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Safe Braking and Why Do Brakes Squeal?

In Spring Maintenance Series post #2, we look at how to make sure your brakes will stop you safely, the science behind why some brakes squeal, and how to fix the annoying problem.




The Underrated Brake System


Because, who wants to stop? When riding your bike, you probably think mostly about how it feels when you are pedaling, wind in your hair, scenery going blissfully past. The feeling of freedom. However, making sure you can stop when needed is just as important to keep the good times rolling! Your brake system has multiple components, all of which must be in good working order to bring you to a stop when danger arises. Those components are: the levers, the housing, the cables, the brakes, the brake pads, and the rim (or disc). Let's look at the components one by one to see how to make sure they are functioning properly.


The Levers


Squeeze The Levers --
It all starts at the levers. You can get a really good feel for how your brakes are working by just squeezing the levers. If the lever goes all the way to the grip, you know you have a problem. If your lever is squeezing about half-way to the grip and has a solid end feel, you know you are in the ball park of a good functioning brake.


Push Down On The Levers --
They should be tight on the bar and not move. If your lever is loose, re-align them to the angle you like best, and then tighten the pinch bolt to the proper torque specs. If you do not have a torque wrench, tighten it as much as you can without stripping the bolt.


The Housing And Cables


Visually Inspect The Housing --
As housing ages, it can become brittle, break, and explode. If you have soft feeling brakes, or continually lose cable tension, there is a good chance that your housing is compromised. If needed, replace your housing and cables.
Visually Inspect And Feel The Cables --
When cables run over a rough surface, they can become frayed and eventually break. Look over any exposed part of cable, especially near where they enter and exit the housing, where they leave the levers, and where they are pinched at the brake. If you notice that the cables are frayed, it is best to replace them right away. Sometimes, the cable can be frayed inside of the housing and you can't see it. Pull on the levers slowly. If you feel that the cable is pulling roughly or getting caught-up inside of the housing and not returning properly, pull the cables and either repair or replace them.


The Brake


The brakes have bolts that hold them onto the frame and fork. Inspect the bolts and make sure that the brakes are tightened properly. If your brake is loose, there is a good chance that you will have poor braking power and increased squealing. If your brake is pulling uneven, the spring tension on one side is probably stronger than the other. There are adjustment screws on the side of the brake to adjust the springs. Either tighten the weaker spring, or loosen the stronger spring so that they pull and rebound evenly. This will ensure that your pads are contacting your rim at the same time, optimizing your braking power.


The Brake Pads


Overly Worn Pads --
Your brake pads have wear indicator lines on them. They are grooves cut into the rubber to show you when it is time to replace your pads. If you do not see any grooves in the braking surface of your pad, it is likely that you will need to replace them. Past the wear indicator line, there is a metal plate. If that plate is exposed, it will wear through your rim quickly. When that happens, it will not only be a costly repair, but could be a major safety concern.
Old Pads --
Even if your pads are not past their wear line, there is a chance they are not working as well as they could be. When not used, the rubber can harden and reduce the friction between the pads and the rim (or disc). If that is the case, you can either use some fine grit sandpaper to resurface the pad, or just replace them with new pads.
Dirty Pads --
Either from road debris and rain water, or from lubricants, or dust, your pads can become contaminated. They again will lose the proper friction to give you good braking power. You can clean your pads with rubbing alcohol or degreaser and a clean rag. If needed, take out any embedded dirt or foreign objects.


The Rims Or Discs


The rim itself may have a film, lubricant, dirt, or dust on it. This barrier between your rim and pads will decrease your braking power and could be the cause of squealing. Clean the braking surface of your rims (or disc) with rubbing alcohol or degreaser and a clean rag. If needed, you can also rough up the surface with fine grit sandpaper to remove any embedded dirt and restore a clean and smooth surface. When checking out your rims, also look to make sure that they are not overly worn or have been dented. A compromised rim can impact your braking and can have serious safety implications.




All braking requires what is referred to as the stick-slip phenomenon. When properly adjusted, this rapid oscillation of grab and let-go slows the wheel at a rapid pace without binding. When the motion is at the proper frequency, the vibration it causes is outside of the audible range. When one or more parts of the system are not working properly, the frequency of the vibration will either be too low (causing a groan - uncommon), or too high (causing a squeal). Let's look at the different components of the brake and how to fix a squealing problem.


The Brake Pads


The first thing we look at as mechanics when attempting to cure a squealing brake, is the brake pads themselves. When the pad hits the rim, because of the flex in the brake arm and the pad, the pad will slightly rotate forward. This is natural for all brakes. Higher quality brakes will have less flex in the brake itself, and will have less flex and rotation, but the force the rim is putting on the pad will always cause a minor forward rotation.
If the pad initially hits the rim flat, when the pad rotates forward, the trailing edge (in relation to the direction of the rim's spin), or the front of the pad, will lose contact with the rim. When the slip portion of the stick-slip happens, the front edge will again contact the rim. This vibration, happening over and over, causes a high frequency tone that resonates through the brake and the frame, producing a high pitched squeal.
To fix this issue, we generally attempt to "toe in" the brake pad so that the front of the pad hits the rim first just slightly before the rear of the pad. All of the pads on our bikes, and most pads these days, have a curved washer on the pad that allows you to adjust the angle. You'll generally want 2-5mm of difference from when the front pad contacts the rim to the rear. You could use the thickness of a business card as a reference.
If the pads are angled properly, and you still are getting squealing, clean and resurface the pads with a fine grit sandpaper to make sure the rubber is getting proper grab. Do the same with the rim to make sure there isn't a build-up of dirt or film.


Not The Brake Pads


If cleaning and resurfacing the pads and rim do not do the trick, check the bolts that hold the brake arms to the bike. If the brake arms are loose, it will allow for excessive rocking of the pad, again causing the high-frequency vibration.


Can't Figure It Out


If none of that works, you may just need to ride and brake for a little while to let the pads wear-in. Your pads should develop a natural "toe" because as the rim pulls the pad forward during braking, the rear of the pad should wear more quickly than the front, giving you a natural front of pad initial contact. If it doesn't go away within a ride or two or decent braking, you could try replacing the pads, or taking it to a mechanic to see if they can spot the issue.




The squealing sound brakes sometimes make does not necessarily mean the bike is unsafe to ride. You may still be getting decent stopping power with a squealing brake. Make sure to test your braking in a safe area before going out for a ride. You might be the annoying squealing person out there, but by all means, make sure you can stop quickly when a gaggle of geese decide to cross the road in front of you, and hey, at least they will hear you coming :).



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