Well the smallest tyre you can have is a 195/40/16. This will not fit on the 8.5" rim.
Next is a 195/45/16- again no good
Next you have 205/40/16- would be well too stretched.
205/45/16 is a weird looking thing...don't bother
Smallest fit would be a 215/40/16 but it would need to be a quality tyre as a budget one would nt stretch and seal so goo.
Yokohama 215/40/16 A539 ideal at £60 inc VAT.