Drivetrain efficiency - does chainring size really matter?

Since the discussion of chainring sizes, and their efficiency has flooded other threads, I would like this thread to become the place to discuss this. The origin of discussion accrues from the smaller chainring sizes and the 10t cog of current gen SRAM drivetrains, vs Campa and Shimano maintaining a 53/39 and 11t cassette for the 12x generation.
A few links on this discussion:

From what I see here, the difference of a 50/37 vs a 53/39 with similar chain line should be measurable, but very low. A little too Low for people calling it an engineering fail. It is not like a smaller chainring doesn’t have any advantages.
But: please discuss!

I PERSONALLY don’t think it’s an engineering fail, but based on where and how I ride with my 52/36 x 11-28 the SRAM gearing isn’t really speaking to my needs because I don’t have any deficiencies in my gearing. The only nitpick I have is the 15-17t jump on the 11-28 cassette, but that’s not enough to make me go to SRAM

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This is how I go about choosing a chainring for TT, where I have 1x SRAM AXS system.

The are between the green is the middle two cogs and the between the yellows is still very acceptable. This is at 92 cadence (average of my last TT).
My average for the last event was 44kph, but with extended (headwinds, false flat) periods below 40kph.
For optimal chainline, I‘d need a bigger chainring (56 preferably)

However, a sub optimal chianline (first example) might be beaten out by the fact that I can go sub 20kph at the end, when there is a 5% climb of 2 minutes at the very end of the TT…
This probably will always be the trade off, and I am always on the side of, I rather pedal less than optimal for the majority of the race, but can properly ride all of it (even the steep bits), than having a perfect chainline 95% of the time and no proper gear for the remaining 5%.

Why don‘t you use the SRAM 11-28 Cassette? It‘s compatible with Shimano 11s and has a 16T cog

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I don’t like the gear spacing for the climbing gears as much as Shimano’s which have a smaller jump, being able to really fine tune the gear I want on a climb outweighs any slight increase in watts I need on a flat where I end up jumping into the 15t

SRAM. - 11,12,13,14,15,16,17,19,22,25,28
SHIM… - 11,12,13,14,15,17,19,21,23,25,28

I don’t really think about drivetrain efficiency losses since they are pretty insignificant aside from aggressive cross-chaining and a dirty drivetrain

Marginal gains podcast talks about lost watts on the smaller cogs. So If your running smaller then a 50 and using the 11/10/9 your wasting some watts. Think the sram axs app can help you see the time in each gear and determine if your throwing away watts.

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A larger chainring/ cog combination is more efficient, I don‘t think anyone doubts this. For a super flat TT, a super flat road race or anything on the track, its best to choose a 100T Chainring with a 28T cog…
However, the difference between 53/39 and 50/37, both with the same chainline is around 1-2 Watts at 300W+.
My argument is, that the smaller chainring, paired with the SRAM AXS cassettes offers a very wide range, with very small gears at the low end. This to me is often more important than saving a Watt at threshold.

I have the feeling that the vast majority of road cyclists runs out of gears more frequently, than having problems from losing a watt or two. I am always surprised by how average joes tell me they have now upgraded to 11-28 for their trip to the alps…
From this brutal over gearing the efficiency loss is a lot more than two watts…

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I think anything after 56tooth you lose aero at more watts then you will gain based on the marginal gains podcast i listened to.

I tend to think a 28 is not enough gear for most cyclists.

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I guess it depends on the terrain they ride in, but there’s very few places where I want more than a 36x28, and I don’t ride them enough to give up the smother transitions in the cassette everywhere else. Also seems like a lot more bikes come with 50/34 cranks now

Marginal gains wise I was reading something about those OSPW systems and how they create more drag than they save in efficiency in most cases, thought it was interesting

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I’ve got the worst of both worlds - pancake flat with strong tailwinds, and as many 3000-5000 foot climbs as I can manage.

I would love to see someone to labtest a lot of these claimed 1w gained items.

100% terrain dependent. 2 weeks ago I did a ride and people running a 28 were walking the hills due to sand on them, it was a road ride also. I was able to run 11/34 on that ride and had no issues running 11/34 on a group ride with a 15mph tail yesterday. If i was doing a flat crit, road race im running the 11/28 though

I don’t think anyone can really feel single digit improvements. My latex tubes apparently save 4-5w per tire and the only thing I can feel is a smother ride, it’s not like “omg this feels so much faster than butyl”.

Always get a chuckle when someone on a group ride talks about how much faster their bike is having ceramic bearings and integrated cables :rofl:


I think focusing on the losses at the chainring is looking at the wrong end of the chain - the concerning part with going to smaller chainrings is the use of 10 or even 9 tooth cogs - this is where the losses are more likely to come from.
I recall reading that a pro team on AXS had the 10 cogs locked out and not used, and I think this went along with larger pro-only chainrings. For most people the differences are likely immaterial in practice, but for pros a 3ish watt difference is not something that they will be happy about.


Depends on the use case. If it’s a TT bike that’s going to be used for mostly flat to rolling courses, then a) every watt counts and b) you don’t need a lot of gearing range. So going with a big chainring that enables you to keep a straighter chain line and use a bigger cog at the back makes sense. If it’s a training bike that you’re not going to race on, and/or you have a high degree of confidence that your ability to lay down power at >35mph is never going to be a deciding factor in your race, then going with a 1x with a smaller chainring and a 10T for simplicity 'one less derailleur = one less thing to go wrong) makes sense.

Personally I have 1x with a big chainring on my TT bike, I don’t do hilly courses on it. I have 52-36 and an 11-28 on my race bike because at race pace that’s enough for everything I race on (and funnily enough re your message in the other thread, I have been up the Mortirolo on that bike while mostly seated apart from stretching my lower back!). I have 50-34 and 11-32 on my winter/training road bike, and that’s what I take with me if I go away on bike trips to the mountains where I want the ability to do long climbs at a more comfortable pace. Would certainly consider a SRAM 1x setup on that bike, just wasn’t available when I bought it.

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Or how about ‘clipless pedals will make you about a mph (or kph) faster!’ I’ve tested that 9 ways to sunday. If clipless pedals make you faster it’s hard to measure.

I once crammed a couple pounds of clay into the trough of a set of mavic open pro wheels to see if weight at the perimeter of the wheel made a big difference. Nope. (although for sure it FEELS different even if you’re blinded to which wheelset you’re using) But I will say this: it is true that it’s a major PITA to scrape two pounds of clay out of a wheelset.

re: latex tubes for several years I would say I couldn’t tell the difference in ride feel between my wheels with butyl tubes and my wheels with latex tubes. Then I tested them & really road the same set up back-to-back…as you mention, you sure can feel the difference. But if I rode, changed the tubes, had a nap, and road the new tubes the difference was not noticeable. My tube detecting ability needs to be calibrated regularly, I guess.

One other thing I was excited to test that turned into a bust: cranksets. Ha! No crankset makes a difference as far as I can tell! I tested the flexiest chinese carbon crankset on the web vs DuraAce. No measurable difference. I guess that’s why the industry reports x.xx% stiffer and not x.xx watts saved.

But the difference between big ring/little cog for 53/11 vs something like 48/10 is real. And it’s measurable (and significant!). You can mess around with some single speed cogs on your smart trainer and see the difference.


I can feel a little more resistance if I pedal the. Ike with my hand on a stand, but not while riding and putting out any kind of power at all. Same goes for my 1x EAGLE, yea the 50t creates some wild looking cross-chaining but not something I can feel riding, only if I spin the cranks by hand.

I think if you blindfolded someone on a trainer, put in earplugs so they couldn’t hear how crosschained they are, you did the shifting for them and had them pedal, the vast majority would not be able to feel any efficiency loss through their legs, let alone if they are on a SRAM 1x or Shimano or SRAM 2x or whatever. This isn’t to say this stuff doesn’t matter, marginal gains add up, and I still enjoy reading this stuff to understand the concepts even if I think the argument is a moot point practically.

I’m impressed with your dedication!

Yep terrain is key. I live in the flat lands and only need to use the small ring for “hills” on strict Z2/recovery rides. I use a 53t big chainring and used to only buy lightly used 11-23 cassettes because they were super cheap. The small jumps are a very nice feature. I’ve slightly enhanced my range in the last year going to 11-25 as I occasionally venture to some bigger “hills” around 30 miles away.

I have now ridden sram AXS for over 20,000km and according to my sram app have spend 2h48min in the 10T… much of that was during hard intervals on descends and on really steep descends… not sure how much this 3 Watt waste has been felt considering this is during 800+ hours of riding.

Regarding the pros not being happy with a 3 watt loss. They choose shallow wheels for most races, round bars for most races and climbing bikes for most races. They happily take a 10 Watts+ loss for feeling a little more confident.