Benim, bu konu ile ilgili bir ingiliz forum sitesinden elde ettiğim bilgiyi aşağıda ekledim, skoda2 nin yorumu gayet doğru gözüküyor, tavsiye etmem;
I use the standard fitted 225/50/17 tyres in the summer, and 215/60/16 in winter. The ride on the 16" wheels is far more comfortable than on the 17". To fit 18" wheels would reduce the cushioning even further than the 17". The Yeti has a stiff suspension, with the wheels you suggest you will feel every single bump in the road no matter how small. Unless you can test the wheel /tyre combination without spending any money (i.e. borrow them from a friend) don't do it. You could find it a very expensive mistake. If you want a car suited to such tyres don't buy a Yeti.
The circumference of the standard 17" tyre is 206.34 cm, the 18" would be 210.08 cm, so your speedo would under read by 1.8% so 30 mph would be 30.5 mph.
