Correct Tire Size For New Wheels?

[Zoso]

Hey everyone, I just purchased a set of 2004 LS430 wheels for my 1st gen 1992 LS400 (17inch X 7.5 inch). I am trying to figure out what the correct tire size I need to match the wheel/tire combo diameter of my original 15inch wheels and standard tires for the 92 model? I would like to have the speedo stay as close to standard as possible. What tire size are you guys running on 17inch rims to keep the speedo in line? Any advice would be most helpful. Thanks!