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've had one of these for a while now. It's well made and has held up to a lot of abuse
https://m.aliexpress.com/item/32236193792.html?spm=a2g0n.orderList.0.0.6988369bw3LTcF