Originally Posted by msu2001la

Worth noting that Conti has 3 versions of this tire. Tubed, Tubeless (TL) and Tubeless/hookless compatible (S TR). I have used all three in various widths, and all measure differently.

Currently:
28mm GP5000 with tubes @80psi on a 23mm external carbon rim (I'm guessing 18-19mm internal but I've never measured) = 26.2mm actual

28mm GP5000 S TR w/o tubes @60psi on a 27mm external/23mm internal hookless carbon rim = 27.8mm actual

I have a set of 32mm TL's, not currently mounted, but I had these on a 19mm i.d. alloy rim last summer and recall them being slightly less than actual 32mm size.