the 30mm prob rolls faster than the 28mm - and a 32 might roll faster than both
unless you get carried away and reduce pressure too much
but of course there is a weight increase as you go up in size
( see chart above and link below )
https://www.bicyclerollingresistance...000-comparison
.
the issue i have with BRR (which i love reading!) is that the differences are so tiny in this kind of tire (a few watts max) that they’re totally swamped by aerodynamics, which is not discussed. i know that i only see consistent/measurable differences in speeds on segments which have pretty high averages, meaning some descending. the 28mm tires i’m on now come closer to the ideal profile with my current rims, and i definitely am braking more on descents that i do multiple times a week. wouldn’t be surprised if there was another 2mph at 35+. but it’s not really useful, since i’m braking it off, and at the more typical 15-20 average i see no difference at all other than a rougher ride.