actual "27" is very old standard you might see such as if you discover an unused road bike from the early 1980s deep in somebody's garage. It's quite rare these

actual "27" is very old standard you might see such as if you discover an unused road bike from the early 1980s deep in somebody's garage. It's quite rare these days. 27.5 is used for mountain bikes so the rim profile and tire widths are a completely different thing than old "27"