The 19s were 255/45-19?
To your point...stock size tires are 245/35-19 which has an overal diameter of 25.752. In your case, you will be running 255/45-18 which as an overal diameter of 27.035. That is quite a difference.
Non-winter tires, people run 255/35-19 which has a diameter of 26.028. Anything bigger it starts to depend on offsets of the wheels which might be your case as well.
I am not a tire person, just thinking out loud. I used this as my tire calculator for estimates:
http://www.csgnetwork.com/tiresizescalc.html