapse. The consequences can be catastrophic. As the rim becomes thinner and thinner, it will start to bow outwards beneath the pressure of the tyre. When the rim is no longer strong enough to bear the pressure of the tyre, it will crack, and large sections will peel off.

“It’s extreme, but it happens,” says Jon. “It happened to a guy I was riding with recently – luckily on a flat piece of road.”

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