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I have only just noticed that my bike dosen't seem to make a lot of noise when free wheeling, in fact it's pretty much silent. Is this down to the fact that I have been putting off a major clean?, is my bike damaged? or is my bike equipped with a silent freewheel that I didn't know existed?

I am currently riding a Scott Aspect 30 - spec

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All of mine (various brands) have been relatively silent -- you can hear a click, but it's not loud. Others, I know, you can hear 20 feet away. –  Daniel R Hicks Feb 14 '12 at 13:35
    
Indeed, I had noticed the BMXers cruising past with majorly loud freewheels, just wondered why mine was so quiet. some of these answers are great. –  Wezly Feb 14 '12 at 20:04

4 Answers 4

up vote 6 down vote accepted

Your hub has a normal freewheel, like described by Matt Adams (ratchet with pawls).

There are some models which have spring-loaded cilinders mounted around "tilted" teeth: when you spin it to one side, the cilinders slip. When you spin it to the other side, the cilinders are caught between opposite surfaces, and torque is transmitted by friction (there is no positive engagement between parts).

Lots of backpedal-brake rear-hubs have this system.

Shimano had a Deore LX named "Silent Clutch" with this mechanism, but it was heavy.

enter image description here

Also, I know at least one model (American Classic) which instead of the spring to load the pawls, have a rotary disc to engage and disengage the pawl, and a tiny hair-sized spring which act as the freewheel for this plate. It is a very silent and low-friction system:

enter image description here

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Great pics of this in action! –  Matt Adams Feb 14 '12 at 21:27
    
I'm not recalling any pawls in either the Bendix or New Departure "coaster brake" hubs I took apart as a kid -- I think they both utilized a form of rotary clutch. –  Daniel R Hicks Feb 15 '12 at 1:31

Short answer. Hub integrity can not really be judged by noise alone, but by feel. If you feel it slipping under load the hub could be damaged beyond repair. The quiet smooth feel, but working normally is just a good, sealed hub that the manufacturer built in a way that has smaller or less splines.

The full monty. A free wheel hub consists of a few key elements. The splined hub body, springs and pawls. The spline is a series of ramped teeth. Slipping one direction, gripping the other. This allows the coasting. Fancy hubs may have more splines than cheaper ones.

The pawls are little teeth that grip the spline, and are spring loaded to keep them engaged when the cassette body is spinning faster than the hub.

So as a hub wears, its usually the splines or the pawls loosing their crisp shape, or the springs in the pawls no longer being strong enough to keep the pawl engaged.

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From my experience, silent hubs are those that have, inside, lots of grease (which dampens the clicking action of the pawls) or lots of dirt/rust (which creates friction and also block free motion of the pawls). If you don't ride in the weather/mud, and your hub works fine, there is no need to worry. –  heltonbiker Feb 14 '12 at 15:08
    
My hubs have been pretty much silent from the factory, and the current one is a reasonably good quality Shimano. I suspect that internal design has a lot to do with the amount of noise produced. –  Daniel R Hicks Feb 16 '12 at 1:29
    
But a chris king, and hope hub will make all kinds of noise because they have 2x the engagement points, and they are well known for being amazing. I think its somewhat a matter of design intent. –  Matt Adams Feb 17 '12 at 0:03

It very much depends on the freewheel mechanism in the hub, some make a nice "clickerty" noise, others are more silent.

The hub will be sealed and this should prevent dirt etc. getting into the mechanism. If anything it is likely to get noisier with penetration by dirt & grit rather than quieter.

Looking at the bike spec, my experience of Shimano hubs is they are quiet compared to other brands.

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We had the Shimano "clutch hubs" on some of our police patrol bikes. Seem to work well, my bike is about 15 years old and it's been trouble free.

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Police patrols seems like quite the right job for a silent freewheel! –  heltonbiker Feb 14 '12 at 17:46

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