Originally Posted by
PeteHski
Some of the pressure calculators are based on your actual measured tyre width and some are based on nominal stated tyre width, along with internal rim width. But they are both approximations as they rarely cater for specific tyre models and I don’t know any calculators that include tyre height as a specific variable.
But in any case they are just a guide to setting tyre pressure and usually get you in the right ball park.
I guess so, but at the same time I'm thinking how different these 2 tires's sizes could be considered different if you think of the shape as more ovalized.
Nominally, you could quickly (incorrectly) think a 27mm inflated width tire is only 4% greater in size than a 26mm tire, but with an ovalized area and the height differential, it grows to perhaps about a 12% difference. Since the various tire pressure calculators don't include height, the ballparks can be quite large in size.