Rest_assured

This might be the stupidest question ever asked-but why do freewheels and cassettes click or tick when coasting? I'm not asking how they click, but why? Why was this feature added somewhere along the line of bicycle evolution? When you actually think about,it is a bit strange. There must be a reason, but I can't think of one.
Just out of interest....
Cheers

contango 

Inside you've basically got a toothed wheel with pawls in it. When you pedal the pawls lock into the teeth of the wheel and make it turn; when you freewheel the shape of the teeth is such that they push the pawls out of the way, and when each tooth has passed a pawl it is pushed back into place by a spring.

It's not so much a feature that was specifically added, more an attribute of the mechanism that lets you pedal but also freewheel. If you've got a mechanical clock try taking the face off and seeing what happens when you wind it - it's much the same concept in the freehub when you're coasting.

Airburst

The clicking sound is a side-effect of the operation of the ratchet-and-pawl mechanism that allows the freewheel or freehub to transfer drive in one direction but not in the other, which is what allows you to coast.

Rest_assured

Ah, ok.
the only reason I even thought of it is because the Suntour cassette on my Fuji hardtail recently stopped clicking (or perhaps has become very quiet) for some reason. Now I think of it, it is an interesting distinction between some brands. My campy centaur group on my peugeot clicks quite loud and fast (almost like a buzzing when at high speed), and the suntour winner freewheel on my nishiki is a bit slower and quieter.
learn something new every day, thanks for the replies!

Kimmo 

Can you distinguish how and why in this context for me, please?

Cause from where I'm standing, there's no daylight between the two.

The how is why.

Rest_assured

Yeah I see that now, but I didn't realise that the noise was a product of the function. I guess I assumed that the clicking was some kind of added feature for some reason.

Kimmo 

Like a more sophisticated version of the playing card on a peg?



Try designing a freewheel that doesn't click and then get back to me.

Yellowbeard

Roller clutch. Bam!

Airburst

What was the Shimano freehub that was advertised as using a "silent clutch"? I believe it had a roller clutch mechanism.

HillRider

As a general rule, Shimano freehubs run quieter than Campy, Chris King, DT or other freehubs. Not dead silent but quieter. Shimano does make a completely silent freehub as mentioned above and it is directed at the bicycle police market to allow stealth riding.

Note to the OP: If your Sun Tour hub has suddenly gone quiet, that indicates the ratcheting mechanism is dirty or gummed up with old oil or grease and it is not a good sign. Sooner or later the pawls are likely to stick open it will "freewheel' in both directions. Time to solvent flush and re-oil it.

Yellowbeard

I have a Shimano Nexave FH-T400 hub that I scavenged from somewhere with a silent-clutch freehub. Been trying to find an excuse to use it ever since. Pretty heavy, though.

Retro Grouch 

It's been done. You can buy one from Shimano. Police bikes use them so they can sneak up on bad guys more quietly. It uses a roller clutch.

TallRider

I have the Nexave silent clutch hub on my commuter. As Yellowbeard said, it's heavy. But it works fine. I have 8k miles on it since building the wheel, and other than the poor drive-side sealing (had to replace a weird-dimensioned cone) it seems pretty bombproof.

I tend to think that form does matter somewhat, independent of function, on this issue. Obviously it's possible to make a silent clutch but they tend to be heavy. But as to why Campy and Chris King are much louder than Shimano, there is a matter of preference on this matter and not a question of function or durability. For some cyclists, it's the closest they'll ever get to a Harley, while feeling high-end and high-tech.

Retro Grouch 

government officials have always been concerned that bicyclists were using the public roads and having fun but not paying any taxes for the privilege. The "click" that you hear is a experimental program that signals a satellite to keep track of where and how far you ride. I know because my son-in-law is working to perfect the software. Expect a tax bill in the mail soon.

contango 

Best answer so far

FBinNY 

Rather than thousands of words, here's an explanation with some pictures that show why they tick.
The freewheel is basically a ratchet, which drives in one direction, and over runs (freewheels) in the other.

Booger1

Get a tricycle.....drive to the biggest hill around......mount tricycle.....STRAP FEET TO PEDALS.......ride down said hill.....and don't forget to stop at the red light at the bottom....Enjoy!....

Kimmo 

I know it's been done, but I've yet to examine one, and it's tough to imagine how it works.

I pulled the brake shoes out of a coaster hub once, but the take-up was immense.

FBinNY 

Actually there is a semantic difference. How described the mechanical cause. Why, goes to intent. In the case of freewheels, might be about why, among of overrunning clutch designs, bikes are built with ratchets vs other designs that are silent.

JohnDThompson 

The frequency of the clicking is a function of the number of pawls and the number of teeth in the ratchet mechanism. More pawls and/or more teeth will result in a higher frequency of clicks for any given speed.

The volume of the clicks can depend on the presence or absence of lubricant and its viscosity in the mechanism, and also on frame construction. Frames with large diameter tubes tend to resonate more loudly than frames with smaller tubes.

JohnDThompson 

FWIW, the old Sturmey-Archer SW series hubs used springless pawls that were virtually silent. And there are some pawl-less clutch mechanisms that are completely silent.

SJX426 

IRD's are very quiet. Spring force can also influence the sound level.

Clawed

My Shimano Nexus IGH is dead silent. People have complained to me about it.

Airburst

In general if you pack enough grease into a freewheel mechanism to stop it making any noise, it'll gum up after a while as the grease goes hard with age, so I'd be careful doing that, I just use oil on freewheel mechanisms. However, automotive bearing grease is a perfectly reasonable grease for all the other bearings on a bike.

sreten

Hi,

You can make a silent (no clicking) freewheel with a spring clutch at the cost
of possibly some slight slipping in forward drive and some drag freewheeling.

Basic arrangement is a driven square section multiturn coil wrapped
around the output shaft with some spacing between the coils.

Freewheeling drag opens the coils allowing it to slip whilst drive drag tightens
the coils giving you drive. Never be as efficient as the standard method though.

I'm trying to think of the application I've seen this work well, but I cannot recall.

rgds, sreten.