I was going to post this in my thread about the brakes that won't stop squealing. But then I thought it should be its own thread.

A lot of us joke that squealing brake shoes save money and weight because you don't need a bell.
Right, it's all very funny, as long as we all know we're joking, but this thread is to point out the fallacy of that joke.

Brake squeal is typically pretty high-pitched, like well over an octave above A-440. For the sake of argument, I think it might be somewhere around 1000 Hz, which means a thousand cycles per second, which means the brake shoes are grabbing and releasing the rim a thousand times per second to make this sound. Each time they grab the rim, the brake shoes deflect forward with the rim until they release and spring back to where they started. Then they grip the rim again, and the cycle repeats.

The problem is that since they deflect when they grab, they are moving forward, rather than staying put, so there is much less braking power than there would be if they would stay put. And obviously when they release the rim there is no braking effect at all. If we assume they spend about half of the cycle grabbing the rim and the other half springing back, their actual time spent in contact with the rim is reduced to 50%. And since they deflect on contact with the rims, there is a further reduction. Bottom line, squealing reduces the effectiveness of your brakes by at least 50%, and possibly much more than that.

Aside from that, deflection means the brake arms are flexing, which will inevitably lead to metal fatigue and premature failure.

In conclusion: yes, squealing brakes are a bad thing. Squealing brake shoes are dangerous because they are ineffective for stopping your bike, and potentially prone to catastrophic failure. And they're annoying.

Comments?

My guess is that these grab-release cycles occur in all brakes, but due to arm lengths, pad composition and braking force fall usually out of the audible spectrum, either by having too high a pitch or the sound being so soft that it's not audible over environment noises unless you get really close. I think the movements of the calipers are well within the material tolerances and fatigue limit of the brakes, so no worries there. Also, the release cycles are a good thing - locking up your wheels all the time would be very dangerous. Plus, repeated cycles only increase friction and that's what you want, because braking in the end is the transformation of kinetic energy in heat, sound etc.

My verdict: not a bad thing. But an annoying thing.

In my opinion, absolutely! There is no excuse for squealing brakes. They can be fixed, every time, if you take the time to understand the system and implement the repair(s) required. I have built hundreds of bikes, and never released one with squealing brakes. And to that add this...

I like to ride my bike and I do not like to hear the bicycle while I am riding it. Loud freewheel clicking, noisy brakes, poorly engaging chains/sprocket teeth, and the like are awfully annoying. And the worst of all....

Those bloody patterned steel wheel rims, often found on lower end European bicycles like this seventies something Jeunet Mixte. What a nasty buzz!!!


Of course, that is my opinion.,

Like anti-lock brakes on a car? lol..

I berate anyone who rides with me with squealing brakes (or doesn't trim their derailleur for that matter). Either they'll fix them or de-friend me. It's worked out alright so far.

Isn't that sort of what anti lock brakes on automobiles do? Well, maybe not quite as fast....

AH!! Jeepr beat me to it.

I put some of those Kool Stop Salmon pads on my old Record brakes and I've done everything to make them stop squealing, except bend the calipers as some have recommended. The brakes are original to my beloved Holdsworth that I've had since 73 and they're not getting bent. The front squeals a lot with heavy pressure, but it stops just fine and doesn't bother me any more.

Could the problem be wiyth the rims and not the brakes? I'm asking because I have no idea and am curious.

Probably a combination of the two. The rims are Fir hardox box tubulars. I cut 3 grooves in the pads like on the Campy originals to no avail. I'm wondering if the squealing will abate once the pads wear more parallel to the braking surfaces. I also have other wheelsets to try.

It's pretty easy to shim out a brake shoe rather than toe it in. Just break off the pull tab from a soda can, put it between the brake shoe and the brake arm (in front of the bolt), tighten it up, and break off the rest. No bending required.

I just put a drop of oil on my pads... No more squealing. No more brakes either

That is a pretty slick method. have to keep that one in my hat for the future.

Rudi, you don't strike me as the kind of guy that would drink pop. Maybe you mean "cheap beer can tab"?

No one would be caught dead drinking pop back East - everyone drinks soda!

Pop? What? Are you from Ohi. . . oh, yes, you are from Ohio. Carry on.

Matt, you're absolutely right, I don't drink pop, but I do pick up trash from the side of the road sometimes, so I'm pretty familiar with pop containers.

And my mother is from western NY (Buffalo!) so I'm familiar with the term 'pop.' Where I grew up, in DC, we called it "Coke." As in "what kind of coke do you want? We have ginger ale, tab, pepsi, and 7up."

That's how it is in Kentucky too.

I shoulda said RC Cola. Or Moxie.

if they stop well and annoy atleast 20% of the group they are FABULOUS!!!

There was one time I was glad someones brakes were squealing.

Three of us were mountain biking in Jasper National Park. One of my friends went over the bars near the end of a 20 mile ride. When we got back on our bikes and went around a corner a bear was on the trail. I think it heard us coming thanks to the odd squeal of brake pads. As a result it wasn't startled and the three of us didn't end up a statistic on a chart somewhere.

These grab-release cycles are a fact of life. Any braking surface is going to do it -even on cars/motorcycles. Brake surfaces can't "slide" by each other but will necessarily cycle at a frequency determined by the co-efficient of friction of the braking surfaces, the amount of force squeezing them together as well as the resonant frequencies of the parts involved. The trick is to avoid having the frequency of this oscillation within the human range of hearing purely for aesthetic reasons.

Many times the effort to keep the vibration out of the human hearing range causes the designers to choose materials or designs that are less-effective at the primary job intended (braking) in order to meet the aesthetic audible (or inaudible as the case may be) demands of the brake.

Big truck brakes, or those used in high-performance racing applications often tend to make more spurious noise as the requirements for fully-effective brakes simplhy outweigh any cosmetic or aesthetic considerations.

But on a bicycle, where braking performance is typically abysmal anyhow, and the requirements are not that great in the first place, it's fairly easy to tune out audible brake noise without giving up anything in actual braking performance. Usually just fiddling with pivot fastener tension/slack and toe-in it can be easily tuned out of the audible range.

-My $.02

From: https://www.sheldonbrown.com/brandt/brake-squeal.html

"Subject: Brake Squeal
From: Jobst Brandt
Date: May 11, 2001 Most car, motorcycle, and bicycle brakes squeal at one time or another because they involve stick-slip friction whose frequency is supposed to be out of audible range. Squeal is not only annoying, it decreases brake efficiency, especially in the lower frequencies where the length of slip motion exceeds that of stick.

Brake noise requires elastic motion (vibration) at the sliding interface, with at least one element in rapid stop-start motion. Because bicycles use hand power and demand light weight, they use relatively flimsy mechanisms and demand pads with a high coefficient of friction. The brake material must be soft and pliable enough to achieve good contact on relatively rough rims. The brakes generally have a mechanical advantage between 4:1 and 6:1 from hand to rim, as described under "Brakes from Skid Pads to V-brakes." That's not much compared to motorcycles that have hydraulic disc brakes with practically no pad clearance. For a hand brake, free travel (pad clearance) and flexibility defines the limit of mechanical advantage.

Soft brake pads and lightweight (flexible) calipers promote squeal and chatter, chatter being the mechanically more detrimental version of stick-slip behavior. Brake chatter is caused by gummy residue on the rim together with excessively flexible (skimpy dimensioned) brake mechanism. Rims can be cleaned but flexible brakes can only be fixed by using better brakes. If the rim becomes gummy again after cleaning, then either the rims are being contaminated by something like riding through tar weed or the pads are no good. My solution for pad quality is Kool-Stop salmon red pads.

Squealing brakes, the more common problem, involves mainly brake pads that generate caterpillar like surface waves. The common advice is to bend the brake caliper to make the trailing edge of the pad (with respect to rim motion, the forward end of the front brake pad) contact first. This is not entirely without merit because toe-in is the natural state of a used, non squealing brake. Elasticity of the caliper, however small, allows the pad to follow the rim and rotate forward about the caliper arm, wearing the heel of the pad more than the toe, causing toe-in. Toe-in is preferred because a pad that makes full contact as it first touches the rim will rotate slightly from frictional drag, reducing contact... and drag, which allows it to snap back and repeat the action. This causes surface waves in the pad, especially when it is new and thick. For this reason, some pads are made with thin friction material to reduce elasticity.

If the pad contacts the rim, trailing end first, it develops full contact stably as pressure and frictional drag increase. However, the brake may squeal anyway. This can occur with new rims or one with wax or oil, or from other contaminants like riding across a moist lawn. New pads often have a glossy sticky skin that should be removed either by sand paper or use. Many types of rim contaminants that increase stiction (stick-slip) can be removed easily by abrasive scrubbing. This can be done by braking at moderate speed with a dusting of household cleanser on a moist rim, followed by a water bottle squirt rinse (also while braking). This process is more conveniently achieved by slowly riding through a long mud puddle while braking or by descending a mountain road in the rain where there is usually plenty of fine grit and where rain supplies the rinse.

Some rims have machined brake surfaces with fine grooves whose roughness reduces squeal tendencies so they don't have to be "broken in". Martano rims of old had somewhat larger grooves as part of the extrusion for this purpose.

Avoid bending brake calipers. This is "cold setting" in its worst form. Aluminum in such cross sections doesn't bend far without structural damage. Besides, this remedy could lead to more bending with each occurrence of squeal that is better abated by other means."

(My underlining. -Randy)

I've never had any issue with any brakes I've ever adjusted by "cold setting." This includes vintage steel and alloy brakes as well as more modern brakes that weren't modern enough to have a built in toe-adjusting mechanism.

The amount of bending required to change a degree or two is NOTHING compared to the amount of bending and torment these flimsy things see in their lifetime. If an alloy brake caliper can't take a tiny bit of twisting to adjust toe-in of the brake pads then they are just not going to survive the types of stresses the brake is going to see on a daily basis.

I call malarky on this fear of bending calipers to achieve proper alignment. Brakes are cheap anyhow. If they eventually fail then just replace them. It's not like we are running down the back straight at 140MPH and late-braking into the apex of turn 1 and scrubbing 80MPH in a second and a half.

I'd never trust any cheesy bicycle brake so much that if it were to fail I'd be in that much danger. Any brake can fail at any time and the typical bicycle brake is so cheesy that to ride in such a way as to necessitate 100% failure-proof braking components seems the ultimate in foolhardiness to me.

Unless I had some highly-prized collectible & valuable brake caliper I wouldn't hesitate to tweak it a degree or two. But that's just me and my $.02 -this isn't rocket science.

What about squealing brakes vibrating other stuff loose? I had some squealing brakes that would make my Presta valves rattle open... that was no fun.

I don't think squealing brakes stop any worse, but it can make modulability suffer.

Click and Clack, the Tappett Brothers, said (of car brakes):