I am curious about the Conti GP 4 Season widths as well in size 700 x 28. I've got 25s in Conti GP 4000s and they are about 24 mm wide. I've also got some Michelin Pro2Race 25s and they measure 27-28 mm wide. However, the volume seems about the same on both tires because the Contis are taller. The Michelins measure a true 25 mm in height (from rim to outside diameter), and I suspect the Conti 25s measure about 26-27 in height. I know the Contis are taller because their diameter is larger when I measured it using the "roll out method" for calibrating my bike computer.