Originally Posted by
biker128pedal
For best aero I think you want to match or come close to the rim outside rim width. A 23mm Conti GP5000 will measure about 26 to 27 mm wide on a 19 mm rim. A 25mm GP5000 will be slightly less than 28mm.
You are confusing GP4k and GP5k. GP4k was the tire that ballooned out to basically the next size up.