FTP and chainrings

Today was a good Ramp Test day, but one that got me thinking: is there a correlation between FTP and chainring size? Whether scientific, or ‘TR Podcast’ scientific.
I get there will be factors, such as local terrain, weight and preferred cadence (and ego?)
I’m just interested in what others use.
FWIW on my road bike I use a compact, TT bike is a semi with an FTP of 263W at 58kg.

There will be a direct correlation of increasing your chainring size as your FTP goes up as you will start to spinn out / need a bigger gear. Subsequently, someone with a lower FTP will go for smaller chain rings as they will simply have a hard time pushing through say a 52+ chainring.

I am however curious whether on a FTP test day (ramp test for example) you would get a better result with a specific chainring (be it a larger one with a lower cadence or a smaller one with a higher cadence).

Any science nerds out there with possible exact math? :slight_smile:

Edit: currently on a 1x raodbike setup, 50 in the front and a 12-26 in the back. Will be changing to a 52 in the front soon as I am starting to spin out myself

If you are on a smart Trainer and in ERG mode, Chain ring size only affects the speed of the Flywheel. Also if your cadence is 90rpm ERG will just keep ramping up every minute as normal. It is true bigger chain ring will require more Torque to turn over and hence higher force. But Power is power.

Probably when looking as a whole - as you hint it’s not as simple as that (I am talking outdoor riding only)

There should be a correlation between your gears and your personal optimal cadence range, the terrain you ride and your output.

I am not a ‘powerful’ rider in term of torque and am happier pedalling at 95RPM than 75RPM. At 95 my HR is lower than 75RPM, as is RPE for any particular wattage. A friend is the exact opposite, a torquier rider who’s HR shoots up for a any given output done at over 90RPM, who blows quickly over 100RPM and who’s natural cadence is 75-80RPM.

For the same course he would benefit from a larger gear. I would want a smaller gear. We both may be producing the same wattage (and indeed do when you compare - wattage, HR and power are often near identical but with a ~10RPM difference).

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Tacx Neo 1, 2 and T (& ? Bushido) use variable virtual flywheels. I don’t know whether they adjust the size of the flywheel with different speeds or powers in ERG mode.

With conventional fixed flywheel masses (assuming same rear gear) the flywheel would spin faster so it might help smooth out your stroke a bit. Doubt it’d make much of a difference though.

You can definitely feel the change in Virtual flywheel size on my Neo 2 when simulating a climb but then it can go from big to small all of a sudden, rather than in steps.

I think I did ask Tacx what they did with the virtual flywheel size in ERG mode and they answered a different question. In fact, I’m sure I did as I can remember guessing that they assumed a fixed 1%.

The Virtual flywheel size does vary with rider weight (atleast in slope mode) though. You could potentially lie in the Tacx app and see if changing weight (and hence flywheel size) makes a difference. I’m too lazy.