I'm posting this to C&V instead of Bike Mechanics because it is more a reflection of how things were a few decades ago.

Today I replaced some old tires. The one on the front was a Specialized, marked 1-1/8", 110psi. It was noticeably narrower than the Pasela TG 1-1/8" I had put on the slightly narrower rear wheel. Okay, so that just shows that tires can be different even with the same markings.

But then I noticed that embossed on the sidewall was 23-630. Huh? No, it was not a 28 smudged out to form 23. I looked again. It was definitely 23. So what is it supposed to be, I asked myself? Wider than an inch or narrower? When inflated the sidewalls measured about 27mm, what I would have expected.

Curious.

Panaracer sizes relatively truthfully; everyone else simply makes their casings smaller. A Pasela is almost always equal to the next size down in reference to the 27" tires:

27x1" = everyone else's 27x1-1/8"
27x1-1/8" = everyone else's 27x1-1/4"
27x1-1/4" = everyone else's 27x1-3/4"

-Kurt

Yeah, but... The curiosity was not the real size but the contradictory markings. The multi-colored label was correct, more or less. The number embossed in the sidewall wasn't even close. Given that Specialized was one of the first companies to come out with high-pressure narrow clinchers (as far as I remember it) I won't blame them for being aggressive with the specs. But you'd've thought they could be more consistent.

Are you measuring 27mm side to side, or bead to top?

Perhaps the 1-1/8" marking means that's the approximate inflated width on whatever rim they expect you to use. The ETRTO size (23-630) is measured a specific way. They didn't measure the actual inflated width. They measured the linear distance between the beads of the tire (when flattened out) and divided by 2.5.

That was measured outside sidewall to sidewall with a caliper. It is of course approximate. I wasn't trying to match marking to actual size. I measured it only because it was visibly smaller than the 1-1/8" Pasela on the rear, so I wanted to compare them to check my perception. I didn't notice the contradictory markings until days later.

Thanks! That's interesting. I have observed from a limiited set of tires that the 27x1-1/8 Vittoria Zafiros I have are very similar in size to my Pasela 27x1-1/8. And my Kenda Kriterium 700x25 are very similar in cross section to my Pasela 27x1.

For what it's worth, I have a pair of Michelin tires that are labeled both 27 x 1 and 27 x 1 1/8.

Oh, and I have one, I think it's a Continental, that's labeled both 700 x 28 and 27 x 1 1/8, but that's just an obvious ****-up (it's a 700c tire).

23-630 would be the ISO tire size, the inner width of the rim is 23mm and the bead seat diameter of the rim is 630mm. ISO tire sizes are based on the size of the rim the tire fits, not the physical size of the tire, which would be about right for a 27" x 1¼" inch tire. Newer tires should have both marked on them, which the tires you have probably are.

Sheldon Brown says more here