Replace rim brake blocks

Start by identifying your brake. A road caliper brake has a small quick-release lever on its side: flip it up. On a V-brake, squeeze the two arms together and lift the noodle, the curved metal tube, out of its holder. On a cantilever, unhook the straddle cable from one arm.

The arms spread apart and give you room to work. Clean the rim's braking track with a rag soaked in isopropyl alcohol: new blocks on a greasy rim brake poorly and glaze over within the first few kilometres.

Compare your blocks with new ones: when the grooves have almost gone, it is time. On a road brake, the blocks are often rubber inserts slid into a metal holder and held by a small screw: remove the screw with the Allen keys (or else Multi-tool), then slide the old insert out towards the back, helping it with pliers if it sticks.

On a V-brake or cantilever, the whole block comes off: undo the nut holding it to the arm and pull it out, keeping the domed and cupped washers in order. They let you angle the block and go back in exactly the same order.

On a cartridge holder, slide the new insert in from the open end, the right way round: inserts are often marked left and right, with an arrow showing the direction the wheel turns. The closed end of the holder faces the front of the bike. Refit the small retaining screw, which stops the insert from sliding.

For a complete block, pass its post through the arm with the washers in the same order as before, and barely tighten the nut: the block must still move by hand. Do not touch the braking surface of the new blocks with greasy fingers.

Close the brake for now, then gently squeeze the lever. Set each block so it meets the braking track squarely, along its whole length, about 1 mm below the top edge of the rim. Never on the tyre, never below the sidewall.

Give it a slight toe-in: the front of the block should touch the rim a little before the back, with a gap of about 1 mm at the heel. A thin card slipped behind the rear of the block while you tighten helps hold it there. Keep the block in place and tighten the nut firmly, to the torque given by the brake maker, stopping the block from turning.

Close the quick-release lever or put the noodle back: this is the most common thing to forget, and the most dangerous. New blocks are thicker than old ones; if the brake rubs the rim all the time, screw the cable's barrel adjuster in a turn or two, or unscrew it if the lever feels too soft.

Spin the wheel: it should turn freely, with no rubbing. Squeeze the lever hard: it should be firm well before the handlebar, and both blocks should reach the rim at the same time. If one side touches first, re-centre the brake. Finally, test the brakes at low speed before riding off.