This was intriguing me so I looked back through my about 100 mini magazines from a few years ago and the largest mini tyre I could find was a 175/50/13 and even that was pretyt rare most of them were no larger than 165. I did find one second hand ad selling 185/55/13s but dont know where they came from.

Looking at new tyres for my Honda atm as see on one of the pamphlets you can get a Dunlop Forumla 901 in 205/60/14. A wee bit bigger and probably wouldnt look right cause the side wall would be too big but its still an option