Chainring size efficiency

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alcatraz
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Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

This has probably been discussed but I'd just like to get a condensed recap of the ww conclusion on this.

I bought a crank without rings (compact 110 bcd) and now it's time to get chainrings.

1. Is it a good idea to use the 11t cog at all or should this be avoided? (I hear tt people dont use it because of low efficiency = choose big chainrings!)

2. Would you rather stick with a larger (heavier) chainring in order to purposely reduce the use of the smallest cogs 11t,12t? Where is the balance point between weight and efficiency?

3. Smaller big ring means greater wear on the cassette. Is this a reason to go big? Many cassettes are cheap but when you're using sram red, they are pretty expensive.

Before I was sure that a 48(even 46) big chainring would be enough since I almost never use the 11t cog. But with all this talk about efficiency losses, maybe I'm not educated enough to make this choice.

What's your take on this? How would you choose your gearing for speed?

(I'm just an amateur but I'm still interested in efficiency and would like to hear out even a tt racers opinion.)

/a

(A 48t chainring is merely 70 grams while my fsa 50t is 104 grams. Thats quite a difference.)

endershan
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Joined: Thu Jul 14, 2016 3:56 am

by endershan

You might find this site useful: http://www.friction-facts.com/

by Weenie


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SixThirteen
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by SixThirteen

More teeth, both front and back = less friction, because more teeth = bigger radius = less sharp bend on the chain. And its the bending of the chain that causes loses through friction.
Scott Foil RC10 Ultegra 12 speed / Creston 50 - 7.9Kg

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cyclespeed
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by cyclespeed

I haven't bought or seen the Friction Facts reports (has anyone on here?) Their testing seems to be quite comprehensive and accurate though.

However, they state that up to 3W savings can be had due to cross chaining and chainring efficiency, presumably the two combined.

So I suppose that means that if you are in 34-11, (cross chaining and 'inefficient' chainring size) you are going to be losing 3W compared to being in an 'optimum' gear, say, 53-15.

So the difference between 53-15 and 48-13 for example is going to be a fraction of 3W, maybe 1/2 Watt?

Really not worth worrying about. A fly landing on your arm at 40km/h is going to cost you more than that......

alcatraz
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Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Thanks cyclespeed for the reply

That covers just my question. Except the crosschaining is not of interest.

I am more interested in the difference between 48-11 and 53-13 for example. (Or any such example with similar gear ratio)

A race crankset with a larger cassette will have a weight penalty (chainrings, cassette, chain extra links). Still tt racers choose to go the 53-13 way and change rear derailleur hangar to 17t sprockets and so on. The weight is rotating mass aswell so you would think it's important to keep as low as possible.

I know changing one item or two might not do enough to consider but I wonder if doing all of them will have a noticeable difference.

I'm building a climbing bike and thus this might not be the logical setup. Still it raised my curiosity. I'm not going to buy articles to quantify the difference but if someone has a number it would be cool to know. The watt savings compared to the weight penalty.

It reminds me of the whole light vs aero dilemma. Aero is winning a lot of ground and proven faster on the flats and descents which is annoying for us ww.

Who knows if this is the way the future duraace or red setup will look like. 17t minimum sprockets on cassettes and derailleurs. 60t big chainring standard race crank. :)

/a

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cyclespeed
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by cyclespeed

I think you may find that some pro TT'ers are using 55 or larger chainrings, depending on the course.

And for the majority of these TT's weight is not an issue, you're riding mostly on the flat, and at a constant speed.

So in this rarified world of marginal gains, it may make sense to go big chainring and keep as straight a chain line as possible, but for mere mortals like us, I'd say this is pretty much at the bottom of the list of things you can do, especially as you say you like climbing.

On the rare occasion that you're in the 'perfect' gear like 53-16, and you're saving your 1/2W, you need to think about the other 95% of the time where you're just carrying around extra weight for no reason.

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BRM
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by BRM

WTF you are building a Climbing bike and are bothered by the setup of tt bikes?

You are bothering about the the balance point between weight and efficiency of chainrings.
The watt savings compared to the weight penalty.
Duh you really think that weight of chainrings matters? That the weight of an average envelope makes the difference here??

Stop the Watt savings and Aero nonsense thoughts.
The image you have is wrong. You make these things way too important.
Thanks to the marketing of the industry.

A road race bike is an optimized bike, and you can do all kinds of optimizations on all kinds of levels.
Its good to look to optimizations but you need to see the right impact of them. Many optimizations on paper and in labs with limited tests look to be effective. But in practise this is an other story. SEE IT! You need to translate them to real world conditions. There is the hick up for lots of WW members.

Your first focus needs to be on other things, the basics needs to be followed.

You need to choose chainrings based on:
The purpose of the bike, your personal power, personal effective cadence, crancklenght, chain line, whatever, etc.

Hexsense
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Location: USA

by Hexsense

BRM wrote:You are bothering about the the balance point between weight and efficiency of chainrings.
The watt savings compared to the weight penalty.
Duh you really think that weight of chainrings matters? That the weight of an average envelope makes the difference here??

You need to choose chainrings based on:
The purpose of the bike, your personal power, personal effective cadence, crancklenght, chain line, whatever, etc.

yeah, but in case of 52/36+12-28 and 50/34+11-26 both have similar min and max ratio that both will work then what would you choose?
then the question become relevant, isn't it? the different is small but it's there, and if it cost the same why not pick the better choice?


My answer for my example case is 52/36+12-28 if you consistently pedaling all the time due to very slight advantage in friction. if you pedal and stop frequently the (little) extra weight may outweigh the slightly reduced friction.

Marin
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by Marin

You almost never *need* 50-11 anyway, so stay with the smaller chainrings and cassette.

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BRM
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by BRM

Hexsense wrote:
BRM wrote:You are bothering about the the balance point between weight and efficiency of chainrings.
The watt savings compared to the weight penalty.
Duh you really think that weight of chainrings matters? That the weight of an average envelope makes the difference here??

You need to choose chainrings based on:
The purpose of the bike, your personal power, personal effective cadence, crancklenght, chain line, whatever, etc.

yeah, but in case of 52/36+12-28 and 50/34+11-26 both have similar min and max ratio that both will work then what would you choose?
then the question become relevant, isn't it? the different is small but it's there, and if it cost the same why not pick the better choice?


My answer for my example case is 52/36+12-28 if you consistently pedaling all the time due to very slight advantage in friction. if you pedal and stop frequently the (little) extra weight may outweigh the slightly reduced friction.


The best choice for me doesn't need to be the best choice for you.
The TS needs to look to his own specific parameters and make a choice based on that info.

When the TS is writing that till now he thought 46/48 is big enough, he more the less tells us he is not a person with very powerful legs. Take with that he is building a Climbing bike he probably is best off with a standard compact 50-34.

Drop the weight and friction connected to 'chainring size' nonsense. It plays no single rol here. :|
Chainline friction is a matter, not because it cost you watts but because it cost you your material. :wink:

Hexsense
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Joined: Wed Dec 30, 2015 12:41 am
Location: USA

by Hexsense

BRM wrote:
Hexsense wrote:
BRM wrote:You are bothering about the the balance point between weight and efficiency of chainrings.
The watt savings compared to the weight penalty.
Duh you really think that weight of chainrings matters? That the weight of an average envelope makes the difference here??

You need to choose chainrings based on:
The purpose of the bike, your personal power, personal effective cadence, crancklenght, chain line, whatever, etc.

yeah, but in case of 52/36+12-28 and 50/34+11-26 both have similar min and max ratio that both will work then what would you choose?
then the question become relevant, isn't it? the different is small but it's there, and if it cost the same why not pick the better choice?


My answer for my example case is 52/36+12-28 if you consistently pedaling all the time due to very slight advantage in friction. if you pedal and stop frequently the (little) extra weight may outweigh the slightly reduced friction.


The best choice for me doesn't need to be the best choice for you.
The TS needs to look to his own specific parameters and make a choice based on that info.

When the TS is writing that till now he thought 46/48 is big enough, he more the less tells us he is not a person with very powerful legs. Take with that he is building a Climbing bike he probably is best off with a standard compact 50-34.

Drop the weight and friction connected to 'chainring size' nonsense. It plays no single rol here. :|
Chainline friction is a matter, not because it cost you watts but because it cost you your material. :wink:

agreed that use case must be the first thing to consider. Only then if there are both equal in term of use then you select from efficiency (and cost, wear rate etc.)
i should have given the 48 as the example but then there is no 48/32 so the comparation of 50/34+12-28 vs 48/34+11-26 are only nearly equal in the big ring. :roll:
for 50/12 vs 48/11 then the 50/12 is better. but is there cheap 12-26 and 12-28 available for not so expensive?
i only see Dura-ace 11speed 12-28 which cost a lot.

alcatraz
Posts: 4064
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

BRM wrote:WTF....


Whats your smallest cog? How much do you use it?

If you can part with one of your cogs at either end of the cassette, you can instead change the chainring size and minimize the ratio increments of the cassette and enable you to tune your gear choice a bit better. (at expense of increased crosschaining)

The 11t cog enables me to go 75km/h at high cadence. Top speed is not the issue.

The issue is that I'm presented with a choice of chainrings. What would you do in my shoes? Go 50t big ring effectively avoiding the 11/12t cog or acknowledge that unused cogs, even small ones, are a waste and go down in chainring size KNOWING that small cogs present an efficiency penalty.

This is not a tt/pro issue. I think it's a fair question. I can go either way without added cost. I'm not trying to be a nitpick and replace perfectly ok chainrings.

/a

Marin
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Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

I'd go for a 46, which is similar to having a 50 with a 12-x cassette. You can stay in the big ring for longer & save some weight.

Incidentally, this is exaclty what I'll be doing for my Ritchey which isn't raced.

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