Originally Posted by
pdlamb
The big assumption here is that all other things are equal. Once you start looking carefully, most (not all) tire models start picking up sidewall stiffness as the width increases, usually between 25 and 32 mm wide. That's why tires wider than 25 or so often have higher rolling resistance than narrower tires. The exceptions are usually pricey.
I don't know this to be generally untrue, but there are definitely tires available in multiple widths that do not follow your description. I am a big fan of Panaracer Pasela tires, which are not expensive (although not easy to find these days), and the larger widths are definitely made with the same construction as the smaller widths. To be fair, there just aren't that many tires made in the same model that come in widths from below 30mm to above 30mm, and lightweight construction wider tires are more rare than lightweight construction narrow tires.
ANyhoo, here is a rolling test of one particular model available in many widths. They even publish stats like sidewall and tread thickness, and the wide tires seem to be very similar, if not made the same as the narrow tires. The widest tire has the lowest RR and the narrowest tire has the highest RR.
https://www.bicyclerollingresistance...000-comparison