Well I just measuered a fresh 25mm vittoria rally on a narrow rimmed ambrosio disc and it came out between 25.1 and 25.5mm from edge of rim to top of tyre at 130 PSI.
VS a 23c hardshell on a 23mm rim at 22.76 most of the way round at 75PSI.
Maybe this will give you some idea?
Might be ghosts in my head, but doesn't the diameter from rim edge to rim edge come out a couple of mm shorter on tubular rim, than on clincher rim.
@Thuekr started
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Well I just measuered a fresh 25mm vittoria rally on a narrow rimmed ambrosio disc and it came out between 25.1 and 25.5mm from edge of rim to top of tyre at 130 PSI.
VS a 23c hardshell on a 23mm rim at 22.76 most of the way round at 75PSI.
Maybe this will give you some idea?