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Let have these two combinations of chainring/cog. Both for 100 rpm, have almost same speed (and we can of course find cases where the speed matches exactly, but this is a quick example).

50x19-->20.58 km/h
34x13-->20.50 km/h

My question is, (ignoring the small difference in speed in this particular example) is there any difference in these 'equivalent' combinations? Can we -on the bike, experience any difference? or is absolutely impossible to tell?

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    try 55x22, 50x20, 40x16, 30x12
    – Noise
    Jul 1, 2022 at 12:47

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50:19 has less drivetrain friction because the chain doesn't have to bend around such tight angles. This means it will be slightly easier to maintain the same speed in that gear combination.

This article is a good read if you want some more insight: https://www.velonews.com/gear/gear-issue-friction-differences-between-1x-and-2x-drivetrains/

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    It's nice in theory, but on a singlespeed bike, is the difference big enough to notice? Are there other advantages of one over another?
    – Noise
    Jul 1, 2022 at 12:49
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    Assuming a typical gear setup, the 50:19 will have less lateral chain deflection, which is another contributor to mechanical losses. I don't think you'd notice the difference when riding.
    – Adam Rice
    Jul 1, 2022 at 12:59
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    @JoeK i'd say its probably borderline if a rider could notice the difference in a blind test. looking at a ~2-3% saving in power. I guess in theory the 50:19 should also wear better too because spreading the load over more teeth.
    – Andy P
    Jul 1, 2022 at 13:00
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    In the given example ratio, I think the wattage delta is ~3W at 250W input. I believe the delta should scale about linearly with wattage, and 250W is high speed. So, I think most riders would not notice immediately in daily riding. That said, not immediately noticeable is different from meaningful, and this is essentially free speed and increased chain wear that you’d be passing up.
    – Weiwen Ng
    Jul 1, 2022 at 13:42
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    @AndyP: the number of teeth the load is split over is probably only 2 or maybe 3 in both cases. The links near where the chain leaves the cassette will be extended by the tension in the chain leaving the rest at almost no tension.
    – Ross Millikan
    Jul 1, 2022 at 14:06

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