Big vs Small Chainring - Same Power (ERG Mode Gearing)

I think this is what we are talking about, and I do not think it is true. With high flywheel inertia vs low flywheel inertia, 1 watt does not equal 1 watt as counter-intuitive as it sounds.

It is important to remember that power numbers, no matter how accurate, are inherently “averages” over a given time, thus it is entirely possible, and likely unavoidable, that the output required to turn a 1 watt pedal stroke be different at different flywheel speeds. The principal of using flywheel inertia to maintain power output without requiring constant input has been used throughout history in industry applications such as mills and automobile transmissions. For our particular use, it has advantages like giving a nice “road feel” and smoothing out the resistance, but disadvantages such as “helping” when the goal may not be to have “help.”

Another core issue here is to remind ourselves that wattage =/= performance. Trying to compare outdoor and indoor wattages is supremely difficult, and likely impossible given how many variables there are. But when comparing indoor training flywheel speeds, I think it is pretty clear that a lower flywheel speed, while making the numbers look more depressing, leads to an improved performance.

Again, appreciate all the discussion, I love having a place to discuss these thoughts that I think only occur to someone sitting on a trainer for hours :upside_down_face:


You have eloquently summed up in a single post everything I’ve been trying to say throughout this thread. I think your comments are spot-on. Thank you!

What I mean is that if rider A can push 300w on flat, B rider only 280w, there is no way the B rider will beat A rider on a climb if they are same weight.

So in our case, small vs big ring, I am almost sure that those who will put more watts on small ring, will still stronger on big ring, and it’s true on other side as well (not sur if I am clear, sorry, I’m French). At my camps, It’s very rare that a rider beats a rider with an higher power ratio on the Hill Climb TT (no drag or strategy)

So I’m surprised by this thread as it doesn’t match my experience on kick snap wheel on trainer, controlled by stages PM.

I have somewhat randomly alternated big and little ring based on mood, including for ramp tests, and I really can’t see a meaningful difference. I haven’t done back to back ramp tests, but during times where I’m expecting to be fairly flat vs prior test, I get the same result within a few watts. No pattern I can see based on flywheel momentum but I’m going to start paying more attention to this.

It sounds like this puts me very much in the minority. I have done a decent bit of small ring indoor rides and often climb at higher cadence with easier gearing so maybe things just match up with that training? Whereas for someone that never climbs perhaps it’s more normal to see the big difference?

I’m just really surprised by reports of 30-40W differences. I’ve never seen anything like that.


This is a recent development in this thread. Early on, most were settled on “whatever difference there is is in the margins.” I don’t notice any difference in HR, RPE, or anything else meaningful. I train in the small ring now, started in the big ring. I think the small ring gives a closer approximation to the road for the things I want to train for, but 30-40W difference? No. No way. Placebo if anything, IMO.

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30/40w is around 10% for me, might be more difficult to see for someone at 200w FTP.
I always have a FTP between 330/340 on small ring while I often race more an hour on Zwift (so on big ring) around 360 average. On road, can race 4 hours at 340w NP or climb 40’ at 385 which would be both impossible with an FTP of 330/340. Zwift (big ring) numbers look more « real », that’s what I mean.
Will do a test on big ring in 10 days, will see.

My FTP was 270 when I did the comparison. Interested to see what you find this time. Seems improbable based on the mountain of other anecdotes and my personal experience.

Here are some data of the last training camps I organized. This is the result of a TT clilmb I organize on fourth day. Let me give you more details:

  1. Atheletes are tested on the first day, on trainers (Wahoo Kickr 2016 and 2018). They all had one of our Stages powermeters and used 34x19 as I asked them (small ring to reduce the noise).
  2. On first day (after the test), second and third day, they have been training on the road : 2h20 + 4h30 + 1h50. They did a lot of climbing every day (2% avg.). Just want to mention that they accumulate fatigue days after days during the training camp.
  3. Took them to Sa Calobra on 4th day, but to reach the bottom of the climb, they had to ride 83km with 1920m of elevation (three long climbs of 25 minutes).
  4. They performed the TT alone, without dragging. Every riders started with a time difference. So nobody paced for them. Goal was just to go full gas!
  5. The “FTP HOME” is the value they have at home. Four of them use TR but on different trainers. I asked them by Whatsapp yesterday if they use small or big rings at home. They are all on the big one…

So I don’t know which one is true, but to me, their “home” value look more realistic compared to their performance on the Sa Calobra climb.

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Just did a test on 52x12 (I am impatient lol). Went from 333w (5th of November) to 348 without pushing myself to the “dark zone” today (I have a four hours ride to come now). Not very fresh this morning, since I rode everyday this week, but yes, there is a massive difference. Will do another one on 10 days, with a day off before. Will see…

*** EDIT ***
I understand now why I was using the Kickr on small ring. Because on 52x12, it’s getting really noisy above 320 watts! Might not be a problem for someone with lower FTP, but doing 2 hours intervals of sweetspot at 330/340 watts seems impossible. So I will probably keep the small ring for myself (despite not being able to get right numbers on TrainingPeaks) but will probably test athletes on big ring now. Seems more accurate.

Do you have any data on a trainer other than the kickr? The reason I ask is that the kickr is (or at least was) generally known as one of the trainers with the worst spiral of death tendencies (resistance increasing quickly when the cadence drops).

It’s possible that this effect is at play with the kickr in small ring. When the kickr senses the crank angular velocity reducing towards the top of the pedal stroke (which it does a lot more in small ring vs big ring), it increases the resistance - and does this more than real world conditions on a climb. Hence these “excessive” variations of resistance over the course of the pedal stroke are more fatiguing that real world climbs (and more fatiguing than big ring).

Just a theory, but on this and other threads, the kickr is the trainer that is mentioned most in connection with this topic.

No, and I am 99% sure that on that list of athletes, none of them use a Kickr at home. Regarding velocity, I thought Kickr (and other powermeter by the way) were managing intensity depending of the data sent by TR through iPad or Computer, no ?

You have data showing kickr small ring under represents their FTP. Would be interesting to know their small vs big ring FTP on their home trainers.

Yes, this is true - trainers get their target power from TR. but how the trainer reacts to control actual power vs that target is dependent on the control algorithm within the trainer, and can vary between trainers.

Note: powermatch may be different, but I don’t fully understand how powermatch works, so won’t comment.

I do! Can not ask all of them because it would also admit that my system is not good yet. But for two on that list, I found on Trainer Road that :

  • FCX did 342 watts 4 weeks before
  • PLT did 237 watts 6 weeks before

I know it’s hard to compare different set up, powermeters, etc. But my experience of this morning and several similar comments here push me to think that there is something to explore here.

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We’d all pull our hair out if we really tried to get to the bottom of things! I think the big variables are:

  1. Individual rider physiology
  2. Trainer control algorithm
  3. Trainer/PM power measurement algorithm
  4. Trainer flywheel moment of inertia / weight
  5. Plus maybe some rider psychology also

Good luck figuring all those out!

I think some other conclusions could also be possible from this data -

  • FTP right after travel and arriving at camp is not as good as home test for most people (reasonable expectation, could depend on individual circumstance that we don’t know)
  • Some are much better at climbing outdoors than they test indoors in any scenario - e.g. rider 5; more generally, outdoor motivation and performance for most of them relative to indoor FTP tests is higher (1,4,5) - (I think most would say very typical observation)
  • Rider 6 is very consistent and shows no meaningful bias IMHO

Sounds like it’s more of a mixed bag person to person how much this affects them, which usually ends up being the answer to everything!

I agree with you. It’s not easy to make conclusions of this, that’s why I will try to experience by myself to find the best solution for further customers.

Regarding the testing protocol, travel has probably a (negative) impact, but on the other side :

  • I always ask them to do nothing on Friday morning (arrival day) and very light on Thursday to be fresh on Saturday morning for the test. I wish I could take two days off before a test lol
  • Travelling to Mallorca is pretty fast. Most of the time, people fly 1 up to 2 hours, not more
  • Performing a FTP with people around you increases motivation I think.

My personal test of this morning is already convincing me (went from 333 to 347 without pushing too much today).

For what its worth, my indoor and outdoor FTP is the same when using big ring on wheel-off Kickr 2017.

Not the best example… yesterday I did a 6-min climb up 10% grade in 36x32 gearing (needed 34x34!!!). Ridden at threshold by feel and I left ClimbPro on Garmin 530 display. For reference LTHR is somewhere between 158-161bpm and max is 175.

Definitely could have kept going for 20-40 minutes, not saying that is a great example as its only 6 minutes but it is consistent with previous long climbs at threshold.

On both flat road and climbs, my indoor and outdoor FTP seem very consistent. TR PowerMatch inside using Stages LR power and Kicks 2017 wheel-off trainer. Right now on trainer I’m using 53x19 or something.

I’m definitely going to keep watching this thread and will eventually test this a little more carefully myself as well, because I still haven’t done a perfectly controlled test either.

The funny thing is my only real prior motivation for one vs. the other was that the big ring and higher flywheel speed gives me a more realistic “mileage” estimate consistent with my outdoor riding - while the smaller flywheel is quieter. But now I’m going to explore this a bit more carefully on the power.

By the way, I’m making my first trip to Mallorca in January - flying to France for work via Barcelona, and when I saw flights to Mallorca for $15, figured it was a no-brainer to do a week layover. Looking forward to burying myself in cycling mecca!

:+1:t3: So 3 of 4 match (climbing, flats, big ring). Now you just need to test little ring inside :grin:

Little ring on trainer has been mixed as stated earlier in thread. Right now I’d bet ramp test would give lower FTP (ramp is max aerobic power aka MAP test).

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