Originally Posted by
Hiro11
Totally normal: the dimensions printed on the sidewall are only directional as true measured width can vary widely based on the specific manufacturer and on the specific rim you're using.
wat
This is the same rim and same model tire, just a different size. That should eliminate any of the variation you associate to different tire brands and rim profiles.
As a consumer, I expect a 28mm tire to be about 3mm wider than a 25mm tire that is the exact same brand and model when mounted on the same rim.
That's a bare minimum expectation, really.