Odd teeth

[jimlews]

A very simple question for the forum cognoscenti.

Why do chainwheels usually have an even number of teeth ?

My intuitive notion is that an odd tooth count would tend to even out the wear of the components of the drivetrain (chainwheel/chain/sprockets)
Is my notion correct ?

[Jdsk]

A very simple question for the forum cognoscenti.

Why do chainwheels usually have an even number of teeth ?

My intuitive notion is that an odd tooth count would tend to even out the wear of the components of the drivetrain (chainwheel/chain/sprockets)
Is my notion correct ?

"Does the number of teeth of a chainring need to be prime?":
https://www.cyclingforums.com/threads/d ... me.300428/

Jonathan

PS: Prime number periodicity in cicadas:
https://en.wikipedia.org/wiki/Periodical_cicadas
and 2024 is a 13 and 17 year!:
https://www.nbcnews.com/science/science ... rcna134152

[mig]

not sure that there is a usual teeth count....?

chainring and sprocket teeth count become more important if you ride fixed over distance in terms of component wear.

[TrevA]

Back in the day, a standard road double would be 53/39, both odd numbers. More recent chainsets tend to be 52/36 or 50/34, but SRAM have a 35 tooth inner ring on some of their chainsets.

[cycle tramp]

A very simple question for the forum cognoscenti.

Why do chainwheels usually have an even number of teeth ?

My intuitive notion is that an odd tooth count would tend to even out the wear of the components of the drivetrain (chainwheel/chain/sprockets)
Is my notion correct ?

Most of the 1x chain rings have even teeth simply because it's the only way you can get 'thick/thin' chain ring teeth which help the chain stay on the chain ring ...

Other than that there is no reason and as chain rings get larger you can certainly find more odd numbers - this is due because the difference of a single tooth is more likely to be felt in high gears rather than lower ones...

[Jules59]

I run 50/33 chain rings

[Brucey]

Back in the day, a standard road double would be 53/39, both odd numbers. More recent chainsets tend to be 52/36 or 50/34, but SRAM have a 35 tooth inner ring on some of their chainsets.

aye but before that they were always 52-42, so both even. Chains do wear unevenly, so if you run a chain (on a single chainring) to the bitter end, it really matters if you have even or odd teeth. Otherwise, meh, not so much. Anytime you have more than one chainring, the wear tends to even out, even if the tooth count is even (if you see what I mean).

[Cugel]

Back in the day, a standard road double would be 53/39, both odd numbers. More recent chainsets tend to be 52/36 or 50/34, but SRAM have a 35 tooth inner ring on some of their chainsets.

aye but before that they were always 52-42, so both even. Chains do wear unevenly, so if you run a chain (on a single chainring) to the bitter end, it really matters if you have even or odd teeth. Otherwise, meh, not so much. Anytime you have more than one chainring, the wear tends to even out, even if the tooth count is even (if you see what I mean).

An' before that they were 49/46 - I had such a thing on me Coventry eagle, got in 1960 and changed with a twitch-rod located on the RH side of the seat tube, that one reached down and pulled to lift the chain from 46 to 49. You could change it the other way with a press of your calf agin' the twitch-rod.

Four cogs at the back: 14-17-20-24 as I recall. The idea was that the chainrings provided intermediate gear ratios atween the main rear cog ratios. In practice, it tended to get left in the 46 most of the time. Even then I was a spinner not a heaver, me!

[mattheus]

Back in the day, a standard road double would be 53/39, both odd numbers. More recent chainsets tend to be 52/36 or 50/34, but SRAM have a 35 tooth inner ring on some of their chainsets.

aye but before that they were always 52-42, so both even.

Beat me to it!

Also, apparently the Grand Tour pros used to have a thing - probably a superstition really - of preferring either odd OR even tooth counts for climbing mountains. Not sure what killed this. Or maybe they just don't talk about it publicly now ...

[rogerzilla]

Fixie/SS/hub gear riders would do well to choose chainring and sprocket combinations that spread out the wear, since they are locked into a particular periodicity. Prime numbered chainrings are good, although you have to watch that the chain links aren't exactly twice the chainring teeth. Sod's Law says they often are.

[Jdsk]

The requirement for equal engagement of teeth, links etc isn't being odd or being prime, it's being coprime:
https://en.wikipedia.org/wiki/Coprime_integers
https://en.wikipedia.org/wiki/Coprime_i ... plications

Jonathan

[mattheus]

Fixie/SS/hub gear riders would do well to choose chainring and sprocket combinations that spread out the wear, since they are locked into a particular periodicity. Prime numbered chainrings are good, although you have to watch that the chain links aren't exactly twice the chainring teeth. Sod's Law says they often are.

This is one of the fun little things that makes fixed so intriguing to me! One day ...

The requirement for equal engagement of teeth, links etc isn't being odd or being prime, it's being coprime:
https://en.wikipedia.org/wiki/Coprime_integers
https://en.wikipedia.org/wiki/Coprime_i ... plications

Good work - I didn't know the name for this!

Is it also the case that all real world setups with prime chainrings will be coprime?


(These are probably the only primes relevant to chainwheels: 29, 31, 37, 41, 43, 47, 53, 59 )

[Jdsk]

...
Is it also the case that all real world setups with prime chainrings will be coprime?


(These are probably the only primes relevant to chainwheels: 29, 31, 37, 41, 43, 47, 53, 59 )

What's the range of rear sprockets... all less than 29?

Jonathan

PS: Someones's going to mention jockey and guide wheels... ; - )

[mattheus]

...
Is it also the case that all real world setups with prime chainrings will be coprime?


(These are probably the only primes relevant to chainwheels: 29, 31, 37, 41, 43, 47, 53, 59 )

What's the range of rear sprockets... all less than 29?

Jonathan

PS: Someones's going to mention jockey and guide wheels... ; - )

Yeah, I assumed that noone would go that big .. and 29x29 would be the only problem case. DOES anyone run 1:1? Happy to be proven wrong

(I'm not touching the jockeys/guide wheels problem ... )

[Brucey]

In case anyone else's brain is quietly melting, it is as well to remember that none of this really matters unless something is worn. Before then, it is just number theory.