Big or small chainring (engineers?)

[NotSoBigBen]

Pondering on this question for a while ....

As a 53*28 is the same gearing as a 39*20 and there is some overlap in gearing would it be better to use the smaller chainring when possible? Knowing that you will essentially be pedaling at the same cadence for the same speed.

Now the 'engineering' part ... I'm thinking that the leverage on the smaller chainring is better considering where the chain is on the length of the crank (closer to the center). Not sure if the now 'lower' position of the chain on the cassette would have an influence?

Now I guess the real issue would be let's say you're riding into a headwind for some time or you're looking at a long day/night in the saddle, would there be enough 'marginal gains' to even bother ...

Ok so now my brain is all confuddled but hopefully it makes sense to those engineers and others interested in engineering that could set my mind at ease 🤔

[The Ouzo]

From my limited reading it seems to be agreed that the bigger chainring offers less wattage loss through the chain as the links are not bending to such a tight angle. 

[AkwA]

Can imagine there is a diff, but can’t imagine that it would matter at all, as far as I know, wattage lost in a well lined chain is around 7-10 watts max

[DieselnDust]

Personally and after reading so many of those wattage savings reports I believe it’s all marginal gains. 
the torque differences between the gearing is going to be marginal although there is an advantage to the smaller chain rings that off sets the additional but very small friction force increase.

the gear combo that maintains the straightest chain line will be the one that is most efficient and that sounds like the small chain ring and the 20t.

as long as the chain is lubricated friction losses are very small

[Fred van Vlaanderen]

3 hours ago, ouzo said:

From my limited reading it seems to be agreed that the bigger chainring offers less wattage loss through the chain as the links are not bending to such a tight angle. 

Agree

[NotSoBigBen]

Thanks guys, so I understand that efficiency is more important than the very marginal benefits from my leverage theory. 

Dammit thought I was onto something there 🤨 

[NicholasB]

If you go with a small chainring, you might find yourself in your lowest gear most of the time which could cause heavier wear on your cassette.

Edited May 21, 2022 by NicholasB

[One Speed Wonder]

More teeth on the chain shares the force better so less wear too.

[Frosty]

53-28 would be too cross-chained for me, so I would prefer to ride the smaller chain ring and use the gears closer to the straighter chain-line.

A steepish descent followed by a steep ascent challenges one to ensure a dropped chain is eliminated when shifting from 53 to 39.

[MORNE]

4 hours ago, DieselnDust said:

Personally and after reading so many of those wattage savings reports I believe it’s all marginal gains. 
the torque differences between the gearing is going to be marginal although there is an advantage to the smaller chain rings that off sets the additional but very small friction force increase.

the gear combo that maintains the straightest chain line will be the one that is most efficient and that sounds like the small chain ring and the 20t.

as long as the chain is lubricated friction losses are very small

Granted my bike us 1x with a 42T in the front..but i love 19T in the back so much for how quiet and smooth it us that i ride it more on purpose haha. same reason why i have 19T single speed cogs😅