FWIW my 28c Paselas actually measure 26.5mm. That's on an M13II rim. An example of one is hardly enough to make a deduction from, but it might be guessed that Panaracer Paselas run a little small. Therefore, if you're not sure if you should go with 27x1 or 27 x 1 1/8", the 1 1/8" may be a better bet. Also, 1 1/8" tires will generally fit OK on both narrow and wide road rims. If you have wider touring rims, 1" tire fit is going to be less than ideal.