Originally Posted by
tomato coupe
As stated by Duragrouch, the chain essentially "digitizes" the drivetrain, so any two 16 tooth cogs will give you the same rollout. Any difference in measured rollout comes from the tire circumference.
And both of you would be wrong. The chain doesn't "digitize" anything. Toss on 4 different 16t cogs from different brands and see what the results are, high end brands will give you more consistent results, cheaper brands less consistent. For a deeper dive look into bmx fractional gearing which over emphasizes the differences, but when you have kids who are trying to get that 1/2" longer gear inch a 16 1/4 cog can do the job. There's no 1/4 tooth, they've just cut the valleys shallower to add the difference. Example,
https://identifybmx.com/products/5-bolt-fractional-gear BMXers get deeper into it than any other sport and the chain isn't digitizing anything. The same issue exists accidentally when trying to keep a kid's bike within an allowed limit. When they say 19' 10 1/4" they really mean it. Absolutely, tires make a difference, but so does the rest of the parts, it might not even be a quality difference but simply that different manufacturers have different standards on where the valley sits, but that's what really determines the real diameter of the cog.