Originally Posted by
Russ Roth
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.
Or probably the same for new vs worn. But as folks are trying to convince you, there's no way it can't average out the same; the only way the ratio of crank turns to wheel turns can vary from the ratio of ring teeth to cog teeth is if the chain can jump over teeth.
The only possible variable which can affect rollout (over a sufficient distance to allow discrepancies introduced by roller/tooth slop and chain wear to average out) is the tyre. The effective circumference of the tyre is going to vary by nominal size (obviously), brand, pressure, temperature, bike and rider weight, tread wear and any damage to the carcass, and possibly variation in diameter of the bead seat on the rim if clincher, or glue buildup on tubulars, which might also vary slightly in size from rim to rim.
Think about it. Every turn of the crank is x number of teeth, every turn of the wheel is y number of teeth, regardless of the fit of chain on cog. At the end of the day, the only way it can't add up is if the chain jumps. If the distance used to measure rollout is too short, the measurement will show noise from poor drivetrain tolerances.