Originally Posted by
SoSmellyAir
More recent 25c tires (e.g., Continental GP5000) are narrower than previous 25c tires (e.g., Continental GP4000 S II). 700x25c GP5000 tire measures < 23 mm wide when first mounted on my 17 mm (internal width) Mavic wheels, but after multiple rides and pre-ride inflations stretched to 25 mm.
I recently picked up a pair of Vittoria Corsa 700x30. Mounted on 17mm rims, they measure at, generously, about 26.5mm.
They're very nice and run smooth, and probably are designed to go with a wider internal x-section, but on my wheels they are skinnier than advertised.