Module 2 of 3 · 45 minutes
Brakes: the only part that must never fail
By the end of this module you will be able to
- Set up rim brake pads correctly, including height, alignment and toe in
- Adjust cable tension with the barrel adjuster and at the pinch bolt
- Recognise when pads, cables or a rim are worn out rather than misadjusted
- Describe the differences that matter with disc brakes
Work through it
1 interactive for this module, built on the WAJD Teach engine. Nothing moves until you ask it to, and every one has a written version if you would rather read it.
Amara My brake lever comes almost to the handlebar before anything happens. Do I need new pads?
Nadia Probably not, and this is the commonest wasted twenty pounds in cycling. A lever coming to the bar is usually cable slack. Look at the pads first: if they still have grooves in them, they are fine and the cable is the problem.
Amara So how do I take up the slack?
Nadia The barrel adjuster, which is the little knurled barrel where the cable enters the lever or the caliper. Turn it anticlockwise, so it unscrews outwards, and it pulls the cable tighter and brings the pads in. A quarter turn at a time, checking as you go.
Amara And if I run out of adjustment?
Nadia Then wind the barrel all the way back in, undo the pinch bolt at the caliper, pull a few millimetres of cable through with pliers, hold it, and do the bolt back up. Now you have the whole range of the barrel adjuster back for fine tuning later.
Amara Let us talk about the pads themselves. What am I setting?
Nadia Four things, and in this order. Height, alignment, toe in, tension.
Amara Height first.
Nadia The pad sits fully on the braking surface of the rim, square, with a small gap below the tyre. And this is the one that hurts people. A pad set even slightly too high will rub the tyre sidewall, and it will cut through it. Not might. Will.
Amara What about too low?
Nadia Worse in a different way. A pad that sits below the rim can dive underneath it under hard braking and jam the wheel. Square on the braking surface, every time.
Amara Toe in. I have heard mechanics say this and never understood it.
Nadia Set the front of the pad to touch the rim a fraction before the back. About the thickness of a coin. That is it. It stops the pad chattering against the rim, which is where brake squeal comes from. A folded piece of card held behind the back of the pad while you tighten it will set it for you.
Amara Now the thing I would never think to check.
Nadia The rim. Everybody checks pads and nobody checks rims. Every time you brake you are sanding the rim away, and most rims have a wear indicator, a groove or a dimple in the braking surface.
Amara And when it wears through?
Nadia The sidewall goes concave, and eventually it splits under tyre pressure and the tyre comes off the wheel. Run a fingernail across the braking surface. If it dips into a hollow, get it looked at before you ride it again.
Amara Anything I should never do?
Nadia Never let oil, chain lube or degreaser near a pad or a braking surface. And on hydraulic disc brakes, never pull the lever with the wheel out, because the pistons close up and you will be resetting them with a tyre lever and a lot of swearing. Put the plastic spacer in. That is what it is for.
The written material
Everything else is comfort
You can ride a bike with a worn chain, a buckled wheel, a saddle at the wrong height and gears that will not index. You cannot ride one that does not stop. Brakes are the one system where good enough is not a standard.
Most braking problems people live with are adjustment, not wear. A lever that comes most of the way to the bar usually means cable slack, not new pads. Learning to tell those apart saves money and, more importantly, stops people replacing the wrong thing and still not stopping.
Rim brakes: the four adjustments
Height. The pad must sit fully on the braking surface of the rim, square to it, with a small gap below the tyre. A pad set too high will eventually contact the tyre sidewall and cut through it. A pad set too low can dive under the rim under braking, which locks the wheel instantly.
Alignment. The whole face of the pad should contact the rim, not just an edge. Looking straight down at the pad, it should be parallel with the rim.
Toe in. Set the front of the pad to touch the rim very slightly before the back, by about the thickness of a coin. This prevents the squeal caused by the pad vibrating against the rim.
Cable tension. Adjust with the barrel adjuster for small changes and at the pinch bolt for large ones. Aim for the pads sitting one to two millimetres from the rim, with the lever firm well before it reaches the bar.
Knowing when it is wear, not adjustment
Pads: replace when the grooves are gone. The grooves exist to clear water and to show wear, and a pad worn past them stops far worse in the wet.
Cables: a cable with broken strands at the lever or a rusty, gritty inner will feel stiff and spongy no matter how you adjust it. Cables are cheap and are the most common cause of brakes that feel poor after a winter.
Rims: a worn rim is the one people miss. Most rims have a wear indicator, either a groove or a dimple in the braking surface. When the groove disappears or the sidewall looks concave, the rim is done. A worn rim can split under pressure and the tyre comes off. Run a fingernail across the braking surface; if it dips noticeably, get it checked.
Disc brakes: what is different
Discs are more powerful, work far better in the wet, and are less forgiving of contamination. Three rules matter most.
First, never squeeze the lever with the wheel out of a hydraulic disc brake. The pistons come together and will not go back without being reset. Put a spacer in whenever the wheel is out.
Second, contamination is close to fatal for pads. Do not touch the rotor or the pad faces with your fingers, and keep all lubricant well away. A contaminated pad usually cannot be recovered.
Third, new pads and rotors need bedding in. Ride at moderate speed and brake firmly to walking pace, twenty or thirty times, without coming to a complete stop. Skipping this leaves you with weak, noisy brakes and people conclude the brakes are faulty when they are simply not bedded.
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