Originally Posted by
waxnomadic
Is it reasonable to assume that the height of a 28c tire would be 5mm more than a 23c, as well, or something less?
They often aren't quite what you would expect so the only real answer is to try, preferably at the LBS. I put 28c Randonneurs on my giant and found they were about the same size as GP4000 25s (better puncture protection though).