Chain Ring diameter.

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tovetune

Regular
Now retired and wishing to get back cycling after many years without a bike I'm amazed at the changes made to bikes over the years, at the moment I'm thinking of a gravel bike and whilst researching what's available one thing I've noticed is that some bikes have much smaller diameter chain rings (and consequently larger cassette rings) than what was 'normal' when I last cycled regularly. What is the reason for this and are there any benefits over larger diameter chain rings?

Thanks in advance.

Mick.
 

presta

Guru
Triple chainrings have gone out of fashion and been replaced by twins (or even singles), that means that the largest ring had to get smaller, and the smallest larger. The reduction in the largest ring means that top gear became lower, because there's little scope for a corresponding reduction in the size of the smallest sprocket, and the increase in size of the smallest ring meant increasing the largest sprocket to the size of a dinner plate in order to maintain the lowest gear ratio.

If you ride with a 22 ring and 11 sprocket instead of a 44 ring & 22 sprocket for example, you still have the same gear ratio, but the tension on the chain is doubled, increasing wear. The increase in wear on the teeth is even greater, because the load has been doubled and there are half as many of them to share it.
 

Ian H

Ancient randonneur
Sprockets now go down to (up to?) 11 or even 10. There are derailleurs that'll handle ludicrously wide-ratio cassettes. Few people outside racing need even a 50t ring. Low gears for climbing are in fashion. Those who used to mock riders with a 'granny gear' now use the same or even lower ratios with two or even one chainring.

Personally, I still use a triple with relatively close-ratio cassettes because I dislike large/huge jumps between gears.
 

Dogtrousers

Kilometre nibbler
smaller diameter chain rings (and consequently larger cassette rings)
The larger cassette sprockets are not consequent to the smaller chain rings in that they don't compensate for them. Making the chainring smaller results in a lower gear, as does making the sprocket bigger. They both result in lower gearing. Put together they reinforce each other and give super-low gears.

There are two factors at work.

One: The trend for reduction in the number of chainrings - fall in popularity of triples (some of which have a very small smallest ring, but it's on the inside so you can't see it) and introduction of 1x single chainrings. Arguably this trend was manufacturer driven in order to shift new kit.

Two: An overall lowering of gearing - or more specifically, lowering of the bottom gear. A reduction in cycling machismo that tough cyclists ride super high gears.

Put these trends - fewer chainrings and lower gearing - together and if you want to get a really low bottom gear you need a teeny tiny chainring and a massive big sprocket. But if you look at these cassettes they also have a teeny-weeny 11 or 10 tooth smallest sprocket to give a usably high top gear.
 

Cycleops

Legendary Member
Location
Accra, Ghana
What is the reason for this and are there any benefits over larger diameter chain rings?

Thanks in advance.

Mick.
Fashion, that’s all. Might make assembling bikes at the factory slightly cheaper. The manufacturers will tell you it’s ‘simpler’ as you don’t have a front derailleur or associated shifter. Believe what you will.

Don't forget you’ll have bigger gaps between the gears as opposed to say a triple chainset as you’ll have fewer gears.
 
OP
OP
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tovetune

Regular
Years ago before the days of the internet I would have had to go to my local library, bike shop or asked a knowledgeable cyclist to find the answer to question I posed today, all of these options would have taken time. With the benefit of the internet and forums such as this I've been able to get informative answers in a very short time - thanks to all who contributed.

Regards, Mick.
 
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