Adjusting brakes

This article describes how to adjust common bicycle brake systems.

The brakes on bicycles are simple to adjust. They are an essential piece of safety equipment, so learning to adjust them is a worthwhile skill. Remember: after adjusting brakes, always try them in a safe environment before riding.

Rim brakes

Most bicycle brakes use a lever on the handlebars to pull a cable: that cable draws together a pair of brake arms, pressing the brake blocks against the rim of the wheel. Friction between the blocks and the rim is what slows the bike down.

First, check that you have good brake blocks and rims. Rims should be free of corrosion and dirt, and the brake blocks should be appropriate for the rim. Replace worn blocks in pairs.

• To clean steel rims of rust, use wire wool.
• Avoid getting harsh cleaning products on the tyres. Degreasers may corrode rubber.
• Leather-faced blocks are best for steel rims.
• Do not get oil, grease or wax on the rims or blocks.
• Excess dirt on rims and blocks will make them wear out faster.

The blocks should be aligned with the rim and slightly toed-in (to prevent squeal). To adjust them:

• Use a suitable spanner or allen key to slacken the block.
• Swing the brake arm in so that the block is pressed against the rim; fiddle the block so that it sits flat and square and tighten.
• The block needs to be toed-in - the leading edge should be about 1mm closer to the rim than the trailing edge. Use a piece of thin cardboard at the back of the block as a spacer when adjusting.

When both blocks are aligned correctly, slacken the brake cable clamp bolt and, using pliers, pull the cable through and hold it tight. Hold the brake blocks close to the rim and tighten the cable clamp bolt. This may take a couple of tries to get the blocks close to, but not touching, the rim. Fine adjustment may be made with a screw-thread adjuster barrel where fitted.

Note: A regular, periodic rubbing when the wheel is spun indicates that the wheel is out of true and needs to be trued.

The brake should be centered so that both blocks apply equal pressure to the rim. The method varies:

• For side-pull and centre-pull brakes, slacken the central retaining bolt and correct the position of the whole brake assembly.
• For cantilever and V-brake systems, there is a spring-tension adjusting screw on one or both of the arms. Adjust these to bring both arms into balance.

Changing a brake cable

Brake cables are braided wires with a metal lump at one end. This lump is a specific shape and is called the nipple. Usually, drop-handlebar ("racing") brake levers have a pear nipple and straight handlebar levers have a barrel nipple. Universal cables are available which have one at each end; you cut off the end you don't need. Brake cables run through a protective shroud called an outer.

To remove an old cable, slacken the cable clamp bolt on the brake. Pull the cable through the outer until it is all out at the lever, then remove the nipple from the lever and discard the cable. Steel cables can be recycled.

To install the new cable, put a little grease on the nipple and locate it in the lever. Then feed the other end of the cable through the cable outer, adding a little grease, until it emerges near the brake. Feed the end through the clamp bolt and adjust the brake as described above.

A new brake cable will stretch in use. You will need to take up slack after the first hundred miles or so, by adjusting the cable in the usual way.

Disc, hub and coaster brake systems

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