I don't remember sorry.
I'm currently running a 2.2" bmx tyre on it, though it'd only work with (and is drilled for) presta valves. So thinking about it maybe not so wide. If I manage to get the bike into a workshop sometime soon I'll measure it and report back
I bought them because they have 25mm outer 18mm inner width. Do you recall what is the outer width of these kinlins?