Tech Talk
Squealing Brakes: Nothing is more annoying than grabbing your brake and hearing a noise that could wake the dead. On the surface, this squealing seems like it should be easily remedied. However, the harmonics involved can actually be quite complicated to resolve.
On rim brakes, the rim surface of the wheel, the brake pads, and the brake’s pivot points all wear over time. Play in the pivot points on the brake itself can cause a vibration that turns into a squeal. Likewise worn, contaminated, or hard brake pads can cause a squeal, as can a contaminated or worn rim. Frustratingly, replacing old worn pads with new pads on a brake that was not squealing can cause that brake to start squealing. Sometimes the solution is a different style or brand of brake pad. Sometimes the solution is a new brake.
With disc brakes, the rotor, the brake itself, and the pads, can all contribute to brake squeal. The most common source of disc brake squeal is contaminated pads and rotors. If oil or grease get onto the rotor, and then into the brake pads, the brake will still stop well, but it will most assuredly squeal. Sometimes, cleaning the rotor and sanding the pads will do the trick. Usually, however, new pads are in order, along with new rotors. If the old rotors are used, there is always the possibility of contaminating the new pads. Rotors develop a coating on the surface that usually can only be removed with heat. That’s how an old rotor can contaminate a new pad: the pad and rotor heat up under braking and the coating on the disc melts into the pads. Pads that have been contaminated with grease or oil, can sometimes work quietly again by burning the contaminants out of the pads with a propane torch. This is a smelly and time consuming process. If you are a DIYer, and have a torch, have at it. If, however, you are paying a mechanic to do the work, it is cheaper to get new pads. Most shops, including mine, will not guarantee their work unless both the pads and rotors are replaced.
Frame clicks, creaks, and knocks – a deeper dive: Higher technology frames and parts, most notably the carbon versions, must be correctly lubed, installed and tightened, or noises may well erupt.
Frustratingly, if your bike is making a noise, it almost always sounds like it is coming from the crankset. Something as far away as a spoke in the front wheel - or the derailleur hanger in the back - not being tight, can result in a click or knock that sounds all the world like it is coming from the crankset, or what we call the “bottom bracket”. The reason that we hear the noise coming from there is both a function of acoustics, and of our perceptions.
The harmonics of frames is a result of several tubes coming together at the bottom of the frame. That portion of the frame can amplify a noise from somewhere else on the frame such that it sounds like the noise is originating from down in the area of the crankset. Carbon fiber frames are constructed with strands of carbon which are put under tension. That tension structure carries noise very effectively down to the bottom bracket area and amplifies the noise. If you want a good example of how a tension structure amplifies and carries sound, simply pluck a spoke on one of your wheels. You should hear the spoke, and wheel, “sing” (if you don’t, your wheel needs to be tensioned!)
The other part of this process that tricks us is that most clicks and knocks occur under load. Load is maximized when we are pushing down on the pedals. Our brain associates the noise with our pushing on the pedals, and tells us the noise is coming from the pedal/crank area. In reality, virtually every part of the bicycle is placed under load when we push on the pedals. A loose stem bolt, for example, can cause a creak that manifests only when we are pushing on the pedals.
Hear is a list, in approximate order, of the sources of knocks, creaks, clicks and “bottom bracket” noise:
Many of these things can be checked fairly easily and quickly. Some of them, however, can take quite a bit of time to work through. It is essential, especially on carbon frames and parts, that bolts are not tightened beyond the manufacturer's specified torque values. These values represent the upper limit of how much a bolt or nut should be tightened. Exceeding that value risks damaging the parts or the frame.
On rim brakes, the rim surface of the wheel, the brake pads, and the brake’s pivot points all wear over time. Play in the pivot points on the brake itself can cause a vibration that turns into a squeal. Likewise worn, contaminated, or hard brake pads can cause a squeal, as can a contaminated or worn rim. Frustratingly, replacing old worn pads with new pads on a brake that was not squealing can cause that brake to start squealing. Sometimes the solution is a different style or brand of brake pad. Sometimes the solution is a new brake.
With disc brakes, the rotor, the brake itself, and the pads, can all contribute to brake squeal. The most common source of disc brake squeal is contaminated pads and rotors. If oil or grease get onto the rotor, and then into the brake pads, the brake will still stop well, but it will most assuredly squeal. Sometimes, cleaning the rotor and sanding the pads will do the trick. Usually, however, new pads are in order, along with new rotors. If the old rotors are used, there is always the possibility of contaminating the new pads. Rotors develop a coating on the surface that usually can only be removed with heat. That’s how an old rotor can contaminate a new pad: the pad and rotor heat up under braking and the coating on the disc melts into the pads. Pads that have been contaminated with grease or oil, can sometimes work quietly again by burning the contaminants out of the pads with a propane torch. This is a smelly and time consuming process. If you are a DIYer, and have a torch, have at it. If, however, you are paying a mechanic to do the work, it is cheaper to get new pads. Most shops, including mine, will not guarantee their work unless both the pads and rotors are replaced.
Frame clicks, creaks, and knocks – a deeper dive: Higher technology frames and parts, most notably the carbon versions, must be correctly lubed, installed and tightened, or noises may well erupt.
Frustratingly, if your bike is making a noise, it almost always sounds like it is coming from the crankset. Something as far away as a spoke in the front wheel - or the derailleur hanger in the back - not being tight, can result in a click or knock that sounds all the world like it is coming from the crankset, or what we call the “bottom bracket”. The reason that we hear the noise coming from there is both a function of acoustics, and of our perceptions.
The harmonics of frames is a result of several tubes coming together at the bottom of the frame. That portion of the frame can amplify a noise from somewhere else on the frame such that it sounds like the noise is originating from down in the area of the crankset. Carbon fiber frames are constructed with strands of carbon which are put under tension. That tension structure carries noise very effectively down to the bottom bracket area and amplifies the noise. If you want a good example of how a tension structure amplifies and carries sound, simply pluck a spoke on one of your wheels. You should hear the spoke, and wheel, “sing” (if you don’t, your wheel needs to be tensioned!)
The other part of this process that tricks us is that most clicks and knocks occur under load. Load is maximized when we are pushing down on the pedals. Our brain associates the noise with our pushing on the pedals, and tells us the noise is coming from the pedal/crank area. In reality, virtually every part of the bicycle is placed under load when we push on the pedals. A loose stem bolt, for example, can cause a creak that manifests only when we are pushing on the pedals.
Hear is a list, in approximate order, of the sources of knocks, creaks, clicks and “bottom bracket” noise:
- Loose crank arm
- Loose wheel skewer or thru-axle
- Loose seat clamp
- Loose seat post clamp or un-lubricated seat post
- Loose stem bolt(s) – bar or steer tube
- Loose or dry headset
- Loose or dry bottom bracket
- Loose pedals, pedal bearings or noisy shoe cleat
- Loose derailleur hanger bolt
- Loose chainring bolt(s)
- Loose seat rails
- Cracked frame
- Loose spoke(s)
Many of these things can be checked fairly easily and quickly. Some of them, however, can take quite a bit of time to work through. It is essential, especially on carbon frames and parts, that bolts are not tightened beyond the manufacturer's specified torque values. These values represent the upper limit of how much a bolt or nut should be tightened. Exceeding that value risks damaging the parts or the frame.