Yeah, it's got a 16" rear and an 18" front.
From what I gather, the wheels went up an inch sometime after 1977.
I think the bigger wheels are on the TY50p.
I've got to say mind, I'm impressed with how quickly the replies have been coming...thanks for that
I've recently bought the bike which I intend to fully restore due to the fact that I've always loved them since first riding one 33 years ago when I was 14!!