# Same Ratio, Different Chainring/Sprocket Sizes Q



## Jezston (12 Dec 2011)

What is the advantage, if indeed there is any, to riding larger chainring/sprockets with the same ratio as a smaller chainring/sprocket.

For example, I have been led to believe that there are advantages to riding, say 48/17 rather than 42/15 (or even 36/13?), which give roughly the same ratios.

Can anyone explain why? I'd have thought there would at least be weight advantages to a smaller pair.


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## mickle (12 Dec 2011)

Less load on the chain and each of the surfaces it comes into contact with.


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## Jezston (12 Dec 2011)

mickle said:


> Less load on the chain and each of the surfaces it comes into contact with.


 
What effect does this have?


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## MacB (12 Dec 2011)

I don't know if there's any actual efficiency difference, one would imagine it's tiny if it exists. But all the parts should wear more slowly and I suppose a greater number of teeth engaged could mean less chance of shipping a chain.


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## gaz (12 Dec 2011)

Some people will look for a ratio that allows them to skid with lots of potential contact patches on the rear tyre.
A particular ratio may give you 3 contact patches when your leading foot is in a comfortable position for skiding, where as another ratio will give you 11.
Obviously this only applies to fixed gear and those who want to skid.


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## smutchin (12 Dec 2011)

gaz said:


> Some people will look for a ratio that allows them to skid with lots of potential contact patches on the rear tyre.
> A particular ratio may give you 3 contact patches when your leading foot is in a comfortable position for skiding, where as another ratio will give you 11.
> Obviously this only applies to fixed gear and those who want to skid.


 
That's interesting. Though apparently larger sprockets/chainrings don't necessarily give more skid patches. I plugged the figures into the rabbit gear calculator and it tells me 48x17 gives 17 skid patches while 42x15 gives five skid patches, but 36x13 gives 13 skid patches.

Personally, I prefer to use brakes anyway.

http://software.bareknucklebrigade.com/rabbit.applet.html

d.


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## Theseus (12 Dec 2011)

A bigger chainring gives the impression you are pushing a huge gear, thus gaining pseudo man points and earning the respect of lesser cyclists.


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## Jezston (12 Dec 2011)

Thanks for the info everyone! The applet linked too above is particularly interesting along with it's links to SB. I also now know how the whole skid patch thing works, which may go some way to explaining the massive raw patch on my rear tyre! (Note - Conti 4 Seasons are NOT skid friendly).

So is there an ideal 'sweet spot'? Above 48/17 are contact advantages lost? For example, any benefit of going up to 54/19 and above?


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## totallyfixed (12 Dec 2011)

A bit less wear on the sprocket if you use more teeth, it's why I ride 50x18. Scrub that, Touche has it right.


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## smutchin (12 Dec 2011)

Jezston said:


> So is there an ideal 'sweet spot'? Above 48/17 are contact advantages lost? For example, any benefit of going up to 54/19 and above?


 
The obvious disadvantage I can think of with a very large chainring/sprocket combination is that you'll need a much longer chain. Don't know how much that really matters for practical purposes.

d.


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## dave r (13 Dec 2011)

Touche said:


> A bigger chainring gives the impression you are pushing a huge gear, thus gaining pseudo man points and earning the respect of lesser cyclists.


 
Are thats where I'm going wrong, I need to ditch my puny 44X18 65 inch gear and fit something that makes it look like I'm pulling the 98 inch gear my mate is.


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## fossyant (14 Dec 2011)

Skid patches ? - get off here and join LFGSS


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## brockers (20 Dec 2011)

Touche said:


> A bigger chainring gives the impression you are pushing a huge gear, thus gaining pseudo man points and earning the respect of lesser cyclists.


I think that sums it up tbh.


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## Jezston (20 Dec 2011)

So what is the ideal chainring/sprocket combination for an approx. 2.8:1 ratio?


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## Noodley (21 Dec 2011)

Jezston said:


> I'd have thought there would at least be weight advantages to a smaller pair.


 
snarf


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## Bicycle (21 Dec 2011)

I took a massively unscientific approach to this question.

I happened to have a 50-tooth chainring with little wear and decided to use it for the fixie. So I skimmed the views of fixed-riding people in similar terrain and settled on gearing of 68-70". The chainring I already owned meant buying a 19-tooth sprocket to achieve that. Hey Presto!

I get the impression that many fixies are built up from odds and ends at minimal cost, so this may be how most chainring/sprocket sizes are chosen. I quite like the fact that my fixie works _despite_ being slightly absurd. Too much thought and planning would somehow diminish the purity.

As to the other matter: I read a lot about skid patches and it simply wasn't me. A rear brake represents little weight penalty and on the hills where I ride I'd be mad (at my skill level) to rely on my legs to slow the rear wheel from speed.

I think the skidology fascination may be an urban thing. As soon as I was old enough to buy my own bicycle tyres, skidding the rear wheel lost its allure.


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## Zoiders (21 Dec 2011)

Being able to skid stop seems cool at first

Then you twig that it's not just wearing the tyre but physically tearing the weave of the tyre apart.

These days it gets reserved for real emrgencies when the front brake is over matched, I still leg break though which is different to a skid stop.


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## dave r (21 Dec 2011)

Bicycle said:


> I A rear brake represents little weight penalty and on the hills where I ride I'd be mad (at my skill level) to rely on my legs to slow the rear wheel from speed.
> 
> I think the skidology fascination may be an urban thing. As soon as I was old enough to buy my own bicycle tyres, skidding the rear wheel lost its allure.


 
I've always had a rear brake on my fixed wheel bikes. I'm an all weather rider and wouldn't want to be mostly relying on a front brake when the road gets slippery, I also wouldn't want to find myself hitting high rpm on an icy descent whilst trying to control my speed with a front brake and legs, with a back brake and legs I can keep progress to safe levels. I am crap at leg braking and always have been, it seems that as speed goes up leg braking gets more difficult and less effective anyway.


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## tyred (22 Dec 2011)

dave r said:


> I've always had a rear brake on my fixed wheel bikes. I'm an all weather rider and wouldn't want to be mostly relying on a front brake when the road gets slippery, I also wouldn't want to find myself hitting high rpm on an icy descent whilst trying to control my speed with a front brake and legs, with a back brake and legs I can keep progress to safe levels. I am crap at leg braking and always have been, it seems that as speed goes up leg braking gets more difficult and less effective anyway.


 
That's my view too. I have brakes all round on both my fixed gear bikes and wouldn't have it any other way. I do notice though that leg braking became easier when I dropped the gear ratio from 70" to 65" but I still wouldn't like to try and stop this way on a steep hill. That's why some bright spark invented the brake caliper.


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