Originally Posted by
Mtracer
The majority of the difference in power you are seeing cannot be from the rolling resistance of the tires. At those speeds, the entire rolling resistance would be on the order of 30 W. So, the difference you would get from tire width would obviously be a fraction of that.
Yep.
The reality is it is very, very difficult to make these types of comparisons in the wild. Especially with single runs at different times under what will always be different conditions to some degree. It takes many runs to be able to make statistically significant comparisons.
Not always, though it depends on what you consider "many." If you do it right and you're lucky, maybe three runs of a couple of minutes each, for each tire combo. But it's easier to do indoors on rollers in controlled conditions, so I completely understand that people do it that way. (It's even easier than that to forego testing and instead read bicyclerollingresistance.com)